Airphoto Mosaic Training Workbook

Airphoto Mosaic Training Workbook
ER Mapper 6
Level One
Training Workbook
for
Airphoto Mosaic Applications
19 November 1999
ER Mapper
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Summary Contents
About this workbook xiii
Part One - Airphoto Mosaic Applications 15
1 Airphoto mosaics and ER Mapper 17
2 User interface basics 29
3 Importing and viewing an image 49
4 Viewing an image in RGB 73
5 Image rectification 89
6 Image orthorectification 113
7 Assembling image mosaics 141
8 Color balancing images 157
9 Removing seam lines 177
10 Creating the final mosaic 195
11 Color balancing image mosaics 207
12 Composing maps 217
13 Compressing images 245
14 Exporting to GIS systems 253
ER Mapper Workbook - Airphoto Mosaic Applications v
Summary Contents
Part Two - Enterprise Wide Imagery 273
About this section 275
15 Enterprise Wide Imagery 277
16 Using ER Viewer 283
17 Office applications (OLE) 291
18 ArcView GIS Users 301
19 MapInfo Users 317
20 Autodesk World Users 335
A System setup 351
B Reference texts 353
Index 355
vi ER
Mapper Workbook - Airphoto Mosaic Applications
Table of Contents
About this workbook xiii
1 Airphoto mosaics and ER Mapper 17
Overview of airphotos and applications 17
Types of airphotos 18
Digitizing (scanning) of airphotos 19
Creating airphoto mosaics 20
Image processing concepts 25
Traditional image processing 26
ER Mapper image processing 27
2 User interface basics 29
User interface components 29
Hands-on exercises 35
1: Using menus and toolbars 35
2: Opening windows and algorithms 38
3: Resizing windows and zooming/panning 39
4: Managing multiple image windows 44
3 Importing and viewing an image 49
About the algorithms concept 49
Hands-on exercises 53
ER Mapper Workbook - Airphoto Mosaic Applications vii
Contents
1: Opening an airphoto image file 54
2: Displaying an image in greyscale 56
3: Selecting bands and adjusting contrast 59
4: Labelling and saving the algorithm 68
5: Reloading and viewing the algorithm 70
4 Viewing an image in RGB 73
About RGB color images 73
Hands-on exercises 74
1: Creating RGB algorithms 75
2: Working with algorithm layers 79
3: Loading, adding and changing layers 82
4: Labelling and saving the algorithm 87
5 Image rectification 89
About image rectification 89
Hands-on exercises 91
1: Setting up the raw and reference images 92
2: Picking the first four GCPs 95
3: Picking additional GCPs in the images 101
2: Perform the image rectification 106
3: Evaluating image registration 109
6 Image orthorectification 113
About orthorectification 113
Hands-on exercises 115
1: Orthorectify an airphoto using GCPs 115
2: Orthorectify an airphoto using Exterior Orientation 134
7 Assembling image mosaics 141
About assembling mosaics 141
Hands-on exercises 142
1: Creating a greyscale image mosaic 143
2: Creating mosaics automatically 149
2: Creating an RGB image mosaic 153
viii
ER Mapper Workbook - Airphoto Mosaic Applications
Contents
8 Color balancing images 157
About color balancing 157
Hands-on exercises 159
1: Using brightness shift formulas 160
2: Create a mosaic of balanced images 166
9 Removing seam lines 177
About regions and feathering 177
Hands-on exercises 180
1: Determining areas of overlap 181
2: Defining regions to constrain overlap 183
3: Feathering images within regions 189
10 Creating the final mosaic 195
About algorithms as templates 195
Hands-on exercises 196
1: Creating green and blue band mosaics 197
2: Creating the final RGB algorithm 201
11 Color balancing image mosaics 207
Hands-on exercises 207
1: Color balancing the mosaic 208
12 Composing maps 217
About map composition 217
Hands-on exercises 218
1: Setting up the page 219
2: Adding a clip mask around the image 224
3: Drawing vector annotation 227
4: Defining map objects 233
13 Compressing images 245
About ECW compression 245
Saving a compressed image to disk 246
14 Exporting to GIS systems 253
About use in GIS systems 253
Using compressed images in GIS systems 255
ER Mapper Workbook - Airphoto Mosaic Applications ix
Contents
Hands-on exercises 255
1: Defining an area of interest 256
2: Creating a UDF dataset 257
3: Creating a “.hdr” file for ESRI products 264
4: Saving a subset image to a TIFF file 266
About this section 275
Chapter contents 275
15 Enterprise Wide Imagery 277
Using imagery within your organization 277
Enterprise wide imagery 278
ER Mapper free imagery solutions 279
Using ER Mapper for imaging 279
ER Mapper image compression 280
Working with large images 281
16 Using ER Viewer 283
About ER Viewer 283
Hands-on exercises 284
1: Using ER Viewer to display images 284
17 Office applications (OLE) 291
What is OLE? 292
Sharing image files using OLE 292
Hands-on exercises 293
1: Using OLE to display images 294
18 ArcView GIS Users 301
About the ER Mapper Extension for ArcView GIS 301
Using the extension with ER Mapper 302
How to obtain the ER Mapper Imagery Extension 302
Hands-on exercises 303
1: Using the ER Mapper extension 303
19 MapInfo Users 317
About the MapImagery plug-in for MapInfo 317
How to obtain the free MapImagery plug-in 318
x
ER Mapper Workbook - Airphoto Mosaic Applications
Contents
Hands-on exercises 318
1: Open an ER Mapper image file 319
2: Open ER Mapper algorithm files 322
3: Overlay MapInfo vector data 327
4: MapImagery settings and options 330
Table (.tab) files created by MapImagery 330
Algorithm (.alg) files created by MapImagery 330
Choosing map projection information 331
The Supersampling setting 332
Contrast enhancement options 332
20 Autodesk World Users 335
About Autodesk World’s ER Mapper image viewing engine 335
Using Autodesk World with ER Mapper 336
Hands-on exercises 336
1: Inserting an ER Mapper image 337
2: Inserting multiple coregistered images 341
3: Combining image and drawing data 346
A System setup 351
Windows installation of training datasets 351
B Reference texts 353
Index 355
ER Mapper Workbook - Airphoto Mosaic Applications xi
Contents
xii
ER Mapper Workbook - Airphoto Mosaic Applications
About this
workbook
This workbook is intended to get you started learning and using ER Mapper to
create mosaics of digital aerial photographs. It provides simple step-by-step
lessons that give you hands-on practice using the basic features of the software,
and using more advanced features as well. Please read the following important
information before beginning.
•
Chapter contents
•
Setting up practice datasets
•
Typographical conventions used in this document
Note: The hands-on exercises in this workbook require that example airphoto datasets
have been installed. These are included with ER Mapper 6. Please refer to
Appendix A “System setup” in this manual for installation instructions.
This manual is not intended to cover all ER Mapper functionality, and does not
cover concepts of digital photogrammetry such as DEM generation. Please refer to
the ER Mapper Tutorial and User Guide manuals for more detailed information as
needed. (These are also accessable directly from the online help system.)
ER Mapper Workbook - Airphoto Mosaic Applications xiii
About this workbook
Chapter contents
The chapters in this manual give you extensive hands-on experience using the
ER Mapper software through a series of specially designed lessons. Most lessons
have two basic sections:
•
an overview of key concepts
•
a series of step-by-step hands-on exercises
It is recommended that you start at the beginning and proceed through the chapters
in order because the later chapters build on concepts learned in earlier ones.
The emphasis of this manual is on learning and using the ER Mapper software, not
on teaching image processing, airphoto interpretation, and other concepts. For
more detailed information on the concepts or specific applications, please refer to
Appendix B “Reference texts” in this manual.
Setting up practice datasets
The exercises in this manual assume that ER Mapper 6 is installed and licensed,
and that the example airphoto datasets have been installed in an
‘airphoto_training’ directory. For information on configuring your system for
these exercises, please refer to Appendix A “System setup” in this workbook.
Typographical conventions
The following typographical conventions are used throughout this document:
•
ER Mapper menus, button names and dialog box names are printed in boldface
Helvetica type, for example:
“Select Print from the File menu to open the Print dialog box.”
•
Where you are asked to click the mouse on an icon button in the user interface, both
the button and its formal name are indicated in the text. For example:
“Click on the Edit Transform limits
•
button.”
Text to be typed in a dialog box text field is shown in boldface Courier typeface, for
example:
“Type RGB_airphoto_mosaic in the text field.”
xiv
ER Mapper Workbook - Airphoto Mosaic Applications
Part One Airphoto
Mosaic
Applications
1
Airphoto mosaics
and ER Mapper
This chapter provides an overview of airphoto concepts and steps used for creating
mosaics of digital airphotos. It also describes the basics of image processing and
use of the ER Mapper software in assembling airphoto mosaics.
Overview of airphotos and applications
Aerial photography has been used for many years to create maps for a wide variety
of applications. The first known aerial photograph was taken from a balloon over
Biervre, France in 1858. Airphotos were used extensively for mapping during the
first and second world wars, and for intelligence gathering during the cold war era.
Aerial photographs are taken from an aircraft to capture a series of images using a
large roll of special photographic film. The film is then processed and cut into
negatives. The most common size for negatives is 9" x 9" (23cm x 23cm). The
final scale of the aerial photograph depends on the height of the aircraft when the
photo was taken. Aerial photographs are taken with an overlap between each one,
to ensure that a final mosaic can be assembled.
Airphotos are now being used extensively as basemaps for updating vector data
that is stored and manipulated in GIS and DMS systems. Often it is necessary to
create a mosaic of several airphotos to cover the desired area. Common uses and
mapping applications for airphotos include:
ER Mapper Workbook - Airphoto Mosaic Applications 17
Chapter 1#Airphoto mosaics and ER Mapper z Types of airphotos
•
land use/land cover mapping
•
urban and regional planning
•
environmental assessment
•
civil engineering
•
geologic and soil mapping
•
agricultural and forestry applications
•
water resource and wetland applications
Types of airphotos
There are generally four types of airphotos in common use, and these are created
by using specific types of film in the camera:
18
•
Panchromatic–often called black and white, is sensitive to the same range of light
wavelengths as perceived by the human eye (the “visible” wavelengths blue, green
and red spanning 0.4 to 0.7 micrometers). Panchromatic photos are most commonly
used for planimetric and/or topographic mapping. Digitized black and white photos
have a single band (layer of information), so they are usually displayed in greyscale
on a computer.
•
Natural color–often called true color, is also sensitive to the same wavelengths of
light as perceived by the human eye. Digitized natural color photos have three
separate bands, one each for the blue (0.4-0.5 micrometers), green (0.5-0.6) and red
(0.6-0.7) wavelengths of light. They are usually displayed using the RGB color
system on a computer to recreate the same colors as on the photo print. Natural
photos are commonly used for creating photo maps, or for mapping applications
that require discrimination of the color of features.
•
Infrared–often shortened to “IR,” is sensitive to a range of wavelengths that
includes the red, green and near infrared portions of the spectrum. The near infrared
wavelengths (0.7-1.0) cannot be perceived by the human eye, so they provide
information that beyond the human perception system. Like panchromatic,
digitized IR images have a single band and are usually displayed in greyscale.
•
Color infrared–often called false color or shortened to “CIR,” was developed
during World War II to aid camouflage detection. Digitized CIR images have three
separate bands, one each for the green (0.5-0.6), red (0.6-0.7) and near infrared (0.71.0) wavelengths of light. Like natural color, they are usually displayed using the
RGB color system to recreate the same colors as on the photo print. Vegetation
usually appears red on these images, thus the term false color. CIR photos are
commonly used for agricultural, forestry and wetland studies because the IR band
provides valuable information on vegetation health, species and biomass.
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 1#Airphoto mosaics and ER Mapper#z Digitizing (scanning) of airphotos
Digitizing (scanning) of airphotos
In order for an aerial photograph to be processed in a computer, the photo must
first be scanned or digitized to create a digital image file. The photo print or
transparency is run through a scanner, a device that converts visible images to
digital files. Many airphoto acquisition firms supply their photo data already
converted to digital image format, but you may also want or need to scan the
photos yourself.
Two factors affect the resolution, or size of features that can be detected, in the
digital image of the aerial photograph. These factors are:
•
The scale at which the aerial photograph was flown. This is based on aircraft
altitude above ground and focal length of the camera during photo acquisition.
•
The Dots Per Inch (DPI) used to scan the aerial photo. This determines the size on
the ground, in meters or feet, of one pixel on the digital aerial photograph, and
approximately corresponds to the size of the smallest feature that can be detected.
Use the following table to decide what scale aerial photography to use and what
DPI resolution to use when scanning the photos. A pixel size of 1 meter is
adequate for many applications.
ER Mapper Workbook - Airphoto Mosaic Applications 19
Chapter 1#Airphoto mosaics and ER Mapper z Creating airphoto mosaics
Photo scale:
10000
24000
40000
Km. across:
2.3
5.5
9.1
Scanned image file sizes:
Pixel size in meters:
# of pixels
color
B&W
150 dpi scan
1.7
4.1
6.8
1350
5 Mb
2 Mb
300 dpi scan
0.8
2.0
3.4
2700
21 Mb
7 Mb
600 dpi scan
0.4
1.0
1.7
5400
83 Mb
28 Mb
1200 dpi scan
0.2
0.5
0.8
10800
334 Mb
111 Mb
2400 dpi scan
0.1
0.3
0.4
21600
1335 Mb
445 Mb
Ask your aerial photograph supplier if they can provide you the aerial photographs
pre-scanned, on a CD-ROM, in ER Mapper or TIFF format. This will save you
having to scan the photos yourself.
Creating airphoto mosaics
An airphoto mosaic is an assemblage of two or more overlapping photographs that
form a composite view of the area covered by the individual photos. Typically the
aircraft flies back and forth across an area acquiring a set of photos that overlap,
then the photos are scanned, rectified and assembled into a mosaic.
Aircraft flight
while taking aerial
photographs
20
Photo
#1
Photo
#2
Photo
#6
Photo
#5
ER Mapper Workbook - Airphoto Mosaic Applications
Photo
#4
Chapter 1#Airphoto mosaics and ER Mapper#z Creating airphoto mosaics
The basic steps involved in creating a mosaic of airphotos are shown below. These
steps are covered in detail in the exercises in this workbook.
Digitize
airphotos
Scan (digitize) airphoto hardcopy prints or transparencies
to create digital image files, or acquire digital format
photos saved in image formats such as TIFF.
Import
digital
airphotos
Read digital airphoto image files stored on tape,
CD-ROM, etc. and convert to ER Mapper image
format (using ER Mapper import utilities)
Initial
image display
& evaluation
View image data on a CRT monitor to evaluate
quality or areal coverage, or display statistical
information such as histograms or cell values.
Image
rectification
Geometrically correct (rectify or geocode) images to
correspond to geodetic coordinate systems and map
projections such as UTM, State Plane, etc.
Image
enhancement
& correction
Create
mosaic
of images
Annotation
& map
composition
Data export
& hardcopy
printing
Digitally process individual images to aid visual
interpretation, highlight specific features, or correct
color/brightness shifts and imbalances.
Assemble rectified, enhanced images into a mosaic,
balance contrast across the mosaic, and apply techniques
to minimize visible seam lines between adjacent images.
Setup map size/scale, and annotate mosaic of images
with text, lines, shaded polygons, legends, scale
bars, coordinate grids and other map objects.
Export all or part of processed mosaic to GIS and DMS
software, or print subsetted images or annotated
raster/vector maps to hardcopy devices or files.
ER Mapper Workbook - Airphoto Mosaic Applications 21
Chapter 1#Airphoto mosaics and ER Mapper z Creating airphoto mosaics
Data import
The first step in creating an airphoto mosaic is importing the data you want to use
into ER Mapper. Typically the data might be stored on magnetic tape, CD-ROM,
or other media. There are two primary types of data you may want to import into
ER Mapper: raster and vector.
Raster image data is the type used as input to image processing operations, for
example a digitized aerial photograph. When you import a raster image file (using
ER Mapper’s import utility programs), ER Mapper converts the data and creates
two files:
•
a binary data file containing the image data, in band interleaved by line (BIL)
format
•
a corresponding ASCII header file with an “.ers” file extension
Vector data is stored as lines, points, and polygons. Many geographic information
system (GIS) products use vector data structures because it is more efficient for
representing discrete spatial objects like roads (lines), sample locations (points), or
political boundaries (polygons). In an image processing product, it is often helpful
to use vector data as a source of ground control for rectifying raw airphotos, or
overlaying vector data on top of a raster image backdrop. When you import a
vector file (using ER Mapper’s import utility programs), ER Mapper converts the
data and creates two files:
•
an ASCII data file containing the vector data
•
a corresponding ASCII header file with an “.erv” file extension
Note: You can open image files in many different formats in ER Mapper without having
to import them as ER Mapper raster datasets.
Image display
After importing the data, the next step is usually to display the image on your CRT
monitor to evaluate the data quality, geographic area of coverage, and coverage of
overlapping areas with other images used in a mosaic. If the data is of poor quality,
you might decide to digitize the photos again. If it has significant cloud cover or
haze over your area of interest, you might try to obtain better data.
There are two primary ways airphotos are viewed:
22
•
black and white, or greyscale, displays (used to view black and white airphotos or
a single band of a color airphoto)
•
red-green-blue (RGB) color composite displays (used to view all three bands of a
color or color IR airphoto to reproduce the look of the original print)
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 1#Airphoto mosaics and ER Mapper#z Creating airphoto mosaics
The way in which you choose to display your raster data is called the “Color
Mode” in ER Mapper. You can also view data in traditional two-dimensional
planimetric views, or 3-D perspective views if you have an elevation dataset such
as a DTM.
In addition to displaying the data, you may want to view statistical information
about it. Statistics are often good indicators of image quality. You may want to
calculate statistics for the image, such as the mean value in each band, and view
them in a tabular format. Or you may want to view statistical information in a
graphical format using tools like histograms, scattergrams, and traverse profiles.
Image geocoding
Many times, raster image data is supplied in a “raw” state and contains geometric
errors. Whenever accurate area, direction, and distance measurements are required,
raw image data must usually be processed to remove geometric errors and/or
rectify the image to a real world coordinate system.
•
Registration is the process of geometrically aligning two or more images to allow
them to be superimposed or overlaid.
•
Rectification is the process of geometrically correcting raster images so they
correspond to real world map projections and coordinate systems (such as Latitude/
Longitude or Eastings/Northings).
•
Orthorectification is a more accurate form of rectification mainly used on
airphotos. It takes into account properties of the camera used to take the images, and
fiducial marks on the image.
If your application requires that your images be registered to one another or
rectified to a map projection, you will use ER Mapper’s Geocoding Wizard to do
this.
Image enhancement and correction
Image enhancement refers to any one of many types of image processing
operations used to digitally process image data to aid visual interpretation, extract
quantitative information, or correct color/brightness distortions. Image
enhancement is what many people commonly think of as “image processing.”
In ER Mapper, image enhancement operations are greatly simplified by the
“algorithms” processing concept. Nearly all types of image enhancement
operations can be applied and displayed in real time to provide truly interactive
control without writing temporary files to disk.
Typical image enhancement operations include:
ER Mapper Workbook - Airphoto Mosaic Applications 23
Chapter 1#Airphoto mosaics and ER Mapper z Creating airphoto mosaics
•
Contrast enhancements–Improve image presentation by maximizing the contrast
between light and dark portions (or high and low data values) in an image. Or,
highlight a specific data range or spatial area in an image.
•
Formula processing–Apply mathematical operations to derive specific thematic
information or correct/normalize color and brightness shifts across an image. An
example would be the color balancing formulas to correct color shifts supplied with
ER Mapper.
•
Filtering–Enhance edges, smooth noise, or highlight or suppress specific linear or
spatial features in images. For example, apply edge enhancement filters to enhance
detail (sharpen) the image or smoothing filters to reduce noise.
•
Image merging (data fusion)–Combine images with different qualities to aid
interpretation. For example, merge a black and white airphoto with a multispectral
satellite image to combine satellite spectral information with airphoto spatial detail.
•
3-D perspective visualization–Create realistic 3-D perspective views simply by
adding a “height” element to the airphoto image display, such as digital terrain/
elevation data or any other type of data that may aid visualization and interpretation.
•
Color balancing–Use the ER Mapper Color Balancing Wizard to balance
mosaiced images to produce a seamless single image.
Creating image mosaics
A mosaic is an assemblage of two or more overlapping images used to create a
continuous representation of the area covered by the images. ER Mapper
automates the building of image mosaics because co-registered images referenced
in the same processing algorithm are automatically displayed in their correct
geographic positions relative to each other.
This means that you can work with each image file in the mosaic as a separate
entity, and you are not required to write all images to one large file on disk in order
to process and enhance them. This capability is especially important when working
with large image files such as scanned airphotos, because final mosaics can
consume gigabytes of disk space if they would have to be saved in a single file.
The ER Mapper Image Display and Mosaic Wizard automatically mosiacs
images in a specified directory path.
Map composition
You can use ER Mapper’s built-in Annotation and Map Composition tools to
create top quality maps combining airphoto images or mosaics, vector, and tabular
data. Annotation lets you draw directly on-screen using text, line, polygon, and
other annotation tools, and specify fill color, shading, line styles, user-defined
symbols, and group, move and resize objects. Vector annotation files created in
ER Mapper can also be exported to external file formats for use in other products.
24
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 1#Airphoto mosaics and ER Mapper#z Image processing concepts
ER Mapper’s Map Composition tools let you create top quality image maps by
adding coordinate grids, map collars, scale bars, legends, north arrows, and many
other map objects and standard cartographic symbols. You can layout and compose
maps comprised of multiple processed images, and size and scale map output as
desired. All map objects are defined as full color PostScript, and you can easily
add custom map objects such as company logos or special north arrows.
Data export and hardcopy
Once you have completed processing your data, ER Mapper lets you translate
raster and vector data to external standard file formats or print to over 200 different
hardcopy devices. You can easily print both 2-D planimetric and 3-D perspective
views.
•
ECW Compression enables you to save your imagery in compressed format for use
in other applications.
•
Data export is used to export all or part of a processed airphoto mosaic for use in
other software products, such as a backdrop for a GIS or DMS (desktop mapping
system) product. Or, you may want export vector annotation or vectorized thematic
data to a GIS product.
•
Free plug-ins enable you to open ER Mapper images, including ECW compressed
images, from within many GIS products.
•
Hardcopy printing is often the final goal of processing and annotating images, and
ER Mapper provides unsurpassed hardcopy support and output to standard graphics
file formats. ER Mapper also includes a built-in PostScript-compatible rendering
engine, so you get PostScript-quality output (such as beautiful, smooth text) on any
supported device, whether the device supports PostScript or not.
You can also easily print at exact sizes and map scales, and automatically print
large images in strips for assembling a mosaic of prints. Supported hardcopy
devices include inkjet printers, laser printers, dye sublimation printers,
electrostatic plotters, and film recorders. Graphics file formats include PostScript,
TIFF, Targa, CGM, and CMYK and RGB color separations.
Image processing concepts
The term digital image processing refers to the use of a computer to manipulate
image data stored in a digital format. The goal of image processing for earth
science applications is to enhance geographic data to make it more meaningful to
the user, extract quantitative information, and solve problems.
A digital image is stored as a two-dimensional array (or grid) of small areas called
pixels (picture elements), and each pixel corresponds spatially to an area on the
earth’s surface. This array or grid structure is also called a raster, so image data is
ER Mapper Workbook - Airphoto Mosaic Applications 25
Chapter 1#Airphoto mosaics and ER Mapper z Traditional image processing
often referred to as raster data. The raster data is arranged in horizontal rows
called lines, and vertical columns called samples. Each pixel in the image raster is
represented by a digital number (or DN).
columns
(samples)
rows
(lines)
110 81 57
87 61 42
69 44 31
raster image displayed as grey levels
(lower values displayed as dark greys)
enlarged view showing individual cells
or pixels and their corresponding DNs
For digitized airphotos, the DNs represent the intensity of reflected light in the
visible, infrared, or other wavelengths of the electro-magnetic spectrum. By
applying mathematical transformations to the digital numbers, ER Mapper can
enhance image data to highlight and extract very subtle information that would be
impossible using traditional manual interpretation techniques.
Black and white airphotos capture reflectance of ground features in a single range
of wavelengths, for example visible red/green or infrared (IR). Color airphotos
have three bands (or layers) of data covering the same geographic area, each
capturing reflectance of a different wavelength of light. A natural color airphoto,
for example, has three bands of data that record reflectance from the earth’s
surface in the red, green and blue wavelengths of light respectively.
Traditional image processing
Image processing was first developed on large mainframe computers in the 1960’s
to process images from planetary satellites. To process an image, you specified the
name of the file to process, the type of operation you wanted to perform, then
26
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 1#Airphoto mosaics and ER Mapper#z ER Mapper image processing
waited for the system to process the data and write the results to a new image file
on disk (shown in the diagram below). You then used a separate display program to
view the output file and evaluate your results.
Input file
Single image
processing operation
Output file
With traditional systems, the changes resulting from the image processing
operation are saved in a separate output raster file.
With the introduction of powerful workstations in the 1980’s, processing of large
images could now be performed on the desktop. Surprisingly, nearly all image
processing products on the market today are still designed around this
“disk-to-disk” approach from the 1960’s. This means that to perform a processing
operation that requires several steps, you need to write an intermediate file to disk
for each step. Only when the final file is created can you view your desired results.
Since digitized airphotos typically have large file sizes (up to hundreds of
megabytes), this approach can consume tremendous amounts of time and disk
space, and if the result is not what you intended, you must often start all over
again.
ER Mapper image processing
Recognizing the restrictions inherent in traditional image processing software, the
creators of ER Mapper developed an entirely new approach. Instead of writing a
file to disk for each processing step, ER Mapper lets you combine many
processing operations into a single step, and render the results directly to your
screen display in near real-time. (In most cases, no processed copies of your
original data are written to disk unless you request to do so.) The set of processing
steps you apply to your data is called an “algorithm” in ER Mapper.
Input file
Processing algorithm:
- formulas (corrections, etc.)
- filters (sharpen, edges,)
- contrast & brightness
- seam feathering, etc...
Image
display
With ER Mapper, you save only a description of the processing steps you wish to
apply to the data (the algorithm), not separate processed copies of the original
raster data file. By storing the processing steps separately from the actual data,
image processing becomes faster, easier to learn, and more interactive.
ER Mapper Workbook - Airphoto Mosaic Applications 27
Chapter 1#Airphoto mosaics and ER Mapper z ER Mapper image processing
In ER Mapper, algorithms can be used for simple viewing of data such as
greyscale or RGB band combinations. Algorithms are also used for complex
processing and modelling operations involving many images, transformations of
the data, and overlays of vector data–in both 2-D planimetric and 3-D perspective
views.
The algorithms design also allows ER Mapper to easily handle very large airphoto
images (and mosaics of images) much more efficiently than traditional systems.
Reducing the need to write processed copies of the data to disk is a very important
consideration.
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2
User interface
basics
This chapter introduces the basic use of the ER Mapper graphical user interface. It
gives you practice using menus, toolbars, dialog boxes, and image windows, and
loading and displaying image processing algorithms.
Note: In order to complete the exercises in this manual, you will need to access the
example images and algorithms supplied with ER Mapper. If needed, ask your
system manager for the location of the ER Mapper software directory at your site.
User interface components
This section provides a brief introduction to the main components of ER Mapper’s
graphical user interface (GUI). You can perform nearly all operations by pointing
and clicking with the mouse, and very little typing on the keyboard is required. The
GUI is part of ER Mapper’s original design, so it is well integrated and easy to
learn and use.
ER Mapper Workbook - Airphoto Mosaic Applications 29
Chapter 2#User interface basics#z User interface components
Using mouse buttons
When using ER Mapper, use the left button on your mouse to perform operations
like selecting items from menus, manipulating image windows, and drawing
annotation. In this manual, all actions are performed with the left mouse button
unless otherwise indicated. The following table explains terms used in this manual
to describe actions you perform with the mouse.
Term
Meaning
Point
Position the mouse pointer on an item.
Click
Point to an item, then quickly push and release the left mouse
button.
Right-click
Point to an item, then quickly push and release the right
mouse button.
Double-click
Point to an item, then quickly click the left mouse button
twice.
Drag
Point to an item. Then press and hold down the left mouse
button as you move the pointer to a new location, then release
the button.
Shift-click or
Ctrl-click
Hold down the Shift key or Ctrl key on your keyboard, then
click.
Shift-drag or
Ctrl-drag
Hold down the Shift key or Ctrl key on your keyboard, then
drag the mouse.
The symbol representing the mouse pointer on the screen changes shape
depending on what you are pointing to and the task you are performing.
Pointer
30
Location on the screen
Function
Menu bars and buttons; or
inside image window
Choose menu commands and click
buttons; point to the image to see
data values or coordinates.
Text fields
Type or select text, or reposition the
insertion point.
Inside the current image
window
Zoom the image within the image
window.
Inside the current image
window
Drag a box over an area to fill image
window.
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Chapter 2#User interface basics#z User interface components
Inside the current image
window
Pan the image within the image
window.
Inside inactive image
windows
Select an inactive window to become
the current window.
In image windows when
annotation tools are selected
Draw annotation and map
composition objects.
The ER Mapper main menu
When you start ER Mapper, the main menu appears. The main menu has two
primary components–the menu bar and rows of toolbar buttons.
Title bar
Menu bar
Buttons
Toolbars
Menu bar
Lets you select commands used to carry out actions in
ER Mapper. To select a command from the menu bar,
click on the name of the menu to open it, then click the
desired command name.
Toolbar buttons
Shows groups of buttons to let you carry out common
tasks quickly. To choose a function from a toolbar, click
on the desired button.
Tool tips
Place the cursor on any toolbar button and within a
couple of seconds the function of that toolbar button is
displayed in a small text window just below the cursor
Using ER Mapper toolbars
Toolbars give you quick access to many common functions, such as saving an
image processing algorithm or printing a hardcopy. ER Mapper also provides
optional toolbars for specific tasks and image processing applications. To hide or
display various toolbars, use the Toolbar menu. To get short help for any toolbar
function, point to the button and read the tool tips.
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Chapter 2#User interface basics#z User interface components
ER Mapper provides toolbars for many common tasks, and also toolbars for
building processing algorithms commonly used in remote sensing applications
such as forestry, geophysics, and map generation. The functions of the Standard,
and Common Functions toolbars are summarized below.
Standard
Provides quick access to standard commands for
opening and saving algorithms, printing, starting and
stopping algorithm processing, and changing the mouse
pointer. Most functions are also available from the
menu bar.
Common Functions
Provides quick access to commonly used functions,
such as creating general types of algorithms, viewing
and editing components of an algorithm.
Using ER Mapper’s scripting language, you can also create your own customized
toolbars for specific tasks and functions. For more information on creating custom
toolbars, see the ER Mapper User Guide.
Using dialog boxes
When you select menu commands or click toolbar buttons, dialog boxes often
appear for you to choose options to control your image processing tasks. Some
dialog boxes, such as the File Chooser, can disappear when you make your
selection. Other dialogs can remain open for setting options for as long as you
want to use them.
click to load
file
close dialog
without action
text fields
(click to
place cursor)
display setup
options
drop-down
list (click to
open)
access on-line
help for this
function
To resize a dialog box, drag one of its corners or edges to the desired size.
ER Mapper automatically resizes the dialog box intelligently, so that any central
display areas are enlarged, and the layout of buttons remains the same. After
resizing, the dialog retains your new size for the current ER Mapper session.
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Chapter 2#User interface basics#z User interface components
Using the File Chooser dialog boxes
When you choose to open or save a dataset, algorithm, or other file, ER Mapper
displays a File Chooser dialog box. The central window contains a list of
directories, or files in the current directory.
menu bar to
navigate and
mark directories
current directory
click to move up
and down one
directory level
scroll to view
other items
in directory
file types
click to load and
close dialog box
click to view
comments
click to load and leave dialog open
To open a file or directory displayed in the scroll list window, either double-click
on it, or click once to select it and click the OK or Apply button to open it.
Tip:
You can see more levels of directories and/or files by widening the file chooser
dialog box (drag one of the sides).
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Chapter 2#User interface basics#z User interface components
The File Chooser menus at the top have the following functions:
History menu
Use to change the File Chooser’s current directory.
The menu has two parts: the upper portion lists
most recently visited directories, and the lower
portion lists marked directories.
Special menu
Use to change to your home directory, or to mark or
unmark a directory (any directory may be marked
for fast access using the History menu).
View menu
Use to sort the contents of the current directory by
name, date modified, or date created.
Volumes menu
(Windows version only)
Use to access volumes or disk drives on your
network.
Directories menu
Use to change to any directory defined by your
preferences settings.
ECW URL History
List of the most recent ECW Compressed image
files accessed via an Image Web Server by means of
their URLs.
Using the on-line help system
ER Mapper provides an extensive on-line help system with both simple overviews
and detailed descriptions of all features and functions. There are two ways to
access help:
Help menu
Lets you browse all the standard ER Mapper
manuals on-line, and go between manuals and
topics using hypertext links.
Help buttons
The Help button inside dialog boxes gives you
context-sensitive help. If needed, you can navigate
to view more detailed information using the
hypertext links.
Typing text in text fields
To enter text for naming files or changing values in dialog boxes, ER Mapper
provides text fields. When you point to a text field, the pointer shape changes to an
I-beam. To enter text, click anywhere inside the text field to place the text cursor.
To select existing text, you can drag through the desired portion, or double-click on
a word or numeric value to select it. Text that is selected become reverse
highlighted, and any subsequent typing replaces it.
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Chapter 2#User interface basics#z Hands-on exercises
Hands-on exercises
The following hands-on exercises introduce you to the basic concepts of using
menus and dialog boxes and managing image windows.
What you will
learn...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Choose options from menus and toolbar buttons
•
Display and hide toolbars
•
Open an empty image window
•
Open an image processing algorithm into a window
•
Move and resize an image window
•
Zoom and pan the image within the window
•
Manipulate multiple image windows on the screen
•
Close image windows
1: Using menus and toolbars
Objectives
Learn to open and make selections from menus, use toolbars, and access on-line
help.
Move the ER Mapper main menu around the screen
1 Position the mouse pointer on the ER Mapper main menu title bar, then
drag it to the lower-left part of the screen.
Pointing to the title bar and dragging is how you move dialog boxes and image
windows around the screen.
2 Drag the main menu to the upper-right corner of the screen.
This is the recommended position for the main menu for the exercises in this
tutorial.
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Chapter 2#User interface basics#z 1: Using menus and toolbars
Open a menu to display its commands, then close the menu
1 Click on the View menu button; a list of commands under the menu
displays.
The small arrows next to Quick Zoom and Statistics indicate that they have
additional commands under them.
2 Click on the Statistics command to display its submenu.
3 Click anywhere outside the main menu to close the open menus without
making a selection.
Note: In the rest of this manual, selecting commands from menus is indicated as follows:
“From the Edit menu, select Preferences...” (which means click on Edit in the
menu bar, then click on the Preferences command).
Select the Print command from the menu bar
1 From the File menu, select Print.
The Print dialog box appears with options for printing hardcopy.
2 Click the Cancel button to close the dialog box.
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Chapter 2#User interface basics#z 1: Using menus and toolbars
Select the Print command from the Standard toolbar
1 On the Standard toolbar, click the Print
button.
Click to open
Print dialog
The same Print dialog box appears again. Using toolbar buttons is often a faster
way to access many commands in ER Mapper.
2 Click the Cancel button to close the dialog box.
Tip:
Many common commands on the menu bar, such as Print, are also available on the
Standard toolbar. Use whichever is fastest or most comfortable.
Display and hide a toolbar
1 From the Toolbar menu, select Forestry.
A third row of toolbar buttons appears on the main menu below the Standard and
Common Functions toolbars. This toolbar has buttons for common image
processing techniques used in forestry applications.
Forestry
toolbar buttons
2 Point the cursor to any button on the toolbar.
A description of the button function displays in the small text field just below the
cursor.
3 From the Toolbar menu, select Forestry again.
The Forestry toolbar buttons disappear from the main menu. Use the Toolbar
menu to display or hide any toolbar. (It is recommended that you always display
the Standard and Common Functions toolbars.)
ER Mapper Workbook - Airphoto Mosaic Applications 37
Chapter 2#User interface basics#z 2: Opening windows and algorithms
2: Opening windows and algorithms
To display an image in ER Mapper, you first open an empty image window, then
load and display an image processing algorithm. The algorithm references a raster
data file on disk, and the processing steps ER Mapper uses to enhance and render
the data on the screen display. (You will learn more about algorithms later.) You
can have as many different image windows open on the screen as you need.
Objectives
Learn to open image windows on your computer display, and open and run an
image processing algorithm stored on disk.
Open a new empty image window
1 From the File menu, select New.
An empty image window opens in the upper left corner of the screen. The window
title bar reads “Algorithm Not Yet Saved” because no processing algorithm is
associated with this image window yet.
Open and display an image processing algorithm
1 From the File menu, select Open....
The Open file chooser dialog box opens.
2 From the Directories menu, select the path ending with the text \examples
(The portion of the path name preceding it is specific to your site.)
3 Double-click on the directory named ‘Data_Types’ to open it.
4 Double-click on the directory named ‘Landsat_TM’ to open it. (Scroll if
needed to view it first.)
The list of example algorithms for processing Landsat Thematic Mapper (TM)
satellite imagery displays.
5 Double-click on the algorithm named ‘RGB_321.alg.’ (Scroll down if needed
to view it first.)
ER Mapper runs the algorithm and displays an enhanced Landsat TM image of
San Diego, California in the image window. This algorithm displays bands 3, 2,
and 1 of the Landsat image as an RGB color composite image, with band 3 in the
red display channel, band 2 in the green, and band 1 in the blue. Notice also that
the algorithm filename ‘RGB_321’ now appears in the title bar of the image
window.
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Chapter 2#User interface basics#z 3: Resizing windows and zooming/panning
Use the toolbar to open a different processing algorithm
1 Click the Open
button on the Standard toolbar.
The Open file chooser dialog box appears. (This toolbar button has the same
function as selecting Open... from the File menu.)
The algorithm named ‘RGB_321’ in the ‘Data_Types\Landsat_TM’ directory is
already highlighted since it is currently loaded into the image window.
2 Double-click on the algorithm named ‘RGB_541.alg.’
ER Mapper runs the algorithm and displays a color composite of the same Landsat
image, this time using bands 5, 4, and 1. Notice that the title bar also changes to
show the filename of the new algorithm.
Note: By default, ER Mapper runs the algorithm automatically for you when you open it
from disk. You can also reprocess the data at any time by clicking the Refresh
button.
3: Resizing windows and zooming/panning
Objectives
Learn to move and resize image windows, zoom (magnify) part of an image, and
pan (scroll) to other parts of an image.
Move the image window on the screen
1 Point the mouse at the image window title bar, then drag it to another part
of the screen.
2 Drag the image back to the upper-left part of the screen.
Like dialog boxes, dragging images by the title bar is how you move them around
the screen.
Resize the image window
1 Move the mouse pointer directly over the lower-right corner of the image
window–the pointer shape changes to a double ended arrow.
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Chapter 2#User interface basics#z 3: Resizing windows and zooming/panning
2 Drag the lower-right corner to make the window about twice its original
size, then release.
Image
window
Dragging any side or corner of an image window lets you change the default
window size as you desire.
Note: When you resize a window, ER Mapper maintains the size of the image inside the
window. Empty areas on the sides are filled with a cross-hatch pattern to indicate
that no data is displayed there.
Set the mouse pointer to Zoom mode
1 On the Common Functions toolbar, click the Zoom Tool
button.
This tells ER Mapper to use the mouse pointer for zooming when it is positioned
inside an image window. Also notice that the Zoom Tool button becomes
depressed to indicate that it is the active pointer mode.
2 Move the pointer inside the image window.
The mouse pointer displays as a magnifying glass icon.
Zoom in and out of the image with the mouse
1 Position the pointer in the center of the image, and click the left mouse
button.
The image zooms in by 50%.
2 Position the pointer in the center of the image, hold down the Ctrl. key while
clicking the left mouse button.
The image zooms out by 50%.
3 Position the pointer in the image, and then drag it up and down.
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As you drag the pointer down the image is magnified, i.e you zoom into it. When
you drag the pointer upwards, the image gets smaller, i.e you zoom out.
Set the mouse pointer to ZoomBox mode
1 On the Common Functions toolbar, click the ZoomBox Tool
button.
This tells ER Mapper to use the mouse pointer for creating a zoom box when it is
positioned inside an image window. Also notice that the ZoomBox Tool button
becomes depressed to indicate that it is the active pointer mode.
2 Move the pointer inside the image window.
The mouse pointer displays as a magnifying glass and box icon.
Zoom in (magnify) an area of the image with the mouse
1 Position the pointer near the upper-left center of the image, then drag to the
lower-right to define a box.
When you release the mouse, ER Mapper runs the algorithm again and magnifies
(or “zooms in”) on the area of the image you defined with the box. Dragging a
zoom box is a fast way to magnify an area of interest. (There are other zooming
functions you will learn about later.
Set the mouse pointer to Hand mode
1 On the Common Functions toolbar, click the Hand Tool
button.
This tells ER Mapper to use the mouse pointer for panning when it is positioned
inside an image window. Also notice that the Hand Tool button becomes
depressed to indicate that it is the active pointer mode.
2 Move the pointer inside the image window.
The mouse pointer displays as a hand icon.
Pan (scroll) the image within the window with the mouse
1 Click on the image. and drag it to a new position in the image window.
The hand pointer will grab the image and move it (pan) to the new location.
Zoom back out to view the full image extents
1 From the View menu, select Quick Zoom and then select Zoom to All
Datasets.
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Chapter 2#User interface basics#z 3: Resizing windows and zooming/panning
ER Mapper runs the algorithm again and zooms back out to display the full extents
of the Landsat image data. The Quick Zoom submenu provides many options for
zooming in or out to specific datasets, setting window geolinking, and other
options you will learn more about later.
2 Right-click inside the image window to open the shortcut menu, then select
Quick Zoom and then Zoom to All Datasets.
Right-click inside image
window to open
shortcut menu
Zoom and pan using buttons for predefined options
In addition to using the mouse, ER Mapper also lets you zoom and pan using
buttons to invoke predefined zoom and pan functions.
1 From the View menu, select Geoposition....
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Chapter 2#User interface basics#z 3: Resizing windows and zooming/panning
The Algorithm Geoposition Extents dialog box appears.
2 Click on the Zoom tab at the top to display zoom and pan options.
The Zoom tab options show sets of buttons for zooming and panning the image
within the window.
3 In the buttons labelled ‘Zoom,’ click the Zoom out 50%
button.
Click to zoom out 50%
ER Mapper runs the algorithm and zooms out to 50% of the previous display
resolution.
Tip:
For all icons on buttons under ‘Zoom’ and ‘Pan,’ the black square represents the
current image, and the white box represents how the size or position of the image
will change after the button is clicked.
4 In the buttons labelled ‘Set Extents To,’ click Previous.
ER Mapper zooms out to the previous image display extents.
ER Mapper Workbook - Airphoto Mosaic Applications 43
Chapter 2#User interface basics#z 4: Managing multiple image windows
5 Under ‘Zoom,’ click on the Zoom in 100%
button.
Click to zoom in 100%
ER Mapper magnifies the images to two times (100%) of the previous display
resolution (and keeps the image center point constant).
6 Under ‘Pan,’ click on the Pan left
button.
ER Mapper pans or scrolls the image 50% to the left (the previous center point is
now on the far right side of the image).
7 Under ‘Pan,’ click on the Pan upper-right
button.
ER Mapper pans the image 50% to the upper-right (the previous center point is
now on the lower-left corner of the image).
8 Experiment with other buttons under Zoom and Pan to see their effect.
9 Under ‘Set Extents To,’ click the All Datasets button.
ER Mapper resets the image extents to fit the entire dataset in the image window.
10 Click Close on the Algorithm Geoposition Extents dialog to close it.
4: Managing multiple image windows
Objectives
Learn to open a second image window, specify overlap priority between
windows, activate an image window, and close image windows.
Open a second image window
1 From the File menu, select New.
ER Mapper opens a new image window. As with all new image windows, it has no
algorithm associated with it yet.
Open and display a processing algorithm in the new window
1 From the File menu, select Open....
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Chapter 2#User interface basics#z 4: Managing multiple image windows
The Open file chooser dialog box appears.
2 From the Directories menu, select the path ending with the text
\examples.
3 Double-click on the directory named ‘Data_Types’ to open it.
4 Double-click on the directory named ‘SPOT_Panchromatic’ to open it.
The list of example algorithms for processing SPOT Panchromatic satellite
imagery displays.
5 Double-click on the algorithm named ‘Greyscale.alg.’
ER Mapper runs the algorithm and displays a SPOT Panchromatic satellite image
the San Diego (the same geographic area covered by the Landsat image in the other
window). The SPOT Pan data provides greater spatial detail than the Landsat data,
but has only one spectral band which is displayed in greyscale.
Move the SPOT window to overlap with the Landsat window
1 Drag the image window titled ‘Greyscale’ to the center of the screen until it
partially overlaps with the Landsat ‘RGB_541’ image window.
Your windows should be similar to the following diagram:
Landsat TM
window
SPOT Pan
window
Move one window in front of the other
1 Click on the title bar of the window with the algorithm description titled
‘RGB_541.’
The Landsat window moves in front of the SPOT window where there is overlap.
2 Click on the title bar of the window with the algorithm description
‘Greyscale.’
The SPOT window now moves in front of the Landsat window where there is
overlap. Clicking on the title bar of a window or dialog box bar lets you choose
which window or dialog box to display on top of others.
ER Mapper Workbook - Airphoto Mosaic Applications 45
Chapter 2#User interface basics#z 4: Managing multiple image windows
Select a window to be the active window
The “active” image window is the one you want to currently work with, such as
zooming, loading a new processing algorithm, or editing the current algorithm.
(You can have many image windows open on the screen, but only one can be
active.)
1 Look at the title bar of the SPOT Panchromatic window and notice the three
asterisks (***) on either side of the window title.
The three asterisks indicate that this is the active (or current) window of the two.
2 Move the pointer inside the image area of the window with the algorithm
description titled “RGB_541.”
The pointer shape changes to a pointing hand. (This happens whenever you move
from the active window to any inactive image window.)
3 Click anywhere inside the Landsat image window or on the Title Bar.
It now becomes the active window and three asterisks appear next to the title.
4 Click inside the SPOT window or on the Title Bar again to make it active.
Note: A window can be active and still be covered by another “inactive” window. To
move the active window to the front, click on its title bar.
Close both image windows
1 Close one image window using the window system controls:
•
For Windows, select Close from the window control-menu.
The window closes and disappears from the screen.
2 Close the other image window by repeating Step 1.
The window closes and disappears from the screen. Only the ER Mapper main
menu is now open.
What you
learned
46
After completing these exercises, you know how to perform the following tasks in
ER Mapper:
•
Choose options from menus and toolbar buttons
•
Display and hide toolbars
•
Open an empty image window
•
Open an image processing algorithm into a window
•
Move and resize an image window
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 2#User interface basics#z 4: Managing multiple image windows
•
Zoom and pan the image within the window
•
Manipulate multiple image windows on the screen
•
Close image windows
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Chapter 2#User interface basics#z 4: Managing multiple image windows
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3
Importing and
viewing an image
This chapter shows you how to import a digitized airphoto in TIFF format, and
how to display the dataset as a greyscale image and enhance the contrast. You learn
about the interface ER Mapper provides for creating and editing data view
algorithms (the Algorithm dialog).
About the algorithms concept
The goal of all image processing is to enhance your data to make it more
meaningful and help you extract the type of information that interests you. To
make this procedure faster and easier, Earth Resource Mapping developed a new
image processing technique called “algorithm data views.” Understanding how to
use algorithms is the key to understanding how to use ER Mapper effectively.
What is an algorithm data view?
An algorithm is a list of processing steps or instructions ER Mapper uses to
transform raw datasets on disk into a final, enhanced image on your screen display.
In this sense, algorithms let you define a “view” into your data that you can save,
reload, and modify at any time.
ER Mapper Workbook - Airphoto Mosaic Applications 49
Chapter 3#Importing and viewing an image#z About the algorithms concept
You use ER Mapper’s graphical user interface to define your list of processing
steps, and you can save the steps in an algorithm file on disk. An algorithm file can
store any of the following information about your processing:
•
Names of dataset(s) to be processed and displayed
•
Subsets of the dataset(s) to be processed (zoomed areas)
•
Bands (layers of data) in the dataset(s) to be processed
•
Color mapping and contrast enhancements (Transforms)
•
Filtering to be applied to the data (Filters)
•
Equations and combinations of bands or datasets used to create the image
(Formulae)
•
Color mode used to display the data (Pseudocolor, Red Green Blue, or Hue
Saturation Intensity)
•
Any vector datasets, thematic color, or map composition layers to be displayed over
the raster image data
•
Definition of a page size and margins (used for positioning the image on a page for
creating maps and printing)
•
Viewpoint and other parameters when viewing the image in 3D perspective
By being able to apply a set of processing steps as a single entity, the complexity
often associated with image processing is greatly simplified. In addition, you gain
tremendous savings in disk space, since you do not need to store intermediate
processed copies of your original data on disk.
Building Algorithms in ER Mapper
There are three primary ways to build a processing algorithm in ER Mapper:
•
Open a dataset directly (File Open) and have ER Mapper automatically display the
dataset using a simple default algorithm
•
Use the Algorithm dialog options to build an algorithm by adding the desired types
of layers, loading datasets, and specify processing steps for each layer.
•
Use image wizards to have ER Mapper automatically create any of several types of
specialized algorithms for you. In this case, ER Mapper adds the appropriate layers
to the Algorithm dialog, prompts you to load a dataset, and possibly other options
as well.
The majority of exercises in this workbook ask you to build algorithms from
scratch so you become familiar with and thoroughly understand the basic concepts.
However, you will also use the automatic algorithm creation wizards from time to
time to understand how they can save time.
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Chapter 3#Importing and viewing an image#z About the algorithms concept
Using Algorithms as Templates
Once you have saved your processing instructions as an algorithm file, you can use
the algorithm as a “template” to easily apply the same processing to other datasets.
To use an algorithm as a template, simply load the desired dataset(s) to replace the
default dataset(s) saved with the algorithm, and click GO to apply the same
processing to the new dataset(s). You may also need to adjust the transforms (color
mapping) for the new datasets.
Any algorithm can be used as a template, and ER Mapper also provides many
template algorithms for common tasks. These include common display techniques
(pseudocolor, colordrape, etc.), writing processed image files to disk, and saving
algorithms as “Virtual Datasets.”
The Algorithm dialog
The Algorithm dialog is a special dialog box that serves as your “command
center” for creating and editing algorithms in ER Mapper. To open the Algorithm
dialog, you can select Algorithm... from the View menu or click the Edit
Algorithm
toolbar button. The key components of the Algorithm dialog are
labelled below and described in the table that follows.
view mode (2D or 3D)
tab pages to select categories of options for
layer or surface (Layer tab page is selected)
menu to add
or change
layers/surfaces
surface
list of layers
in surface
process diagram
for selected
layer
data
structure
diagram
panel
Data structure diagram Shows a list of surfaces and layers contained in the
current algorithm using a hierarchy or “tree” structure.
Select (click on) a surface or layer change its options
using the Tab pages.
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Chapter 3#Importing and viewing an image#z About the algorithms concept
Surface
A group of raster and/or vector data layers that combine
to create a view or image. A single algorithm can have
multiple surfaces that become independent entities when
viewed in 3D mode.
Layers
Components of a surface that contain data used to
construct an image. Different layer types can contain
raster or vector data, and processing for each layer is
controlled independently from the others.
View Mode
Sets the manner in which data is displayed as two
dimensions (2D) normal or page layout, or three
dimensions (3D).
Tab pages
Display categories of options for controlling the image
display and processing techniques, such as Layer for
options for the current layer, or Surface for options that
apply to an entire surface.
Process diagram
Used to control the processing operations applied to
image(s) in the currently selected layer (displayed when
Layer tab is selected).
The Process Diagram
When the Layer tab is selected, the horizontal row of buttons on the right-lower
panel of the Algorithm dialog are called the process diagram. They are used to
define your image enhancement and processing operations for the currently
selected data layer. Each button in the diagram controls a specific image
processing function.
As the arrows indicate, the processing stream flows from left to right. Typically,
you may specify a dataset to be used, the bands within the dataset to be processed,
then apply processing using formulae, filters, transforms or other options to create
your desired image. When you select GO (from the toolbar or File menu),
ER Mapper compiles all the processing steps you specified and renders the
resulting image to the screen display. The name and function of the main
processing diagram buttons are as follows.
52
Button
Function
Load Dataset
Use to load a dataset from disk, or edit or view
information or comments about a dataset.
Band Selection
Use to select one or more bands in the dataset for use
in generating an image (a drop-down list).
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 3#Importing and viewing an image#z Hands-on exercises
Button
Function
Formula
Use to enter, load, or save a formula to perform image
algebra and other arithmetic operations.
Filter
Use to add or delete one or more spatial filters. (There
are both pre- and post-formula Filter buttons.)
Transform
Use to adjust image contrast and brightness. (There
are both pre- and post-formula Transform buttons.)
Sun Angle
Use to specify sun angle illumination of the image to
create shaded relief effects.
Note: A cross or “X” through the button indicates that the function is not active in the
current data layer. In addition, there are other buttons for some layer types that you
will learn about later in this manual.
Hands-on exercises
These exercises show you how to import a digitized airphoto into ER Mapper,
display and enhance the image in greyscale, and save and reload a simple image
processing algorithm.
What you will
learn...
Before you
begin...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Import a digitized airphoto into ER Mapper
•
Load and display the imported dataset as a greyscale image
•
Use the Algorithm dialog to define a simple processing algorithm
•
Change the color lookup table used to display the image
•
Use transforms to adjust the image contrast
•
Add text labels and comments to an algorithm
•
Save the processing algorithm to disk
•
Reload and view the saved algorithm
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
ER Mapper Workbook - Airphoto Mosaic Applications 53
Chapter 3#Importing and viewing an image#z 1: Opening an airphoto image file
1: Opening an airphoto image file
Objectives
Learn to import a airphoto image from an external file to create a new image
dataset in ER Mapper format.
Note: The sample airphoto applications training datasets must be installed on your
computer before you can complete this exercise. See Appendix A if needed for
more information.
About imputting data
You can open any of the following image data formats directly into ER Mppaer
without having to import them as ER Mapper Raster Datasets:
•
ER Mapper Algorithm (.alg)
•
ER Mapper Raster Dataset (ers)
•
ER Mapper Compressed Image (.ecw)
•
Vector Map (.erv)
•
Windows Bitmap (.bmp)
•
ESRI BIL and GeoSPOT (.hdr)
•
GeoTIFF/TIFF (.tif)
•
JPEG (.jpg)
•
USGS DOQQ (Grayscale)
•
RESTEC/NASDA CEOS (.dat)
Opening a TIFF image
To open a TIFF image in ER Mapper, click on the Open
Standard toolbar.
Open button
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button on the
Chapter 3#Importing and viewing an image#z 1: Opening an airphoto image file
In the Open dialog box, select ‘GeoTIFF/TIFF(.tif)’ from the Files of Type list,
and then select the TIFF image to be opened in ER Mapper.
You can add TIFF images to Algorithms and perform most image enhancements
on them. ER Mapper adds a header file with a .ers extension to hold statistical
information about the image.
The Geocoding Wizard will only rectify ER Mapper Raster Dataset images. If you
want to rectify a TIFF image you must either save it as an ER Mapper Raster
Dataset or originally import it as an ER Mapper Raster Dataset.
Importing a TIFF image
To import a dataset from an external file into ER Mapper, you will use the import
programs listed under the Utilities menu in ER Mapper. In this case, you will
import an airphoto that has previously been converted to a digital format by
scanning and saved as a TIFF format graphics file. When you import a dataset into
ER Mapper, it creates two files: and binary data file (in Band Interleaved by Line
or “BIL” format), and an ASCII header file with a “.ers” file extension:
Utilities
airphoto.tif
Import Graphics formats
Raster Translated Images
(scanned raster
airphoto file)
airphoto
(ER Mapper BIL data file)
airphoto.ers
(ER Mapper ASCII
header file)
TIFF (.tif)
Open the TIFF import dialog
1 From the Utilities menu, select Import Graphics formats, then select
Raster Translated Images, then Import.
The Import Raster_Translated dialog box opens. This dialog lets you specify
the name of the input file to be imported, and the name of the ER Mapper dataset
to be created. All image formats that can be opened directly in ER Mapper are
imported via this dialog bax.
2 Click the file chooser
Name field.
button on the right side of the Import File/Device
The Input File Selection dialog box opens.
3 In the Files of Type: field, select ‘GeoTIFF/TIFF(.tif)’.
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Chapter 3#Importing and viewing an image#z 2: Displaying an image in greyscale
4 From the Directories menu (on the Input File dialog), select the path
ending with \examples.
5 Double-click on the directory named ‘Shared_Data’ and then the directory
named ‘airphoto_training.’
6 Double-click on the image file named ‘photo_86.tif’ to load it.
7 Click the file chooser
button next to the Output Dataset Name field.
The Output Dataset Selection dialog box opens.
8 From the Directories menu (on the Output Dataset dialog), select the
path ending with \examples.
9 Double-click on the directory named ‘airphoto_training.’
10 In the Save As: field, enter the text raw_photo_86 then click OK.
11 Click OK on the Import TIFF dialog.
ER Mapper reads the TIFF file and begins creating a dataset in ER Mapper format.
12 When the import finishes, click OK on the confirmation dialog, then click
Cancel on the Import Raster_Translated dialog.
In this case, ER Mapper translated the TIFF image data and created two files:
•
‘raw_photo_86’ (the binary data file)
•
‘raw_photo_86.ers’ (the ASCII header file)
2: Displaying an image in greyscale
Objectives
Learn to open an image window and the Algorithm dialog, load an image, and
display the image in greyscale. You will also learn to change the contrast (color
mapping) of the image.
Note: The airphoto you imported is a color photograph. You will initially learn to view
and adjust the photo as a greyscale image, which is appropriate for black and white
aerial photographs. Later you will learn to view it as an RGB color image (in the
following chapter).
Open an image window and the Algorithm dialog
1 From the View menu, select Algorithm....
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Chapter 3#Importing and viewing an image#z 2: Displaying an image in greyscale
A new empty image window opens in the upper-left corner of the screen, and the
Algorithm dialog opens.
Note that the Algorithm dialog shows a default surface with one Pseudocolor
layer in the left-hand panel (labelled “Pseudo Layer”), and a process diagram for
that layer in the right-hand panel. The words “No Dataset” above the process
diagram indicate that no dataset is currently loaded into the layer.
Note: If you open the Algorithm dialog when no image windows are currently open (as
in this case), ER Mapper opens an empty image window for you automatically.
This shortcut saves you the step of opening a window.
Load the airphoto dataset into the Pseudo layer
1 In the Algorithm dialog, click the Load Dataset
button..
Load Dataset button
The Raster Dataset file chooser dialog box appears.
2 From the Directories menu (on the Raster Dataset dialog), select the path
ending with \examples.
The scrolling list in the center now shows a list of directories containing example
images supplied with ER Mapper .
3 Double-click on the directory named ‘airphoto_training.’
A list of raster datasets with the file extension “.ers” are displayed. (If you do not
see files with an .ers extension, open the Files of Type menu and select
‘ER Mapper Raster Dataset (.ers).’)
4 Double-click on the dataset named ‘raw_photo_86.ers’ to load it.
The file chooser dialog closes, and the dataset is loaded into the Pseudo layer. Note
that the dataset name (‘raw_photo_ap.ers’) now appears above the process
diagram.
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Chapter 3#Importing and viewing an image#z 2: Displaying an image in greyscale
Note: To load an ER Mapper format raster dataset, you must select the “.ers” header file,
not the binary data file without the .ers extension.
Change the color table to view the image in greyscale
When you are using the Color Mode named Pseudocolor (as you are in this
example), the Color Table controls the set of colors ER Mapper uses to display the
image. If your airphoto is black and white airphoto, you should normally choose to
view it as greyscale image. (RGB color images are discussed in the next chapter.).
1 In the Algorithm dialog, select the Surface tab.
Select Surface tab
Options for Color Mode, Color Table, and Transparency now appear in the
panel.
Color Mode is set to “Pseudocolor” meaning that a color lookup table (LUT) is
used to control the image colors. The current color table is the last one selected in
ER Mapper (‘pseudocolor’ in the above diagram).
2 Click on the Color Table drop-down list button.
A menu listing available color lookup tables appears.
3 Click on the lookup table named greyscale.
ER Mapper renders the image using a greyscale color table that has colors from
black to white with grey shades in between. The brightest features in the airphoto
are shown in light tones, darkest features in dark tones.
Note: ER Mapper has many other color tables that are used for different types of data.
For black and white airphotos, you will usually use ‘greyscale.’
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Chapter 3#Importing and viewing an image#z 3: Selecting bands and adjusting contrast
3: Selecting bands and adjusting contrast
Objectives
Learn to view different bands in the dataset and use the Transform dialog
options to adjust the image contrast. Also learn about image histograms.
Select the Layer tab in the Algorithm dialog
1 In the Algorithm dialog, select the Layer tab.
Select Layer tab
The contents of the right side of the Algorithm dialog change to show the process
diagram option buttons.
2 If needed, drag one side of the Algorithm dialog to widen it until you can
see all the option buttons above.
Tip:
When you resize or reposition a dialog box, ER Mapper automatically remembers
this the next time you open it. This lets you setup your work environment as you
like.
Display the histogram for the Red band
Color airphotos are usually divided into red, green and blue components during the
digitizing (scanning) process. This creates three layers of data, each called a
“band” in ER Mapper. Notice that the Band Selection list in the Algorithm dialog
shows that the Red band (band 1 of 3) is currently selected.
1 In the Algorithm dialog, click on the right-hand Edit Transform Limits
button (blue) in the process diagram.
Edit Transform Limits button
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Chapter 3#Importing and viewing an image#z 3: Selecting bands and adjusting contrast
The Transform dialog box opens showing a histogram of the data values in the
current band (Red in this case), and options for modifying the image contrast.
transform line
color bar showing
colors in current
Color Table
(greyscale)
histogram of
red band values
actual range of
values in red band
A histogram is a graphical display of the relative frequency distribution of values
in an image. In this case, most of the data values occur in the middle part of the 0
to 255 data range possible for digitized airphoto datasets. Peaks in the histogram
show where there are many pixels with similar data values, and sometimes indicate
identifiable features in an image. The shape of this histogram indicates that most
pixels have mid-range brightness values (the peak in the histogram), with many
fewer pixels either very bright or dark (the right and left sides of the histogram).
The “Actual Input Limits” field shows the actual range of values in the current
band of the dataset. In this case, the red band values fill the possible dynamic range
of zero to 255.
2 Drag the Transform dialog left underneath the image window (so you can
see the options on the Algorithm dialog).
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Display the Green band of the airphoto
1 In the Algorithm dialog, click on the Band Selection drop-down list and
select B2:Green.
select green band
ER Mapper redisplays the image in the window, this time showing the green band
in the airphoto dataset.
The Transform dialog now shows a histogram of the green band data values.
Notice that the ‘Actual Inputs Limits’ at the bottom shows a range of 16-255, so
band 2 (green) does not contain any values between 0-15.
Display the Blue band of the airphoto
1 In the Algorithm dialog, click on the Band Selection drop-down list and
select B3:Blue.
select blue band
ER Mapper displays the blue band data in the image window, which is noticeably
brighter that the red or green bands.
On the Transform dialog, notice that the ‘Actual Inputs Limits’ shows a range of
approximately 48-255, so band 3 (blue) does not contain any values between 0-47.
(This is also indicated by the shape of the histogram, with the left side being
empty.)
Each band in a color airphoto usually has its own unique histogram, caused by
differences in the amount of red, green and blue light reflected by objects on the
ground. (This will be discussed more later.)
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Chapter 3#Importing and viewing an image#z 3: Selecting bands and adjusting contrast
Adjust the contrast to use the entire range of colors
By default, there is a linear mapping between the input data values and the output
colors used to display them. Since the blue band has no values between 0-44, the
darker grey shades in the greyscale color table are not used in the image (thus it
appears very bright).
1 From the Limits menu (on the Transform dialog), select Limits to Actual.
The X axis data range fields (below the histogram) change to match the Actual
Input Limits values.
ER Mapper renders the image again, this time mapping only the range of values
that actually occurs in the blue band image (48-255) to the full range of grey tones
to display the image. This creates better overall contrast between the light and dark
areas. Notice also that the histogram has widened slightly to better fill the
histogram window area.
Apply a linear lightening effect to the image
1 As shown in the diagram below, drag the circled part of the dashed
transform line up to the left until it is flush with the left-hand vertical axis.
display (color) range
0
255
100
48
255
input data values
ER Mapper applies the change and the image lightens. As shown in the right-hand
diagram (above), you have adjusted the transform line to exclude values of about
0-100 on the display (vertical) axis, which correspond to the darker shades of grey
in the greyscale lookup table. Now the entire 48-255 range of data on the X
(horizontal) axis is mapped to only the lighter shades of grey in the greyscale
lookup table, causing the image to appear lighter.
Also notice that a second unfilled histogram appears in the window. This is the
output histogram, and it represents the distribution of colors in the image. (It is
different to the input histogram because you changed the color mapping by
adjusting the transform line.)
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2 On the Transform dialog, click the Create default linear transform
button.
Create default linear
transform button
ER Mapper returns the transform line to its default position and redisplays the
image. (The default position is a straight linear transform, where the line’s X
position is equal to its Y position. This also makes the output histogram the same
as the input histogram, so it is no longer visible.)
Apply a linear darkening effect to the image
1 As shown in the diagram below, drag the circled part of the dashed
transform line down to the right along the right-hand vertical axis.
200
display (color) range
0
200 255
45
255
input data values
ER Mapper applies the change and the image darkens. As shown in the right-hand
diagram, you have adjusted the transform line to exclude values of about 200-255
on the display (vertical) axis, which correspond to the lighter shades of grey in the
lookup table. Now the entire 0-255 range of data on the X (horizontal) axis is
mapped to only the darker shades of grey, causing the image to appear darker.
Also notice that the linear darkening effect caused the output histogram to shift
left, showing that predominantly darker grey shades are used in the image.
2 Click on the Create default linear transform
button.
The transform line returns to its default position and the image redisplays.
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Apply a linear contrast stretch to increase image contrast
1 Point to the base of the left side of the histogram (at the bottom of the
slope).
The X-Y coordinate location of the cursor displays below ‘Histogram Style.’ Note
that the first (X) value is about 80-85. Even though the lower limits of the band 3
values are 45, there are very few values between 45 and 85 (as indicated by the
frequency shown in the histogram).
2 Adjust the transform line down to move it the base of the left side of the
histogram as shown in the diagram below.
0
0
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ER Mapper Workbook - Airphoto Mosaic Applications
display or LUT range
255
85
data values
255
Chapter 3#Importing and viewing an image#z 3: Selecting bands and adjusting contrast
ER Mapper applies the change and the image contrast increases. Now the contrast
between light and dark parts of the image is enhanced, making spatial features
easier to visually interpret. In this case, you adjusted the transform line to map data
values of about 85-255 on the horizontal axis to the entire range of grey shades.
Any value less than 85 is mapped to the darkest color (black).
This mapping better utilizes the dynamic range of grey shades in the lookup table,
which improves image contrast. (This effect is often called histogram clipping
because it clips the tail off the histogram.)
3 Click on the Create default linear transform
button.
The transform line returns to its default position and the image redisplays.
Apply a 99% clip transform to the data
1 On the Transform dialog, click the Create autoclip transform
button.
Create autoclip transform button
ER Mapper automatically sets the transform line into a position that clips off one
percent of the data values (0.5% from the low end and 0.5% from the high end).
This is called “autoclipping” since ER Mapper analyzes the histogram for the
current dataset band and automatically positions the transform line for you.
Autoclipping is the most commonly used contrast enhancement technique for
airphoto datasets, and you will use it throughout the rest of this workbook.
Tip:
You can set the percentage used for the autoclip function by double-clicking on the
button. Values between 90 and 99.5 are usually used. Lower values create
stronger contrast, but also saturate more of the brightest and darkest features. The
default is 99 percent.
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Chapter 3#Importing and viewing an image#z 3: Selecting bands and adjusting contrast
Apply a Histogram equalize transform to the data
1 On the Transform dialog, click the Histogram equalize
button.
Histogram equalize button
Tip:
Pass the mouse over the button to see the button name (tooltip).
ER Mapper creates a complex piecewise linear transform line and updates the
image. Notice that in this case the overall contrast is maximized, but detail may be
obscured (saturated) in the brightest and darkest features.
Histogram equalization (also called uniform distribution stretching) automatically
adjusts the transform line so that image values are assigned to display levels based
on their frequency of occurrence. More display values are assigned to the most
frequently occurring portion of the histogram, so the greatest contrast
enhancement occurs in the data range with the most values (peaks in the
histogram). Histogram equalization tries to create and approximately equal
number of each color in the image, and usually creates an image with very strong
contrast. In some cases, it can also saturate areas which can obscure detail.
Apply a Gaussian equalize transform to the data
1 On the Transform dialog, click the Gaussian equalize
button.
Gaussian equalize button
ER Mapper creates a complex piecewise linear transform line (sometimes with
slight stair steps) and updates the image.
Gaussian equalization automatically adjusts the transform line so that image
values are assigned as needed to make the output (display) values occur with a
Gaussian distribution. A Gaussian, or “normal” distribution, is characterized as
producing a bell-shaped histogram (shown in the output histogram.)
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Gaussian equalization is useful when data is skewed in such a way that features
could be abnormally saturated if stretched linearly (such as with an autoclip). This
technique tends to bring out more detail in areas with less frequently occurring
data values so it is good for emphasizing subtle features.
Tip:
You can set the number of standard deviations used for the Gaussian equalize
function by double-clicking on the
button. Smaller values produce more
contrast and higher values less contrast. The default is 3 standard deviations.
2 On the Transform dialog, click Create default linear transform
.
3 Click Close on the the Transform dialog to close it.
Use 99% Contrast Enhancement button
Up until now you have learned to manually adjust the image contrast by using the
options on the Transform dialog because it is important to understand them. Now
you will learn to use a faster, easier way to adjust the image contrast.
1 In the Algorithm dialog, click on the Band Selection drop-down list and
select B2:Green.
select green band
2 On the main ER Mapper menu, click the 99% Contrast Enhancement
button.
99% Contrast Enhancement
button
ER Mapper runs the algorithm again to display the green band of the airphoto, and
automatically adjusts the contrast for you. This button performs the following
sequence or actions for you automatically:
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Chapter 3#Importing and viewing an image#z 4: Labelling and saving the algorithm
Process->Limits to Actual->Process->99% autoclip->Process
3 In the Algorithm dialog, click on the Band Selection drop-down list and
select B1:Red.
4 On the main ER Mapper menu, click the 99% Contrast Enhancement
button.
ER Mapper runs the algorithm again to display the red band of the airphoto, and
automatically adjusts and optimizes the contrast for you.
Tip:
, 99% Contrast Enhancement
The Refresh
and STOP
buttons
are located on both the main menu and the Algorithm dialog. The STOP button
ceases all processing so you don’t have to wait for the processing to finish if you
make a mistake.
4: Labelling and saving the algorithm
Objectives
Learn to specify description labels, titles, and comments for an algorithm, and
save the algorithm processing steps to a file so you can view it later.
In order to save your image and view it later, you need to save the processing steps
you defined previously as an algorithm file on disk. Note that you are not creating
a new image file, you are only saving a text description of the steps required to
enhance your original airphoto image.
Enter a description for the Pseudo layer
1 In the Algorithm dialog, click on the text “Pseudo Layer” in the left-hand
panel.
click to make
text field editable
The text become reverse highlighted (shown above) indicating the text is selected.
2 Type the text airphoto red band in the field. Then press the Enter or
Return key on your keyboard.
This text now becomes a visual description for the layer.
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Chapter 3#Importing and viewing an image#z 4: Labelling and saving the algorithm
Note: If a layer is not already selected (highlighted), click once on the layer to select it,
then click a second time on the text label to make it editable.
Enter a description for the entire algorithm
1 In the Algorithm dialog, select the text in the Description text field (it
currently reads ‘No Description’).
(To select the text, either drag through it, or triple-click to select the entire line.)
2 Type the following text, then press Enter or Return on your keyboard:
San Diego airphoto 86 in greyscale
This text now becomes a brief description for the entire algorithm.
Save the processing steps to an algorithm file on disk
1 From the File menu (on the main menu), select Save As....
The Save Algorithm file chooser dialog opens.
2 From the Directories menu, select the path ending with the text
\examples. (The portion of the path name preceding it is specific to your
site.)
3 Double-click on the directory named ‘airphoto_training’ to open it.
4 In the Save As: text field, click to place the cursor, then type the following
name for the algorithm file:
Airphoto_86_greyscale
5 Click the Apply button to save the algorithm and leave the dialog open.
Your pseudocolor greyscale algorithm is now saved to an algorithm file on disk.
Add comments to the algorithm
1 On the Save Algorithm dialog, click the Comments... button.
A dialog box appears titled with the algorithm path and file name, and a text area
to type comments about your algorithm. The cursor is already active.
2 In the comments dialog, type the following information to describe your
algorithm:
This algorithm displays the red band of Tustin airphoto 86
as a greyscale algorithm. A 99% autoclip transform is used
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Chapter 3#Importing and viewing an image#z 5: Reloading and viewing the algorithm
to increase image contrast.
3 Click OK on the comments dialog to save your comments.
4 Click Cancel on the Save Algorithm dialog close it.
5: Reloading and viewing the algorithm
Objectives
Learn to reload and display the algorithm you just created.
Open a second image window
1 On the Standard toolbar (on the main menu), click the New Image
Window
button.
ER Mapper opens a new image window (this is a shortcut for selecting New from
the File menu). Drag the new window to the lower left part of the screen (so you
can see all or most of the other image window).
Open the greyscale algorithm you created earlier
1 On the main menu, click on the Open
button.
The Open file chooser dialog appears. (This is a shortcut for selecting Open...
from the File menu.)
2 From the Directories menu, select the path ending with the text
\examples.
3 From the Files of Type: list, select ‘ER Mapper Algorithm (.alg)’.
4 Double-click on the directory named ‘airphoto_training’ to open it.
Your ‘Airphoto_86_greyscale’ algorithm name should appear in the list.
5 Click once on your algorithm name to highlight it (do not double-click).
6 Click the Apply button to load and process the algorithm without closing
the Open dialog box.
ER Mapper runs the algorithm and displays the enhanced airphoto dataset in the
image window. It looks identical to the other image since they both use the same
algorithm and dataset.
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Chapter 3#Importing and viewing an image#z 5: Reloading and viewing the algorithm
View the algorithm comments
1 On the Open dialog, click the Comments... button.
The dialog box opens showing the comments you entered for your algorithm.
These comments can be very helpful to others who use or display your algorithm,
and they are a good way to document the procedures you used to create it.
2 Click Cancel on the comments dialog box to close it.
Close both image windows and the Algorithm dialog
1 Close the lower image window:
•
For Windows, click the
Close button in the upper-right window corner.
2 Close the other image window by repeating Step 1.
3 On the Algorithm dialog, click the Close button.
Only the ER Mapper main menu is now open on the screen.
What you
learned...
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Import a digitized airphoto into ER Mapper
•
Load and display the imported dataset as a greyscale image
•
Use the Algorithm dialog to define a simple processing algorithm
•
Change the color lookup table used to display the image
•
Use transforms to adjust the image contrast
•
Add text labels and comments to an algorithm
•
Save the processing algorithm to disk
•
Reload and view the saved algorithm
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Chapter 3#Importing and viewing an image#z 5: Reloading and viewing the algorithm
72
ER Mapper Workbook - Airphoto Mosaic Applications
4
Viewing an image
in RGB
This chapter shows you how to display an airphoto dataset as an RGB color
composite image. You also learn how to manipulate layers on the Algorithm
dialog, and how to use wizards for viewing datasets and creating RGB algorithms.
About RGB color images
In the RGB color system, each color is created by mixing different proportions of
the three additive primary colors–red, green and blue. Computers create color by
lighting up an array of tiny red, green and blue phosphors on the screen.
For example, to create a green pixel on the screen, the green phosphor for that
pixel is lit up to its full intensity, and the red and blue phosphors are essentially
turned off. (This might be a park or golf course for example.) To create a yellow
pixel, the red and green phosphors are set to full intensity and the blue is turned
off. (Red and green together combine to create yellow in the RGB color system.)
By combining various proportions of the three additive primary colors, nearly any
color can be created. When all three phosphors are lit to their full intensity white is
created, when all are turned off black results. When red, green and blue occur in
equal proportions, grey is produced.
ER Mapper Workbook - Airphoto Mosaic Applications 73
Chapter 4#Viewing an image in RGB#z Hands-on exercises
Scanning and display of color aerial photography
Natural color airphotos record reflected light in the same wavelengths as the
human eye can perceive–red, green and blue. Color infrared (CIR) airphotos are
sensitive to the red and green wavelengths (not blue), but also to the near infrared
wavelengths (which are beyond the range of human vision).
When color airphotos are digitized (scanned), the resulting digital file is divided
into red, green and blue components called bands. Each band can have a possible
data value range of 0 to 255 (8 bits). For example, a pixel in the digital image that
is green (grass for example) has a high value in the green band (perhaps 200), and
relatively low values in the red and blue bands (perhaps 70).
To display a color airphoto on a computer screen, the red band of the image file is
loaded into the red display plane of the computer (which controls the red
phosphors), the green band into the green color plane, and the blue band into the
blue plane. These combine to create a single RGB color composite image on the
screen, which looks the same as the original printed airphoto.
original
color print
scanning
process
ER Mapper
layers
red layer
red
color
airphoto
color image
display
green
blue
band
image
green layer
RGB color
composite
blue layer
Hands-on exercises
These exercises show you how to display a color airphoto dataset as an RGB color
composite image, understand how to use red, green and blue layers in an
algorithm, and use image wizards to create RGB algorithms.
What you will
learn...
74
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Open a dataset directly and have ER Mapper create a display algorithm
•
Understand the red, green and blue layers in an RGB algorithm
•
Delete, add and change layers in an algorithm
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 4#Viewing an image in RGB#z 1: Creating RGB algorithms
•
Before you
begin...
Use transforms to adjust the RGB color contrast
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
1: Creating RGB algorithms
Objectives
Learn to open a dataset directly and have ER Mapper automatically create a
simple display algorithm for it. Also learn to use the Image Display and
Mosaic Wizard.
In the previous exercise, you created an algorithm manually by loading a dataset
into the Algorithm dialog and adjusting the contrast using the Transform dialog
options. This was necessary to introduce you to basic concepts of loading and
displaying datasets. Now you will learn to use ways to automate the creation of
algorithms.
Open and display the sample airphoto dataset
1 On the main menu, click the Open
button.
An image window and the Open dialog box appear.
2 From the Directories menu (on the Open dialog), select the \examples
path.
3 Double-click on the ‘airphoto_training’ directory to open it.
The Open dialog can be set to display files with certain extensions, or all files. In
previous exercises, you have used the Open dialog to open algorithm (.alg) files.
4 From the ‘Files of Type’ drop-down list, select ER Mapper Raster Dataset
(.ers).
The contents now show only files with “.ers” file extensions.
5 Click once on the ‘raw_photo_86.ers’ dataset, then click the Apply button.
ER Mapper automatically loads the dataset and creates a simple RGB color
composite algorithm. This procedure is a fast way to view any dataset. (If you have
many datasets to view, select them in the Open dialog and click Apply. Clicking
OK closes the dialog.)
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Chapter 4#Viewing an image in RGB#z 1: Creating RGB algorithms
Note: If the dataset has only one band (such as a black and white airphoto), ER Mapper
creates a greyscale algorithm similar to the one you created earlier.
6 On the Open dialog, select ‘ER Mapper Algorithm (.alg)’ from the Files of
Type drop-down list.
7 Click Cancel on the Open dialog to close it.
The default file type will be “.alg” the next time you open it. (This is
recommended to simplify these exercises.)
8 Select Close from the File menu to close the image window.
Use the Image Display and Mosaic Wizard
1 On the Common Functions toolbar, click the Image Display and Mosaic
Wizard
button.
click to create
algorithm
The Select files to display and mosaic page of the Image Display and
Mosaic Wizard opens
2 Click the Load Image
button.
The Select File dialog opens.
3 From the Directories menu (on the Select File dialog), select the
\examples path.
4 Double_click on the ‘Applications’ directory to open it.
5 Double_click on the ‘Airphoto’ directory.
6 Open the ‘3_Balancing’ directory.
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Chapter 4#Viewing an image in RGB#z 1: Creating RGB algorithms
7 Double-click on the image dataset ‘ADAR_Del_Mar_1.ers’ to select it.
This dataset is a high resolution image covering a portion of Del Mar, California
near San Diego. This dataset is a multispectral image acquired by the ADAR 5000
system mounted on an aircraft. The data values represent reflectance of light in
three different wavelengths (similar to a multispectral satellite image).
8 Select the following options on the wizard page:
Display image in 2D
Image will be displayed in a 2D mode.
Manually set display method
Enables you to set how the image is to be displayed. If
you do not select this option, the wizard will set the
display method.
9 Click on the Next > button to go to the next dialog box.
The wizard will open the Select display method dialog box for you to specify
the display method.
Select display method.
You have the choice of four different display methods:
Greyscale
Loads a single band into a pseudocolor layer using the
greyscale Color Table.
Red Green Blue
Loads three of the bands into RGB layers.
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Chapter 4#Viewing an image in RGB#z 1: Creating RGB algorithms
Sunshade
Loads a single band into a greyscale pseudocolor layer
with sun-shading enabled.
Colordrape
Drapes a pseudocolor layer over an intensity layer with
the sun-shading enabled.
10 Select the Red Green Blue option and Manually select display method
properties to specify how the image is to be displayed.
11 Click on the Next > button to go to the next dialog box.
Select display method
The Select How to display using Red Green Blue wizard dialog box allows
you to select the image bands that are to be displayed as Red Green and Blue.
12 In the Type: field, select ‘RGB 123’ so that bands 1, 2 and 3 of the image
will be displayed as Red, Green and Blue respectively.
13 Click on the Next> button to go to the final dialog box.
The wizard will process the image and display it with the transform clip limits set
to 99%.
14 In the Image Display and Mosaicing Wizard has finished dialog box,
select Finish to close the wizard, or one of the options to change the
displayed image.
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Chapter 4#Viewing an image in RGB#z 2: Working with algorithm layers
2: Working with algorithm layers
Objectives
Learn to turn data layers on to include them in processing and off to exclude them
from processing. Also learn how to move layers, add layers to an algorithm, and
understand the concept of Red Green Blue (RGB) algorithms.
Select layers in a surface
In ER Mapper, a surface is a group of layers that combine to create an image on
the screen. Surfaces and layers are shown in the data structure diagram on the left
side of the Algorithm dialog. Each surface has one or more layers that can be
raster data (such as a scanned airphoto) or vector data (such as a vector GIS
overlay of roads).
1 On the main menu, click the Edit Algorithm
Algorithm dialog box.
button to open the
2 On the Algorithm dialog, click on the Green layer to select it
click to select - process diagram applies to selected layer
When you select a layer, the process diagram on the right side shows the
processing options that pertain to that layer. For example, if you wanted to change
the contrast (transform) of the data in the Green layer, you would first select the
Green layer and then click the
button in the process diagram.
3 Hold down the Shift key and click on the Blue layer.
Both the Green and Blue layers are now selected, so you see two process diagrams
on the right side.
Note: The layer labels ‘Red Layer,’ ‘Green Layer,’ and so on were added by ER Mapper
automatically when it created the RGB algorithm. As shown in the previous
exercise, you can change the labels to any text desired by clicking on the text when
the layer is selected.
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Chapter 4#Viewing an image in RGB#z 2: Working with algorithm layers
Contract and expand the surface diagram
1 Click once on the small “-” (minus sign) button next to the surface name
‘[RGB]:RGB 123.’
The layers are contracted into the surface, and all of their process diagrams are
shown on the right side. (This can be useful when working with algorithms that
have many surfaces and layers.)
2 Click once on the small “+” (plus sign) button next to the surface name.
All three layers are again expanded and shown in the tree structure diagram under
the surface name.
Turn layers on and off to see the effect
1 On the Algorithm dialog, right-click on the Red layer, and select Turn Off
from the shortcut menu.
right-click, then
select Turn Off
The Red layer becomes dim to indicate that it is turned off.
2 Right-click on the Blue layer, and select Turn Off.
The Blue layer becomes dim to indicate that it is turned off.
ER Mapper displays only the green component of the image (band 2 of the
scanned airphoto) because the Blue and Red layers of the algorithm are turned off.
Any layers that are turned off are ignored during processing.
3 Right-click on the Red layer again, and select Turn On.
ER Mapper displays the red (band 1) and green (band 2) components of the image.
(The image looks yellow because combining red and green creates yellow in the
RGB color system.)
4 Right-click on the Blue layer again, and select Turn On.
ER Mapper displays all the image bands again, so you see a full color image.
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Chapter 4#Viewing an image in RGB#z 2: Working with algorithm layers
Change the order of layers by moving them
You can move layers up or down relative to each other by dragging and dropping
them, or by selecting them and using the Move Up and Move Down buttons.
(Layer order can be important in mosaic algorithms as you will learn later.)
1 Point to the blue icon next to the text “Blue Layer” and drag it up above the
Red Layer..
The Blue layer moves to the top of the layer list. You can move layers by dragging
and dropping them.
2 Click once on the Red Layer to select it, then click the Move Up
button.
2-click Move Up
1-select Red layer
The Red layer moves up one position to the top of the list.
3 Click once on the Blue Layer to select it, then click the Move Down
button.
The Blue layer moves down one position to the bottom of the list.
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Chapter 4#Viewing an image in RGB#z 3: Loading, adding and changing layers
3: Loading, adding and changing layers
Objectives
Learn to load a dataset into a specific layer or set of layers in an algorithm. Also
learn to add and delete layers, change the layer type, and change the algorithm
Color Mode.
Load a different dataset into all three layers
One of the great advantages of the ER Mapper’s algorithm concept is that any
algorithm can be used as a “template” to apply the same processing to another
dataset. You simply need to load the new dataset.
1 In the process diagram, click on the Load Dataset
button.
The Raster Dataset file chooser appears. Move it left so it does not cover the
Algorithm dialog.
2 From the Directories menu, select the path ending with the text
\examples.
3 Double-click to open the directory named ‘Shared_Data.’
4 Click once on the dataset named ‘Airphoto.ers.’
5 Click the Apply button.
The dataset is loaded into all three layers in the algorithm.
ER Mapper displays an airphoto of downtown San Diego, California as an RGB
color composite image. This demonstrates that you can open any existing RGB
algorithm and simply load a different dataset to view in RGB also.
6 On the main ER Mapper menu, click the 99% Contrast Enhancement
button to improve the image contrast.
About the OK and Apply buttons
82
•
If all three layers contain the same dataset (as in this case), Apply and OK load the
new dataset into all three layers automatically. (Apply and OK are the same except
that Apply leaves the dialog open and OK closes it.)
•
If you want to load a dataset into only the currently selected layer, use Apply this
layer only or OK this layer only. This is often useful when creating mosaic
algorithms as you will see later. (Apply this layer only and OK this layer only
are the same except that the first leaves the dialog open and the other closes it.)
•
Double-clicking on a dataset name in the file chooser is the same as clicking OK.
ER Mapper Workbook - Airphoto Mosaic Applications
Chapter 4#Viewing an image in RGB#z 3: Loading, adding and changing layers
Delete the Blue and Green layers
The following exercise is designed to familiarize you with building an RGB
algorithm by deleting, adding and duplicating layers, loading datasets, and
selecting bands. Although much of this is automated in ER Mapper, it is important
to understand how it works.
1 Click on the Blue layer to select it.
2 Click the Cut
button.
select Blue layer, then Cut
The Blue layer is deleted from the layer list.
3 Click on the Green layer to select it.
4 Click the Cut
button to delete the Green layer from the list.
ER Mapper displays only the red component of the image (airphoto band 1 in this
case) because the Blue and Green layers of the algorithm were deleted.
Restore the Green layer by adding one and loading the dataset
1 From the Edit menu, select Add Raster Layer, then select Green.
A new Green layer is added to the algorithm. New layers have no dataset loaded
(indicated by “No Dataset” above the process diagram), so it is dimmed (off).
2 In the process diagram, click the Load Dataset
button.
The Raster Dataset file chooser appears.
3 From the Directories menu, select the path ending with the text
\examples.
4 Double-click on the directory named ‘Shared_Data.’
5 Double-click on the dataset named ‘Airphoto.ers’ to load it and close the
dialog.
ER Mapper loads the dataset into the new Green layer and turns it on.
ER Mapper Workbook - Airphoto Mosaic Applications 83
Chapter 4#Viewing an image in RGB#z 3: Loading, adding and changing layers
Also note that band 1 is loaded in the Green by default in the process diagram. You
will need to select band 2 (green) for this layer to recreate the original RGB color
composite.
Note: If you had wanted to load this dataset into only the Green layer, you could have
clicked OK this layer only or Apply this layer only.
6 From the Band Selection drop-down list, select B2:Green.
You have now created a new Green layer that contains the same dataset and band
as the original green layer you deleted earlier.
Restore the Blue layer by duplicating the Green layer
1 With the Green layer still selected, click the Duplicate
button.
click Duplicate
A second Green layer is added below the first one. The second Green layer is an
exact copy of the first one, so it already has the ‘Airphoto’ dataset loaded.
2 Right-click on the new (lower) Green layer, then select Blue from the
shortcut menu.
The Green layer changes to a Blue layer.
3 From the Band Selection drop-down list, select B3:Blue.
The new Blue layer is now correctly set to display band 3 (blue) of the airphoto
dataset.
Tip:
When manipulating multiple layers, duplicating an existing layer with the desired
dataset and changing its type is usually faster than adding a new layer and loading
the desired dataset.
ER Mapper displays the RGB algorithm. You have now rebuilt the original
algorithm after deleting the Blue and Green layers earlier.
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Chapter 4#Viewing an image in RGB#z 3: Loading, adding and changing layers
Adjust the transforms of the Green and Blue layers
When displaying images in RGB, the red, green and blue layers of the algorithm
can be modified and adjusted independently of each other. This lets you “fine
tune” the image display as you desire.
1 Select the Green layer, then click the right-hand Edit Transform Limits
button in the process diagram
select Green layer, click Edit Transform Limits button
The Transform dialog box opens showing the histogram for the green band in the
airphoto dataset. Notice that the color bar and histogram are also green (this
corresponds to the green layer type).
2 Drag the transform line up along the left-hand side.
By doing this, you have increased the overall brightness of the green layer in the
algorithm, so the image appears more green than before.
3 Click the Create default linear transform
button.
The transform line returns to its default position and the image redisplays.
4 Click the Move to next blue layer in surface
dialog.
button on the Transform
ER Mapper automatically selects the Blue layer and displays its histogram.)
5 Drag the transform line up along the left-hand side.
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Chapter 4#Viewing an image in RGB#z 3: Loading, adding and changing layers
You increase the overall brightness of the blue layer in the algorithm, so the image
appears more blue than before. As you can see, the contrast of each color plane
(layer) can be adjusted independently. This is sometimes necessary for airphotos
that exhibit a color cast or other color changes characteristics.
Tip:
When the Transform dialog is open, you can use the
buttons to
move between the transforms for the Red, Green and Blue layers. (You can also do
this by selecting the layer in the Algorithm dialog.)
6 Click the Create default linear transform
button.
The transform line returns to its default position and the image redisplays.
7 Click Close on the Transform dialog to close it.
Change the Color Mode to see how it affects layers
1 In the Algorithm dialog, select the Surface tab.
2 From the Color Mode drop-down list, select Pseudocolor.
select Surface tab, select Pseudocolor mode
All three layers now have a cross (X) through them, indicating that they are no
longer valid with the current Color Mode. Red, Green and Blue layers are only
valid with the Color Mode named Red Green Blue.
Note: Whenever raster layers are not valid with the current Color Mode, they become
crossed out in the layer list. ER Mapper treats inactive layers as if they are turned
off when processing the algorithm.
3 Click OK on the ER Mapper error dialog.
4 From the Color Mode drop-down list, select Red Green Blue.
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Chapter 4#Viewing an image in RGB#z 4: Labelling and saving the algorithm
Note: Black and white airphotos usually have only one band of data. To display them,
you use the Color Mode named Pseudocolor, a layer of type Pseudo, and the
‘greyscale’ Color Table to create black and white image.
4: Labelling and saving the algorithm
Objectives
Learn to specify description labels, titles, and comments for an algorithm, and
save the algorithm processing steps to a file so you can view it later.
Enter a description for the entire algorithm
1 In the Algorithm dialog, select the text in the Description text field (it
currently reads ‘RGB 321’).
(To select the text, either drag through it, or triple-click to select the entire line.)
2 Type the following text, then press Enter or Return on your keyboard:
Airphoto in RGB
This text now becomes a brief description for the entire algorithm.
Save the processing steps to an algorithm file on disk
1 From the File menu (on the main menu), select Save As....
The Save Algorithm file chooser dialog opens.
2 From the Directories menu, select the path ending with the text
examples\. (The portion of the path name preceding it is specific to your
site.)
3 Double-click on the directory named ‘airphoto_training’ to open it.
4 In the Save As: text field, click to place the cursor, then type the following
name for the algorithm file:
Airphoto_in_RGB
5 Click the Apply button to save the algorithm and leave the dialog open.
Your RGB algorithm is now saved to an algorithm file on disk.
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Chapter 4#Viewing an image in RGB#z 4: Labelling and saving the algorithm
Add comments to the algorithm
1 On the Save Algorithm dialog, click the Comments... button.
2 In the comments dialog, type the following information:
This algorithm displays the airphoto as an RGB
algorithm. A 99% autoclip transform is used to increase
image contrast.
3 Click OK on the comments dialog to save your comments.
4 Click Cancel on the Save Algorithm dialog close it.
Close the image window and the Algorithm dialog
1 Close the image window:
•
For Windows, click the
Close button in the upper-right window corner.
2 On the Algorithm dialog, click the Close button.
Only the ER Mapper main menu is now open on the screen.
What you
learned...
88
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Open a dataset directly and have ER Mapper create a display algorithm
•
Use the Image Display and Mosaic Wizard to display an RGB algorithm
•
Understand the red, green and blue layers in an RGB algorithm
•
Delete, add and change layers in an algorithm
•
Use transforms to adjust the RGB color contrast
ER Mapper Workbook - Airphoto Mosaic Applications
5
Image rectification
This chapter explains how to use ER Mapper to geometrically correct raw
airphotos and rectify them to real world coordinate systems and map projections.
This is an essential step when creating a mosaic of images.
About image rectification
In order to create a mosaic of two or more airphotos, you must geometrically
correct the raw airphoto dataset to a known map coordinate system. A common
way to do this is by selecting ground control points (GCPs) between the raw
airphoto and a reference image or map, and then creating a new output image that
is rectified (or geocoded) to the real world coordinate system.
raw (uncorrected) airphoto
airphoto corrected to the UTM
coordinate system
ER Mapper Workbook - Airphoto Mosaic Applications 89
Chapter 5 Image rectification z About image rectification
A ground control point (GCP) is a point on the earth’s surface where both image
coordinates (measured in rows and columns) and map coordinates (measured in
degrees of latitude and longitude, meters, or feet) can be identified. Rectification is
the process of using GCPs to transform the geometry of an image so that each
pixel corresponds to a position in a real world coordinate system (such a UTM or
State Plane map projection). This process is sometimes called “geocoding” or
“rubbersheeting” because the image data are stretched or compressed as needed to
align with a real world map grid or coordinate system.
To perform a control point rectification, you need a raw and reference dataset:
•
The raw dataset is simply a digitized airphoto that has been imported into
ER Mapper
•
The reference dataset is any other dataset, hardcopy map, or set of known
coordinate points that can be used to correct the raw dataset. You can use another
airphoto or image that has already been rectified, a geocoded vector dataset, a
hardcopy map mounted on a digitizing table, or GPS survey points of known
features in your image (such as buildings or road intersections).
Note: Some airphoto datasets have already been rectified before import into ER Mapper.
These include orthorectified datasets such as the USGS Digital Ortho Quad (DOQ)
series and others. In this case, you do not need to rectify the dataset in ER Mapper,
you only need to make sure the proper datum, projection, and other parameters are
specified (usually using the dataset header editor).
Note: Orthorectification, which is described in the next chapter, is a more accurate
method for geocoding images. For this reason, it is generally recommended for use
with airphotos.
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Chapter 5#Image rectification#z Hands-on exercises
In this exercise, you will perform an image-to-image rectification. A typical
procedure for performing an image-to-image rectification is as follows:
Geocoding
Wizard
Open the Ortho and Geocoding Wizard, enter the
raw (uncorrected) and reference images, and start
the Define Ground Control Points function
Manually
Choose 4
GCPs
Choose the first 4 ground control points between
the raw (FROM) image window and the reference
(TO) image window
Choose
additional
GCPs
Choose additional GCPs using an automated
technique based on the transformation defined
by the first 4 GCPs
Refine or
delete GCPs
Refine the location of individual GCPs (or delete
GCPs) as needed to reduce the overall RMS error
to an acceptable threshold
Rectify the
image
Create a new output dataset rectified to the
reference dataset’s datum and map projection
Evaluate
registration
accuracy
Evaluate the accuracy of the rectification
using simple overlays or other techniques
Hands-on exercises
These exercises give you practice using ER Mapper’s Rectification features.
What you will
learn...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Choose common ground control points (GCPs) between two images
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Chapter 5 Image rectification z 1: Setting up the raw and reference images
Before you
begin...
•
Use options to modify the GCP display and edit GCPs
•
Evaluate the error associated with GCPs
•
Rectify a “raw” image to the chosen datum and projection of a reference dataset
•
Evaluate registration accuracy using a simple overlay method
•
View the map coordinates of any part of the rectified image
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
Note: It is very important to adhere to the following procedures exactly as written.
Choosing GCPs can be a fairly complex procedure, and you will learn the basic
concepts best by following these exact steps the first time. After you become
familiar with the basic procedures, you can modify them as you like.
1: Setting up the raw and reference images
Objectives
Learn how to open the Ortho and Geocoding Wizard and enter the raw and
reference images.
Open the Ortho and Geocoding Wizard
1 On the Common Functions toolbar, click on the Ortho and Geocoding
Wizard
button.
Ortho and Geocoding
Wizard
The Geocoding Wizard dialog opens with the Start tab selected.
2 On the Geocoding Wizard dialog, click the Load Algorithm or Dataset
button.
A file chooser dialog box appears.
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Chapter 5#Image rectification#z 1: Setting up the raw and reference images
Enter the file name of the raw dataset
1 From the Directories menu on file chooser dialog, select the path ending
with \examples.
2 Double-click on the directory ‘Applications’ to open it, then double-click on
the directory, ‘Airphoto’ followed by ‘1_Geocoding’.
3 In the 1+Geocoding directory, double-click on the
‘San_Diego_Airphoto_34_not_rectified.ers’ file to load it.
This is an Airphoto of downtown San Diego, which has not yet been rectified.
Note: You can also load ER Mapper algorithm files for rectification.
4 In the Geocoding Type box, select Polynomial.
This specifies that Polynomial rectification is to be used. Polynomial uses
polynomial equations to transform the raw dataset to the rectified output grid, it is
best for reducing global distortion. The other option, Triangulation, uses a mesh
of triangles between each set of three GCPs, and does a linear rectification within
each triangle (best for highly skewed data because it reduces local distortion).
Select the Polynomial Order
1 Click on the 2) Polynomial Setup tab to go to the next page of the
Geocoding Wizard.
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Chapter 5 Image rectification z 1: Setting up the raw and reference images
2 On the Polynomial Order box, select Linear.
The Polynomial Order is the geometric coordinate transformation that relocates
every pixel in the input (raw) dataset to its proper position in the output (rectified)
dataset (also called spatial interpolation). The order is the highest exponent used
in the polynomial equation, with Linear being first-order, Quadratic second-order,
and Cubic third-order. In general, you should select the lowest order that gives an
acceptable RMS. You must have at least 3 GCPs to perform a Linear rectification,
6 for Quadratic, and 10 for Cubic
Enter the file name of the reference dataset
1 Click on the 3) GCP Setup tab to go to the next Geocoding Wizard page.
2 On the GCP Picking Method box, select the Geocoded image, vectors
or algorithm option.
The Load Corrected Algorithm or Dataset
you to select the reference dataset.
button will appear to allow
You also have the option of selecting the GCPs from a paper map on a digitizer
table or typing the GCP coordinates directly in on the 4) GCP Edit wizard page.
3 Click on the Load Corrected Algorithm or Dataset
file chooser dialog box.
button to open a
4 From the Directories menu on file chooser dialog, select the path ending
with \examples.
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5 Double-click on the directory ‘Applications’ to open it, then double-click on
the directory, ‘Airphoto’ followed by ‘1_Geocoding’.
6 In the 1+Geocoding directory, double-click on the
‘San_Diego_Airphoto_34_rectified.ers’ file to load it.
This is an Airphoto of downtown San Diego, which has previously been rectified.
You should also note that the Output Coordinate Space box displays the geocoding
information of the reference dataset.
If you want the output rectified dataset to have different coordinate information,
you can click on the Change... button to open the Geocoding Wizard Output
Coordinate Space dialog box.
This allows you to select the Datum, Projection and Coordinate system type for the
image. Please refer to the ER Mapper User Guide for more information.
2: Picking the first four GCPs
Objectives
Learn how to start the Define Ground Control Points function, and pick the first
four GCPs between the RGB airphoto and vector roads image windows.
Open the GCP editor and remove existing GCPs
1 Click on the 3) GCP Setup tab to go to the next Geocoding Wizard page.
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ER Mapper opens several image windows and dialog boxes. You should see a
screen setup similar to this one:
UNCORRECTED
GCP ZOOM
WINDOW
CORRECTED GCP
ZOOM WINDOW
UNCORRECTED
GCP (OVERVIEW
ROAM geolink)
WINDOW
ER Mapper
main menu
CORRECTED GCP
(OVERVIEW ROAM
geolink) WINDOW
Geocoding Wizard
dialog box
Note: If your system does not position the windows automatically, rearrange them as
shown above before proceeding.
2 On the Geocoding Wizard dialog, click on the Delete all GCPs
to remove any GCPs that may have previously been picked.
button
Delete all GCPs
You can save all geocoding information in the header file of the raw dataset. This
means that you do not have to re-enter it when you next geocode the image. We
will use this feature in later exercises. For this exercise we will remove all
previously entered information.
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Setup the image windows to pick the first four GCPs
When you first begin picking GCPs, your “raw” (unrectified) image contains no
ground control points. You will begin by picking the first four control points using
the CORRECTED and UNCORRECTED image windows. Once you have picked
the first four GCPs, you can use the CORRECTED windows to quickly pick the
remaining GCPs.
Note: The reference image only covers a part of the raw image. This means that we can
only rectify that part of the image with any accuracy. We will crop the output
rectified image to be the same size as the reference image by setting the extents
later in this exercise.
1 On the main menu, click the Edit Algorithm
Algorithm window.
button to open the
2 Click inside the ’CORRECTED GCP ZOOM’ window to activate it.
3 In the Algorithm window, turn off the Smoothing option.
4 Click your right mouse button inside the ‘CORRECTED GCP ZOOM’
window, and select Zoom to All Datasets from the Quick Zoom menu.
The ‘CORRECTED GCP ZOOM’ window zooms out to the full image extents.
5 Click inside the ‘UNCORRECTED GCP ZOOM’ image window to activate
it.
6 In the Algorithm window, turn off the Smoothing option.
7 Click your right mouse button inside the ‘UNCORRECTED GCP ZOOM’
window, and select Zoom to All Datasets from the Quick Zoom menu.
The ‘UNCORRECTED GCP ZOOM’ window zooms out to the full image extents.
You are now ready to pick your first GCP.
8 Click Close on the Algorithm window to close it.
Note: It is a good idea to turn off the Smoothing option on algorithms where you will
pick ground control points. This makes it easier to see the locations of individual
image pixels when you zoom in closely to areas.
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Pick a GCP in the upper-left part of both images
Note: Make sure the main ER Mapper menu is not hidden by the image windows–move
it slightly if needed so you can easily access the toolbars.
1 On the main menu, click the ZoomBox Tool
toolbar button.
2 Point to the ‘UNCORRECTED GCP ZOOM’ image window, and zoom in on
a small area in the upper-left part of the image with well defined features
(drag a zoom box).
3 Move the pointer over the ‘CORRECTED GCP ZOOM’ image window
(notice the pointer is a
icon), and click once to activate the window.
4 In the ‘CORRECTED GCP ZOOM’ image window, drag a box to zoom in on
the same geographic area you have displayed in the ‘UNCORRECTED’
window.
You have now zoomed to a common area in both images to pick a GCP.
5 On the main menu, click the Pointer Tool
toolbar button.
6 In the ‘CORRECTED GCP ZOOM’ window (which is active), click on a
clearly identifiable feature in the image, such as a sharp boundary between
red vegetation and white barren land.
ER Mapper marks the control point with green cross hairs, and the geographic
location of that point appears in the Easting and Northing fields on the Geocoding
Wizard GCP Edit dialog. (This dialog has many options you will learn more
about later.)
7 Click once inside the ‘UNCORRECTED GCP ZOOM’ window to activate it.
8 Click on exactly the same geographic feature in the ‘UNCORRECTED GCP
ZOOM’ window. (It is important to be as accurate as possible).
ER Mapper marks the control point with cross hairs, and the image pixel location
of that point in the raw image appears in the Cell X and Cell Y fields on the GCP
Edit dialog. The location of each point is marked with a white “X” in each image
with the number “1.” You have now picked the first GCP.
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.
Cell X & Y location of
GCP in raw image
Eastings & Northings
of GCP in reference image
Pick a second GCP in the lower-left of both images
1 On the Geocoding Wizard GCP Edit tab, select Auto zoom.
The ZOOM windows will now automatically zoom into the point selected in the
corresponding OVERVIEW ROAM windows.
2 On the Geocoding Wizard Edit GCP dialog, click the Add new GCP
button.
3 Click on a well defined feature in the ‘UNCORRECTED GCP (OVERVIEW
ROAM geolink)’ window to select it.
The ‘UNCORRECTED GCP ZOOM’ window will zoom ito the selected point
4 Click once in the ‘CORRECTED GCP (OVERVIEW ROAM geolink)’
window to activate it, then click on the same feature to select it as a GCP.
The ‘CORRECTED GCP ZOOM’ window will zoom ito the selected point
5 Use the two ZOOM windows to adjust the positions of the GCP.
You have now picked a second GCP in the image.
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Pick two more GCPs in the upper- and lower-right
1 Following the steps from the previous section, pick a GCP near the upperright and lower-right corners of the images.
Tip:
When picking the first four GCPs, it is best to pick them in the four corners of the
CORRECTED image (if this is possible). This will make the Calculate from
point function you will use next as accurate as possible. (In this case there was
ocean in the lower-left, so you picked a point in the closest area possible.)
Once you have picked the first four GCPs, notice that ER Mapper now displays
values in the ‘RMS’ field on the GCP Edit dialog. The Root Mean Square (RMS)
error is a measurement of the accuracy of the GCP in this image expressed in the
image’s pixel size. (An RMS of 1.00 would be 80 meter positional error in the case
of the Landsat MSS data used here.) If you have done an accurate job selecting the
first four GCPs, the RMS should be one or less.
When an RMS can be calculated, ER Mapper can now use the coefficients
generated from the first four points to “predict” the location of ‘UNCORRECTED’
(raw) points when you pick additional points in the ‘CORRECTED’ (rectified)
image. This feature makes selection of the remaining points much faster and easier,
and you will use it next.
About RMS errors
GCPs are used to compute a mathematical transformation to rectify the raw image
to a geographic frame of reference (in this case, the UTM map projection of the
vector dataset). Using coordinate transform coefficients computed from the GCPs,
it is possible to model geometric distortions in the raw airphoto.
A common way to measure this distortion is by computing the root mean square
(RMS) error for each control point. This value represents the accuracy of the GCP
in the image. ER Mapper is able to compute the RMS error when you have
selected at least four control points.
The RMS error is expressed in the dataset’s pixel size (or corresponding units of a
vector dataset). This raw airphoto has a pixel size of 2 meters, so an RMS of 5.00
represents a 10 meter positional error. GCPs with lower RMS errors are more
accurate than ones with higher errors, and you should strive to pick your control
points with the lowest possible RMS error. If you have control points with high
errors, you can try to adjust them to decrease the error, or delete them. (Steps for
adjusting GCPs will be covered later.)
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3: Picking additional GCPs in the images
Objectives
Learn how to use the overview image window and “Calculate uncorrected point”
function to help speed and simplify picking of the remaining control points.
After you have picked your first four GCPs, ER Mapper can use the resulting
geometric model to predict where a point picked in the reference ‘CORRECTED’
image will be located in the raw ‘UNCORRECTED’ image. Based on this, you
will use a different technique for picking the rest of your control points for this
exercise.
Pick additional GCPs using the Corrected GCP Overview window
1 On the main menu, click the Set Pointer mode
button (if needed).
2 If needed, activate the ‘CORRECTED GCP (OVERVIEW ROAM geolink)’
window by clicking in it.
3 On the Geocoding Wizard Edit GCP dialog, click the Add GCP
button.
4 In the ‘CORRECTED GCP (OVERVIEW ROAM geolink)’ window, click on a
well defined feature near the center of the image.
ER Mapper marks the control point with cross hairs, and enters the geographic
location of GCP #5 in the TO Easting and Northing fields. The ‘CORRECTED
GCP ZOOM’ window zooms into the point for you to adjust its position.
5 In the Geocoding Wizard GCP Edit dialog, click the Calculate from point
button.
ER Mapper automatically enters values in Cell X and Cell Y fields–this is the
“predicted” location of GCP #5 in the FROM image.
Notice that the new GCP #5 has an RMS error of zero. Since it’s location is
computed from the existing points, it adds no new information to the rectification
model (and is therefore not yet a true GCP). Next you need to “fine tune” the
location of the point in the ZOOM windows to make it a true GCP.
6 Click once in one of the ZOOM windows to activate it, then click on the
GCP in the image. Adjust its position if necessary.
ER Mapper repositions GCP #5 to the new position, and calculates an RMS value
to display in the Geocoding Wizard GCP Edit dialog box.
You have now picked a fifth GCP using the “predict FROM points” technique.
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Tip:
You can keep clicking in the UNCORRECTED AND CORRECTED ZOOM
windows as many times as needed to refine the GCP location.
Pick several other points spread throughout the images
1 Using the procedure in steps 2-6 above, pick several other GCPs well
spread throughout the image (pick at least 10).
Tip:
If the default magnification level in the ZOOM windows is too great or small for
your taste, activate each window and use the Zoom In or Zoom Out options in
the Quick Zoom menu to change the zoom factor by a fixed amount in both
windows. That zoom factor is retained for subsequent points. (If you make a
mistake, you can select Previous Zoom to fix it.)
Other features on the GCP Edit dialog
The GCP Edit dialog contains a number of controls to help adjust GCPs and
visualize errors and relationships between GCPs.
undo last
include GCP lock GCP
in RMS calc from editing GCP click
height at GCP
(if available)
root mean square
(RMS) error
display
polynomial grid
display
error bars
auto zoom on
selected GCP
list GCPs in
order of RMS
values
save GCPs
with raw dataset
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Chapter 5#Image rectification#z 3: Picking additional GCPs in the images
1 In the Geocoding Wizard GCP Edit dialog, click on any GCP number under
the ‘Name’ column.
ER Mapper moves the crosshairs to highlight that point in all the ‘OVERVIEW
ROAM’ and ‘ZOOM’ windows.
2 Turn off the Auto Zoom option.
3 Click on any GCP number under the ‘Name’ column.
ER Mapper moves the crosshairs to highlight that point in the ‘OVERVIEW
ROAM’ windows, but not the ‘ZOOM’ windows.
4 Click on the Zoom to current GCP
button.
ER Mapper zooms into the selected GCP in the “ZOOM’ windows.
5 Turn on the Auto Zoom option.
View the contribution of a single GCP to the RMS errors
1 In the GCP Edit dialog, click on the number under the ‘Name’ field for a
GCP with a high RMS error value. (You can scroll the GCP list or make the
GCP Edit dialog bigger to see more points at once.)
ER Mapper highlights that GCP location in the large ‘TO’ window, and zooms to
that point on the smaller zoom windows. This is now the active GCP, so any
clicking in the image windows will relocate it.
2 Click on the text ‘On’ in the second column for the selected GCP.
The text changes to ‘Off’ and all the RMS errors are recomputed without including
that GCP. Generally you will see the RMS errors of other GCPs go down when a
GCP with a high RMS is turned off. This helps you determine how the positional
error of any GCP influences the RMS of the others. This can be important when
choosing which GCPs will be used for the final image rectification. A GCP that is
turned off is marked with a red cross in all the image windows.
3 Click on the text ‘Off’ in the second column to turn the GCP on again.
The RMS errors for all GCPs are again recomputed.
Refine the location of the high error GCP
1 Turn on the Errors option.
The magnitude and direction of the calculated positional error are shown
graphically by a line extending from the GCP in the ‘UNCORRECTED GCP
ZOOM’ window. You can use this as a guide to help adjust the position of the GCP
to make it more accurate.
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2 Turn on the x10 option (if it is not already on).
When you turn on the Errors option, an additional x10 option also appears. When
x10 is turned on, the length of the error bar line is magnified 10 times to make it
more visible. (If you have very small RMS errors you may not see the error line
without the x10 option turned on.)
The length of the line is equivalent to the RMS in pixels, so a an RMS of 5 makes
a line 5 pixels long (if the x10 option is off) or 50 pixels long if x10 is on.
3 In the ‘UNCORRECTED GCP ZOOM’ window, reposition the GCP by
clicking slightly away from the original location in the direction of the error
line.
adjust GCP location by clicking
a small amount in the direction
of the error line
The RMS error for that GCP may go down, depending on where you clicked. The
RMS errors for all other GCPs are also recomputed, and they may also go down
(although some may go up as well).
(Remember that the error line is magnified 10 times with x10 turned on, so you
should generally not adjust the GCP more than one-tenth of the line length.)
4 Click on the text ‘Undo’ in the fourth column for your active GCP.
The result of your last mouse click are reversed, so the previous values are filled
into the ‘Cell X’ and ‘Cell Y’ fields for that GCP. Clicking ‘Undo’ lets you quickly
return to the previous location if you make a mistake.
5 Click on the text ‘Redo’ in the fourth column for your active GCP.
The result of your last mouse click is again restored. ‘Undo’ and ‘Redo’ are helpful
features when refining GCPs. They always apply to the last mouse click, in either
the ‘FROM’ or ‘TO’ image windows.
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Note: Sometimes an error bar will appear to indicate that you should move a GCP to an
area where it clearly does not line up with the chosen feature in the two images.
This can be due to inaccuracies in the reference dataset or other factors, so you
should not rely on the error bar as an absolute indicator. (Use it only as a general
guideline.)
Lock a GCP so cannot be edited
1 Click on the text ‘Edit’ in the third column for any GCP.
The text changes to ‘No’ and the “X” and number marking it in the image turns
green. This effectively “locks” a GCP so it cannot be edited (that is, clicking in the
image windows do not redefine it’s position). This is useful when you have several
very good GCPs and you to lock them to avoid accidentally changing them.
2 Click on the text ‘No’ in the third column to unlock the GCP.
Enter a label for a GCP
1 Select the number text for a GCP under the ‘Name’ column, and type a
short name.
You can give GCPs text labels as well as numbers to help identify them. For
example, you might label a GCP for the intersection of the two roads.
Adjust the location or delete GCPs with high errors
1 Using the information you learned previously, try to refine the location of
your five highest error GCPs to reduce their RMS error to less than 5.00.
The basic procedure is:
•
Click on the label under the ‘Name’ column of the GCP you want to adjust–
ER Mapper selects the GCP and zooms to it in the two left-hand zoom windows.
•
Adjust the location of the GCP by clicking in the ‘UNCORRECTED GCP ZOOM’
or ‘CORRECTED GCP ZOOM’ windows to try to reduce the RMS error. (There is
a limit to how low an RMS error you can achieve, so don’t be too concerned with
this.)
•
If you cannot reduce the RMS of a particular GCP, you may choose to delete the
GCP altogether by clicking the Delete GCP
more GCPs to account for any you deleted.
button. If desired, select a few
At the end, you should have 10 GCPs with RMS errors less than 10.00, and well
distributed throughout the airphoto image.
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Chapter 5 Image rectification z 2: Perform the image rectification
Tip:
When rectifying images to create a mosaic, it is very important to try to pick GCPs
toward the edges of the image where it will overlap with other images. This will
help ensure that features on adjacent images will align well when the mosaic is
created, and minimize offset or shifted features.
View a polynomial grid over the entire airphoto image
1 On the GCP Edit dialog, turn on the Grid option.
A green polynomial grid displays over the airphoto image and the three other
image windows. This grid is a simple “preview” of the way in which the FROM
(raw) dataset pixels will be reprojected or translated onto the new coordinate grid
of the TO dataset. The geometry of the raw airphoto image will be changed during
the rectification process so that the grid would be aligned straight up and down.
Typically, the grid should appear as straight, evenly spaced lines for images that
cover small geographic areas like this one. If you were to see skewing or warping
of the grid, this indicates a poor fit of the GCPs in that area of the image.
2 Turn off the Grid option
Save the GCPs to the raw dataset
1 Click Save on the GCP Edit dialog. When asked confirm saving the GCPs
to disk, click Yes.
ER Mapper saves the GCPs to the header file of the raw airphoto dataset. These
will be used to rectify the raw dataset to the UTM map projection coordinates
obtained from the vector roads dataset.
2: Perform the image rectification
Objectives
Learn how to use the ground control points you selected to rectify the image to
the selected datum and map projection.
Specify output (rectified) image file
1 Select the Geocoding Wizard Rectify tab.
2 Click the file chooser
button in the Output Info box.
3 From the Directories menu, select the path ending with \examples.
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4 Double-click on the ‘airphoto_training’ directory to open it.
5 Enter the filename San_Diego_rectified_polynomial (start with
your initials), then click OK.
6 In the Resampling: in the Cell Attributes box select ‘Nearest Neighbour’.
The Cell Attributes box also lets you resample the output image to a different cell
size (Output Cell width and height), and specify a null cell value.
Set extents of output image
The reference dataset covers a smaller area than the raw dataset. We can edit the
extents of the output rectified image so that it covers the same area as the reference
dataset.
1 On the Geocoding Wizard dialog, click on the Edit Extents button to open
the Geocode Output Extents dialog box.
This box allows you to specify the extents of the output rectified image. For
Polynomial rectification you can set this in three ways:
Maximum extents
This is the default setting, which sets the extents to be
that of the full raw image.
Custom extents
Allows you to enter the exact top left and bottom right
coordinates of the image. We will be using this option.
Snapshot.
This is enabled when the Custom extents option is
chosen. It automatically enters the coordinates of the
zoomed in the currently active window.
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2 Select the Custom extents option and enter the Easting/Northing values
shown below.
These values are the coordinate extents for the reference image. Note that the
Latitude and Longitude values change automatically as you change the Eastings
and Northings values.
3 Click on the OK button to exit the Geocode Output Extents dialog box.
Create the output rectified image on disk
1 Check that the Output Info and Cell Attributes are similar to what is shown
below:
Size of rectified
image file.
Physical size of
rectified image
2 If the values are not similar to what is shown above, Click on the Default
Cell Size button.
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Leave the Null cell value box unchecked, so that the rectified image will use the
same null cell value (if any) as that of the reference image. If you check the box,
you can enter a null cell value.
3 Select Display rectified image to display the image after it is rectified.
4 Click on the Save file and start rectification button.
ER Mapper opens a status dialog to indicate the progress of the rectification. This
should take about five minutes to complete.
5 When the operation finishes, click OK on the successful completion dialog.
6 Click on the Close button to exit the Geocoding Wizard.
You have now rectified the uncorrected San Diego airphoto correspond to the 1927
North American Datum (NAD27) and UTM zone 11 (NUTM11) map projection.
3: Evaluating image registration
Objectives
Learn a simple way to visually evaluate the registration of two images using an
overlay technique. In this case, you will evaluate the registration of the raw image
you rectified and the rectified MSS image supplied with ER Mapper.
Evaluate the image orthorectification
1 On the main menu, click the Edit Algorithm
Algorithm window.
button to open the
2 The Algorithm window shows the Red, Green and Blue layers of the
orthorectified image ‘<your Initials>_Airphoto_orthorectified’
3 In the Algorithm window, click on the Blue layer to select it.
4 Click the Load Dataset
button in the algorithm process diagram.
5 From the Directories menu, select the path ending with \examples.
6 Double-click on the ‘Applications’ directory to open it.
7 Double-click on the ‘Airphoto’ and then on ‘1_Geocoding’ directory to open
it.
8 Click once on the image ‘San_Diego_Airphoto_34 _rectified.ers’ to select
it, then click OK this layer only button to load it into the Blue layer. (The
Red and Green layers should still have the your rectified image.)
9 Select B3:Blue from the Blue layer’s Band Selection drop-down list.
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Chapter 5 Image rectification z 3: Evaluating image registration
Display the two images to evaluate registration
1 Click the 99% Contrast Enhancement
toolbar button.
This image combines two different images–one in the Red and Green layers and
one in the Blue layer. If your images are well aligned the image appears normal. If
you see areas that are dominantly yellow or blue, this indicates poor registration.
2 On the Algorithm window, turn off the Smoothing option.
3 On the main menu, click the ZoomBox tool toolbar button.
4 Drag a zoom box over a very small area of the image that contains land
and water.
Errors in registration appear as either blue or yellow pixels because this is where
the two images do not align perfectly. This is a very simple way to evaluate the
registration of two images. If the RMS errors of your GCPs were generally less
than one, you should not see more that one pixel offsets or registration errors.
Blue and yellow pixels
indicate areas of poor
registration
View geographic coordinates in the image
1 On the main menu, click the Pointer Tool
button.
You must use the Pointer tool to view geographic coordinates in an image.
2 In the Algorithm dialog, select the ‘Blue Layer’ in the layer list.
3 From the View menu, select Cell Coordinate....
The Cell Coordinates dialog appears. Drag it next to the image window.
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The upper three fields of this dialog show the location of the current pixel in
dataset column (X) and row (Y) coordinates, and the Eastings/Northings and
Latitude/Longitude coordinate systems.
4 Point to the image window, and drag the pointer through the image.
The dataset and geographic location of the current cell appear, and are updated as
you drag the mouse. Using this, you can query the geographic location of any
feature in your rectified airphoto.
column (X) and row (Y)
location of cursor
geographic location
of cursor in image
Note: The Easting Northing and Latitude Longitude field values only display if the
dataset is rectified to a map projection. If you are displaying a “raw” image, only
values dataset X and Y pixel locations are displayed.
View distances between points in the image
The lower three fields of the Cell Coordinate dialog show distance between the
point where you first depress the mouse button and the point where you release it.
Distances are shown as Imperial distance (feet and miles), Metric distance (meters
and kilometers), and Dataset distance (number of pixels in the X and Y directions).
1 Point to the image window, and click on any point in the image.
The Imperial, Metric, and Dataset distance fields are cleared to zero values.
2 Pick out two features in the image, then drag the mouse between them.
This distance between those two points is displayed when you release the mouse
button. Measuring the distance between two points is called mensuration.
distance between
points in image
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3 Click the Close button on the Cell Coordinates dialog box to close it.Close
all image windows and dialog boxes
4 Close all image windows using the window system controls:
•
For Windows, select Close from the window control-menu.
5 Click Close on the Algorithm window to close it.
Only the ER Mapper main menu should be open on the screen.
Only the main menu should be open on the screen.
What you
learned...
112
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Choose common ground control points (GCPs) between two images
•
Use options to modify the GCP display and edit GCPs
•
Evaluate the error associated with GCPs
•
Rectify a “raw” image to the chosen datum and projection of a reference dataset
•
Evaluate registration accuracy using a simple overlay method
•
View the map coordinates of any part of the rectified image
ER Mapper Workbook - Airphoto Mosaic Applications
6
Image
orthorectification
This chapter explains how to use the ER Mapper Geocoding Wizard to
geometrically correct raw image data and orthorectify it to real world coordinate
systems and map projections.
About orthorectification
Orthorectification is more accurate than Linear or Polynomial rectification because
it corrects local and global distortions in an image by adjusting for camera
characteristics, platform positions and terrain details.
The camera characteristics, derived from a camera calibration report, are stored in
a camera file for use by the Geocoding Wizard.
The terrain details are supplied in the form of a DEM. If the terrain is relatively
flat, you can use an average height value.
In the case of Advanced Orthorectification, the platform position is determined by
exterior orientation values which describe the exact position of the aircraft at the
time the image was taken, and how this relates to the image. The following
parameters are specified:
Attitude omega
The tilt angle (roll) of the aircraft; i.e. the rotation about
the X axis (direction of travel).
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Chapter 6 Image orthorectification ● About orthorectification
Attitude phi
The swing angle (pitch) of the aircraft; i.e the rotation
about the Y axis.
Attitude kappa
The azimuth angle (yaw)of the aircraft; i.e the rotation
about the Z axis.
Exposure center XYZ
The co-ordinates of the exposure center of the image.
If the exterior orientation parameters are not known, you have to specify about 4 to
6 GCPs for the Geocoding Wizard to compute them.
To use Orthorectification you must have the following information available:
•
Camera file containing camera calibration information
•
DEM file (You can enter an average height if the terrain is relatively flat)
•
Exterior orientation (Only for Advanced Orthorectification. Otherwise you must
select GCPs)
•
GCPs referenced by their XYZ coordinates.
The diagram below illustrates the required inputs for orthorectification.
Camera
Calibration
Report
Camera
Wizard
Exterior Orientation
DEM
Camera File
OR average
height
Roll
Pitch
Yaw
Exposure
Center
Ground
OR Control
Points
Uncorrected
image (airphoto)
Corrected
image (airphoto)
Geocoding Wizard Orthorectification
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Chapter 6 Image orthorectification ● Hands-on exercises
Hands-on exercises
These exercises give you practice using ER Mapper’s Geocoding Wizard to
orthorectify an airphoto image.
What you will
learn...
Before you
begin...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Use the Geocoding Wizard to orthorectify an airphoto
•
Use the Camera Wizard to create a Camera File from a calibration report
•
Locate fiducial marks on an airphoto
•
Pick suitable Ground Control Points (GCPs)
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
In these exercises you will use the Geocoding Wizard to orthorectify the same
airphoto image of San Diego taken in 1997, that we used in the previous chapter.
we will then be able to compare the results. The example images are used with
permission from Aerial Fotobank.
1: Orthorectify an airphoto using GCPs
Objectives
Learn how to use ER Mapper’s Geocoding Wizard to orthorectify an airphoto.
Use the Camera Wizard to create a Camera File with given calibration
parameters.
Select Ground Control Points
Open the Geocoding Wizard
1 Click on the Ortho and Geocoding Wizard
Functions toolbar.
button in the Common
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
The Geocoding Wizard will open with the 1) Start tab selected.
2 Click the Load Algorithm or Dataset
open the file chooser.
button in the Input file: field to
3 From the Directories menu, select the path ending with the text
\examples.
4 Select the directory ‘Applications\,Airphoto\1_Geocoding’ and then doubleclick on ‘San_Diego_Airphoto_34_not_rectified.ers’ to select it.
5 Select the Geocoding Wizard Orthorectify using ground control points
option.
In this example, you do not have exterior orientation parameters which provide
information on the position of the platform or aircraft. Instead, you will pick GCPs
so that the wizard can compute the exterior orientation parameters. If these
parameters were available, you would have chosen the Orthorectify using
exterior orientation option.
6 Select the 2) Ortho Setup tab.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
Enter terrain and camera details
This tab allows you to enter the terrain details in the form of a DEM or as an
average height value. Obviously, using a DEM would produce a more accurate
result. However, if the terrain is relatively flat, you can enter an average value. In
this example you will enter the name of a DEM file.
You supply the camera details to the Geocoding Wizard in the form of a camera
file. If the applicable camera file does not exist, you can use the Camera Wizard to
create one.
1 Select the Use a DEM file as height option in the DEM Setup box.
Notice that the DEM Setup box changes according to the option that you choose.
Because you selected the Use a DEM file as height option, the DEM Setup box
displays a file and a band chooser for you to select the DEM file and the required
data band.
2 Click on the Load input DEM File
button to open the file chooser.
3 Select the file ‘San_Diego_DEM.ers’ from the
‘examples\Applications\,Airphoto\1_Geocoding’ directory and click on the
OK button to return to the Geocoding Wizard.
4 Click on the Camera Wizard
dialog.
button to open the Camera Wizard
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
Create a Camera file
The Camera Wizard creates a Camera file for the Geocoding Wizard to use. It does
this by providing a number of dialog boxes for you to enter camera calibration
information. You normally get this information from a camera calibration report. If
you do not have a valid calibration report for the camera that was used to take the
image, you can use a generic report for that camera model. This could result in a
some inaccuracies.
1 Click on the Create new option to create a new Camera File.
You could edit an existing Camera File, in which case the wizard provides you
with the Camera file: field and chooser to enter the name of the existing file.
2 Click on the Next> button to go to the Camera identification page.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
The information you enter here is not used by the Geocoding Wizard. Therefore it
can be omitted. It is, however, a good idea to include it because it is a means of
identifying the camera and the calibration report in the future.
3 Enter the following information in the applicable fields:
Manufacturer:
Wild
Model:
RC20
Lens serial number:
13115
Date calibrated:
Day: 31 Month:10 Year: 1998
4 Click on the Next> button to go to the ‘Camera attributes page’.
Use this page to enter information on the focal length of the camera lens. The
Camera Wizard uses this information, so it must be entered. In addition, you can
enter information on the position of the Principal Point relative to the lens center as
a measure of lens distortion. Any distortion in the lens would cause the principal
point to be offset from the lens center.
5 Enter the following information in the applicable fields:
Focal length:
152.793
X offset to principal point: 0
Y offset to principal point: 0
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
This is the ideal case where the principal point is at the lens center on the focal
plane. Lens distortion could cause it to be slightly off-center, and this is
represented by the X and Y offsets to the principal point. The diagram below
illustrates this by exaggerating the lens distortion.
Principal
point
Lens
X offset
Focal length
Y offset
Lens center
Focal
plane
6 Click on the Next> button to go to the ‘Number of Fiducial points’ page
Aerial photography cameras insert Fiducial marks around the edges of the airphoto
images. The Geocoding Wizard uses the positions of these marks to relate the
image to the camera model. Different cameras insert these marks in different
places on the image. Use this page to specify where the camera has placed the
Fiducial marks. If you specify four Fiducial marks where the camera has, in fact,
inserted eight, the Geocoding Wizard will only take into consideration the four you
specified.
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7 Select the All 8 option; indicating that the Fiducial points are on the four
corners and the middle of edges of the image.
8 Click on the Next> button to got to the ‘Fiducial point offsets’ page.
This page enables you to specify the positions of the fiducial points relative to the
principal point.
9 Enter the following values in the applicable fields:
Top left
X:-105.99 Y:106.01
Middle top
X: 0.011 Y: 110.01
Top right
X:106.01 Y:106.02
Middle left
X:-109.99 Y: 0.012
Middle right
X:110.01 Y: 0.013
Bottom left
X:-105.99 Y:-105.99
Middle bottom
X:-0.005 Y: -109.99
Bottom right
X:106.0l Y:-105.99
Note: The data strip is not always on the left side of the image. Ensure that your scanned
image has the data strip on the same side as what is specified in the Camera File. If
not, you will have to either change the Camera file or rotate the scanned image.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
10 Click on the Next> button to go to the ‘Finish’ page.
11 Click the Save
button in the Camera file: field to open the file chooser
to select a directory and file name to which to save the new camera file.
12 From the Directories menu, select the path ending with the text
\examples.
13 Select the directory ‘airphoto_training’, and then enter ‘camera_<your
initials>’ in the Save as: field.
14 Click on the OK button to return to the Camera Wizard.
The file name and directory you entered should now be displayed in the Camera
file: field.
15 Click on the Finish button to return to the Geocoding Wizard.
16 Click the Load Camera File
button in the Geocoding Wizard Camera
file: field to open the file chooser.
17 From the Directories menu, select the path ending with the text
\examples.
18 Select the directory ‘airphoto_training’, and then double-click on the
‘camera_<your initials>’ file you saved.
19 Click on the 3) Fiducial Point Edit tab.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
Edit the fiducial points
This wizard page enables you to enter the locations of the fiducial points on the
image into ER Mapper.
ER mapper opens two image windows one in OVERVIEW ROAM mode, and the
other in ZOOM mode.
ZOOM
OVERVIEW ROAM
1 Select the Auto zoom option. This causes the ZOOM window to
automatically zoom to the selected fiducial mark.
2 Select the Pointer Tool
on the Standard toolbar.
3 On the table, select ‘Top Left’ in the ‘Name’ column.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
4 In the OVERVIEW ROAM window, click on the Fiducial mark on the top left
corner of the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
5 On the table, select ‘Top Right’ in the ‘Name’ column.
6 In the OVERVIEW ROAM window, click on the Fiducial mark on the top
right corner of the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
7 On the table, select ‘Bottom Left’ in the ‘Name’ column.
8 In the OVERVIEW ROAM window, click on the Fiducial mark on the bottom
left corner of the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
9 On the table, select ‘Bottom Right’ in the ‘Name’ column.
10 In the OVERVIEW ROAM window, click on the Fiducial mark on the bottom
right corner of the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
11 On the table, select ‘Middle Left’ in the ‘Name’ column.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
12 In the OVERVIEW ROAM window, click on the Fiducial mark on the middle
of the left side of the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
13 On the table, select ‘Middle Right’ in the ‘Name’ column.
14 In the OVERVIEW ROAM window, click on the Fiducial mark on the middle
of the right side of the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
15 On the table, select ‘Middle Top’ in the ‘Name’ column.
16 In the OVERVIEW ROAM window, click on the Fiducial mark on the middle
of the top the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
17 On the table, select ‘Middle Bottom’ in the ‘Name’ column.
18 In the OVERVIEW ROAM window, click on the Fiducial mark on the middle
of the bottom of the image.
The image in the ZOOM window will automatically zoom to the selected fiducial
mark. Use this to adjust the position of the cursor to the center of the red circle.
After selecting the fiducial markers, the table on the Fiducial Point Edit tab
should be similar to what is shown below.
The RMS column should show values of less than 1.00.
The image window should now have all the fiducial points labelled.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
19 If necessary, select the Errors option, and adjust the position of the
selections in the direction of the indicated errors.
The x10 option enlarges the error markers for a more accurate indication.
20 Click on the 4) GCP Setup tab.
Setup Ground Control Points
The GCP Setup tab lets you specify the way that you want to choose control
points. Control points may be entered manually, chosen from a reference image,
chosen from a digitizing tablet, or chosen using a combination of these three
methods.
In this exercise, you will use a previously orthorectified reference image to locate
GCPs.
1 In the GCP Picking Method box, select Geocoded image, vectors or
algorithm option.
This tells ER Mapper you plan to pick corresponding points between two images
on the screen.
2 Click the Load Corrected Algorithm or Dataset
file chooser button.
3 Choose ‘ER Mapper Raster Dataset (.ers)’ in the Files of Type: field.
4 From the Directories menu on the file chooser dialog, select the path
ending with the text \examples.
5 Double_click on the ‘Applications’ directory to open it.
6 Double-click on the ‘Airphoto\1_Geocoding’ directory to open it, then
double-click on ‘San_Diego_Airphoto_34_rectified.ers’ to load it.
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This is the already rectified image containing coordinate information.
Setup parameters for the image rectification
The To geodetic datum, To geodetic projection and To Coordinates,
fields in the Output Coordinate Space box show the datum, projection and
coordinate type for the output rectified file you will create. These parameters are
included automatically from the ‘CORRECTED’ (rectified) airphoto image.
7 Click on the Change... button to open the Geocoding Wizard Output
Coordinate Space dialog.
8 If necessary, change the settings to what is displayed above.
9 Click OK on the Geocoding Wizard Output Coordinate Space dialog to
close it.
10 Select the Geocoding Wizard 5) GCP Edit tab.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
Edit Ground Control Points
ER Mapper opens several image windows and dialog boxes. You should see a
screen setup similar to this one:
UNCORRECTED
GCP ZOOM
WINDOW
CORRECTED GCP
ZOOM WINDOW
UNCORRECTED
GCP (OVERVIEW
ROAM geolink)
WINDOW
CORRECTED GCP
(OVERVIEW ROAM
geolink) WINDOW
Geocoding Wizard
dialog box
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ER Mapper
main menu
Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
Note: If your system does not position the windows automatically, rearrange them as
shown above before proceeding.
The GCP Edit box should already have the GCPs you picked in the previous
exercise. To save time we can use these existing GCPs and go straight to “Rectify
the image” on page 131. Orthorectification only requires 4 to 6 GCPs, so you
might want to delete those that show a high RMS error value.
Pick a GCP in the upper-left part of both images
Note: Make sure the main ER Mapper menu is not hidden by the image windows–move
it slightly if needed so you can easily access the toolbars.
1 On the Geocoding Wizard GCP Edit tab, select Auto zoom.
The ZOOM windows will now automatically zoom into the point selected in the
corresponding OVERVIEW ROAM windows.
2 Click on a well defined feature in the ‘UNCORRECTED GCP (OVERVIEW
ROAM geolink)’ window to select it.
The ‘UNCORRECTED GCP ZOOM’ window will zoom ito the selected point
3 Click once in the ‘CORRECTED GCP (OVERVIEW ROAM geolink)’
window to activate it, then click on the same feature to select it as a GCP.
The ‘CORRECTED GCP ZOOM’ window will zoom ito the selected point
4 Use the two ZOOM windows to adjust the positions of the GCP.
You have now picked a GCP in the image.
Pick a second GCP in the lower-left of both images
5 On the Geocoding Wizard Edit GCP dialog, click the Add new GCP
button.
6 Click on a well defined feature in the ‘UNCORRECTED GCP (OVERVIEW
ROAM geolink)’ window to select it.
The ‘UNCORRECTED GCP ZOOM’ window will zoom into the selected point
7 Click once in the ‘CORRECTED GCP (OVERVIEW ROAM geolink)’
window to activate it, then click on the same feature to select it as a GCP.
The ‘CORRECTED GCP ZOOM’ window will zoom ito the selected point
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
8 Use the two ZOOM windows to adjust the positions of the GCP.
You have now picked a second GCP in the image.
9 Following the above steps, pick another four GCPs near the upper-right,
lower-right and middle of the images.
The more GCPs you pick the lower the possibility of errors. For orthorectification
you need at least six.
Try some other features on the Geocoding Wizard GCP Edit dialog
1 In the Geocoding Wizard GCP Edit dialog, click on any GCP number under
the ‘Name’ column.
ER Mapper moves the crosshairs to highlight that point in all the ‘OVERVIEW
ROAM’ and ‘ZOOM’ windows.
2 Turn off the Auto Zoom option at the bottom.
3 Click on any GCP number under the ‘Name’ column.
ER Mapper moves the crosshairs to highlight that point in the ‘OVERVIEW
ROAM’ windows, but not the ‘ZOOM’ windows.
4 Click on the Zoom to current GCP
button.
ER Mapper zooms into the selected GCP in the “ZOOM’ windows.
5 Select the number text for a GCP under the ‘Name’ column, and type a
short name.
You can give GCPs text labels as well as numbers to help identify them.
6 Click on the text ‘On’ in the second column for any GCP.
The text changes to ‘Off’ and all the RMS errors are recomputed without including
that GCP. (This is an easy way to see how the positional error of any GCP
influences the RMS of the others. For example, turning off a GCP with a large
RMS often reduces the RMS of the others.) This can be important when choosing
which GCPs will be used for the final image rectification.
7 Turn off other GCPs to see the effect, but turn all on again when finished.
8 Click on the text ‘Edit’ in the third column for any GCP.
The text changes to ‘No’ and the “X” and number marking it in the image turns
green. This effectively “locks” a GCP so it cannot be edited (that is, clicking in the
image windows do not redefine it’s position). This is useful when you have several
very good GCPs and you to lock them to avoid accidentally changing them.
9 Turn on the Errors option.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
The magnitude and direction of the calculated positional error are shown
graphically by a line for each GCP on the image. (If you have very small RMS
errors you may not see the error line, even if you increase the line length by a
factor of 10 using the x10 option.)
10 Turn on the Grid option.
A polynomial grid displays over all three image windows. This grid is a simple
“preview” of the way in which the FROM (raw) image pixels will be reprojected
onto the new coordinate grid of the TO image. (This grid is only an approximation,
in reality the lines would be curved.)
11 Click the Add new GCP
button and select a point on the
CORRECTED image.
12 Click on the Calculate uncorrected point
button. The wizard will
automatically position the corresponding GCP on the UNCORRECTED
image. Use the ZOOM windows to adjust the GCP position.
This facility is available once you have positioned four points.
13 Click Save on the Geocoding Wizard dialog. When asked confirm saving
the GCPs to disk, click Yes.
This will save the geocoding information into the header file of the
UNCORRECTED image.
14 Select the Geocoding Wizard 6) Rectify tab.
Rectify the image
1 Click the file chooser
button in the Output Info box.
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Chapter 6 Image orthorectification ● 1: Orthorectify an airphoto using GCPs
2 From the Directories menu, select the path ending with \examples.
3 Double-click on the ‘airphoto_training’ directory to open it.
4 Enter the filename ‘San_Diego_orthorectified’ (start with your
initials), then click OK.
5 Click on the Edit Extents... button to open the Geocode Output Extents
dialog box.
This dialog allows you to specify how much of the orthorectified image you want
to save. You have three main options:
Maximum extents:
Saves the whole image including any portion not visible
in the currently active image window.
Optimum extents:
Automatically calculates the extents of airphotos to
exclude the black edges around them.
Custom extents:
Allows you to specify the top left and bottom right
coordinates of the area to be included. If you click on
the Snapshot button ER Mapper will automatically
select the extents of the visible part of the image in the
currently active image window.
The Custom extents should still have the coordinates entered in the previous
exercise. This limits the extents to those of the reference image
6 Click on the OK button to return to the Geocoding Wizard.
7 In the Resampling: in the Cell Attributes box select ‘Nearest Neighbour’.
The Cell Attributes box also lets you resample the output image to a different cell
size (Output Cell width and height), and specify a null cell value.
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8 Click on the Save button to save the orthorectification parameters in the
‘San_Diego_Airphoto_34 _not_rectified.ers’ header file.
You will use this in the next exercise.
9 Select Display rectified image to display the image after it is rectified.
10 Click on the Save file and start rectification button.
ER Mapper opens a status dialog to indicate the progress of the rectification. This
should take approximately 10 minutes.
11 When the operation finishes, click OK of the successful completion dialog.
12 Click on the Close button to exit the Geocoding Wizard.
You have now rectified the uncorrected airphoto image to correspond to the 1927
North American Datum (NAD27) and UTM zone 11 (NUTM11) map projection.
13 Do not close the image window with the orthorectified image
Evaluate the image orthorectification
1 On the main menu, click the Edit Algorithm
Algorithm window.
button to open the
2 The Algorithm window shows the Red, Green and Blue layers of the
orthorectified image.
3 In the Algorithm window, click on the Blue layer to select it.
4 Click the Load Dataset
button in the algorithm process diagram.
5 From the Directories menu, select the path ending with \examples.
6 Double-click on the ‘Applications’ directory to open it.
7 Double-click on the ‘Airphoto’ and then on ‘1_Geocoding’ directory to open
it.
8 Click once on the image ‘San_Diego_Airphoto_34 _rectified.ers’ to select
it, then click OK this layer only button to load it into the Blue layer. (The
Red and Green layers should still have the ‘<your
Initials>_Airphoto_orthorectified’ image.)
9 Select B3:Blue from the Blue layer’s Band Selection drop-down list.
Display the two images to evaluate registration
1 Click the 99% Contrast Enhancement
toolbar button.
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Chapter 6 Image orthorectification ● 2: Orthorectify an airphoto using Exterior
This image combines two different images–one in the Red and Green layers and
one in the Blue layer. If your images are well aligned the image appears normal. If
you see areas that are dominantly yellow or blue, this indicates poor registration.
2 On the Algorithm window, turn off the Smoothing option.
3 On the main menu, click the ZoomBox tool toolbar button.
4 Drag a zoom box over a very small area of the image that contains land
and water.
Errors in registration appear as either blue or yellow pixels because this is where
the two images do not align perfectly. This is a very simple way to evaluate the
registration of two images. If the RMS errors of your GCPs were generally less
than one, you should not see more that one pixel offsets or registration errors.
Close all windows
1 Close all image windows using the window system controls:
•
For Windows, select Close from the window control-menu.
2 Click Close on the Algorithm window to close it.
2: Orthorectify an airphoto using Exterior
Orientation
Objectives
Learn how to use ER Mapper’s Geocoding Wizard to orthorectify an airphoto
using Exterior Orientation parameters
In this exercise you will orthorectify the same image as in the previous exercise.
This time, instead of using Ground Control Points, you will enter Exterior
Orientation parameters which have been obtained from a photogrammetry, aerial
triangulation or geoposition system external to ER Mapper. In the previous
exercise you saved orthorectification parameters in the
‘San_Diego_Airphoto_34_not_rectified.ers’ file. This means that you will not
have to re-enter them in this exercise.
Open the Geocoding Wizard
1 Click on the Ortho and Geocoding Wizard
Functions toolbar.
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button in the Common
Chapter 6 Image orthorectification ● 2: Orthorectify an airphoto using Exterior
The Geocoding Wizard will open with the 1) Start tab selected.
2 Click the Load Algorithm or Dataset
open the file chooser.
button in the Input file: field to
3 From the Directories menu, select the path ending with the text
\examples.
4 Select the directory ‘Applications\,Airphoto\1_Geocoding’ and then doubleclick on ‘San_Diego_Airphoto_34_not_rectified.ers’ to select it.
This is the same file as that you used in the previous exercise.
5 Select the Geocoding Wizard Orthorectify using exterior orientation
option.
In this example, you enter exterior orientation parameters which provide
information on the position of the platform or aircraft.
6 Select the 2) Ortho Setup tab.
The fields in the Ortho Setup page should contain the information that you entered
in the previous exercise because it was saved to the header file of the image being
orthorectified.
7 Click on the 3) Fiducial Point Edit tab.
The fields in the Fiducial Point Edit page should also contain the information you
entered in the previous exercise.
8 Click on the 4) Exterior Orientation Setup tab.
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Chapter 6 Image orthorectification ● 2: Orthorectify an airphoto using Exterior
Enter Exterior Orientation parameters
Exterior Orientation parameters contain information on the position of the
platform or aircraft at the time the image was taken. You would have to obtain this
data from a system external to ER Mapper.
If these parameters are not available then you would use Ground Control Points as
in the previous exercise.
1 Enter the information in the relevant fields as shown in the table below:
136
Field name
Description
Enter value
Attitude omega
The tilt angle (roll) of the
aircraft; i.e. the rotation
about the X axis (direction of
travel).
0.024233136466399
Attitude phi
The swing angle (pitch) of
the aircraft; i.e the rotation
about the Y axis.
0.028555797949162
Attitude kappa
The azimuth angle (yaw)of
the aircraft; i.e the rotation
about the Z axis.
0.0019776681959326
Exposure center X
The X co-ordinate of the
483681.44788264
exposure center of the image.
Exposure center Y
The Y co-ordinate of the
3621463.0778646
exposure center of the image.
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Chapter 6 Image orthorectification ● 2: Orthorectify an airphoto using Exterior
Field name
Description
Enter value
Exposure center Z
The Z co-ordinate of the
3182.9321414632
exposure center of the image.
Scale
The scale of the image
expressed as a decimal value.
0.000048745007960398
The following diagram illustrates the relationship between the parameters.
Z
Y
Exposure
center
Omega
X
Phi
Kappa
2 Click on the Change... button to open the Geocoding Wizard Output
Coordinate Space dialog.
3 Enter the Datum, Projection and Coord system type as shown below
Tip:
NUTM11 is a utm projection type.
4 Click on the 5) Rectify tab.
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Chapter 6 Image orthorectification ● 2: Orthorectify an airphoto using Exterior
Rectify the image
1 Click the file chooser
button in the Output Info box.
2 From the Directories menu, select the path ending with \examples.
3 Double-click on the ‘airphoto_training’ directory to open it.
4 Enter the filename ‘San_Diego_orthorectified_advanced’ (start
with your initials), then click OK.
5 Click on the OK button to return to the Geocoding Wizard.
6 In the Resampling: in the Cell Attributes box select ‘Nearest Neighbour’.
The Cell Attributes box also lets you resample the output image to a different cell
size (Output Cell width and height), and specify a null cell value.
7 Click on the Save button to save the orthorectification parameters in the
‘San_Diego_Airphoto_34 _not_rectified.ers’ header file.
8 Select Display rectified image to display the image after it is rectified.
9 Click on the Save file and start rectification button.
ER Mapper opens a status dialog to indicate the progress of the rectification.
10 When the operation finishes, click OK on the successful completion dialog.
11 Click on the Close button to exit the Geocoding Wizard.
You have now rectified the uncorrected airphoto image to correspond to the 1927
North American Datum (NAD27) and UTM zone 11 (NUTM11) map projection.
12 Do not close the image window with the orthorectified image
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Evaluate the image orthorectification
1 On the main menu, click the Edit Algorithm
Algorithm window.
button to open the
2 The Algorithm window shows the Red, Green and Blue layers of the
orthorectified image.
3 In the Algorithm window, click on the Blue layer to select it.
4 Click the Load Dataset
button in the algorithm process diagram.
5 From the Directories menu, select the path ending with \examples.
6 Double-click on the ‘Applications’ directory to open it.
7 Double-click on the ‘Airphoto’ and then on ‘1_Geocoding’ directory to open
it.
8 Click once on the image ‘San_Diego_Airphoto_34 _rectified.ers’ to select
it, then click OK this layer only button to load it into the Blue layer. (The
Red and Green layers should still have the ‘<your
Initials>_Airphoto_orthorectified_advanced’ image.)
9 Select B3:Blue from the Blue layer’s Band Selection drop-down list.
Display the two images to evaluate registration
1 Click the 99% Contrast Enhancement
toolbar button.
This image combines two different images–one in the Red and Green layers and
one in the Blue layer. If your images are well aligned the image appears normal. If
you see areas that are dominantly yellow or blue, this indicates poor registration.
2 On the Algorithm window, turn off the Smoothing option.
3 On the main menu, click the ZoomBox tool toolbar button.
4 Drag a zoom box over a very small area of the image that contains land
and water.
Errors in registration appear as either blue or yellow pixels because this is where
the two images do not align perfectly. This is a very simple way to evaluate the
registration of two images. If the RMS errors of your GCPs were generally less
than one, you should not see more that one pixel offsets or registration errors.
Close all windows
1 Close all image windows using the window system controls:
•
For Windows, select Close from the window control-menu.
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•
For Unix systems, press right mouse button on the window title bar, and select
Close or Quit (for systems with both options, select Quit).
2 Click Close on the Algorithm window to close it.
Only the ER Mapper main menu should be open on the screen.
What you
learned...
140
After completing these exercises, you know how to perform the following tasks in
ER Mapper:
•
Use the Camera Wizard to create a Camera File
•
Select fiducial markers on an airphoto image
•
Use options to modify the GCP display and edit GCPs
•
Enter Exterior Orientation parameters for advanced orthorectification.
•
Use the Geocoding Wizard to orthorectify a “raw” airphoto image to the chosen
datum and map projection.
ER Mapper Workbook - Land Information
7
Assembling image
mosaics
This chapter explains how to create algorithms to display and process two or more
separate airphoto images as a mosaic. You will learn how ER Mapper approaches
the concept of creating mosaics and how to build an image mosaic algorithm.
About assembling mosaics
The term “mosaic” refers to assembling two or more overlapping images to create
a continuous representation of the area covered by the images (a mosaic). In this
example, you will create a mosaic of several overlapping aerial photos to cover a
larger geographic area. The process of creating image mosaics is very simple in
ER Mapper once the images are rectified to the same datum and map projection.
Any number of co-registered images used in the same processing algorithm are
automatically displayed in their correct geographic positions relative to each other.
Requirements for mosaics
In order for ER Mapper to create a mosaic, each of the images must have the
following in common:
•
they must be registered to the same geographic datum
•
they must be registered to the same map projection
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•
they must be rotated the same amount from north (if rotation is used).
You will learn how to rectify images to datums and map projections later.
Mosaic capabilities
Other than having a common datum and map projection, you can create mosaics
that contain very different types of data. An image mosaic can be built with
datasets that have:
•
different numbers of bands (i.e., three for a color airphoto versus seven for a
Landsat satellite image)
•
different data formats (i.e., byte format versus floating point format)
•
different resolutions or cell sizes (i.e., 1-meter versus 3-meter).
Dataset display priority
By changing the order of the algorithm layers containing the separate datasets, you
can control dataset display priority (that is, which images appear on top of others
in the event of overlap). Datasets loaded into the uppermost layer of any type
always appear on top of any other datasets in layers below where overlap occurs
between them.
Datasets loaded into the lowest layer of any type always have the lowest display
priority and will only be visible in areas where there is no overlap from datasets in
layers above them. For example, if you are creating a mosaic with a high
resolution dataset and a lower resolution dataset, you can display the entire extents
of the high resolution dataset by putting its layer(s) on top in the algorithm layer
list.
Note: Layer priority only applies to raster layers; vector layers always appear on top of
raster layers regardless of their position in the algorithm layer list.
Hands-on exercises
These exercises show you how to create greyscale and RGB image mosaic
algorithms.
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The ER Mapper Image Display and Mosaic Wizard provides the easiest and
most efficient way of mosiacing images, and should be used where possible. For
illustrative purposes, these exercises will also cover manual methods for
mosiacing images.
What you will
learn...
Before you
begin...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Create a mosaic algorithm by displaying each dataset in its own layer
•
Turn images on or off in a mosaic
•
Specify image priority for the mosaic (which images appear on top of others in the
event of overlap
•
Use the “Create Mosaic” wizard to speed creation of greyscale and RGB mosaics
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
1: Creating a greyscale image mosaic
Objectives
Learn how display several overlapping images in different Pseudocolor layers to
create an image mosaic, and learn to specify image priority in the event of
overlap.
How ER Mapper creates mosaics
To create a mosaic of images, you need to create an algorithm that has each image
loaded in its own layer (or set of layers for RGB). ER Mapper automatically
displays each image in its correct geographic position relative to other images in
the algorithm. (Each image must previously have been rectified to the same datum
and map projection.) Since each image is loaded in a separate layer, you can adjust
contrast and other display qualities of each image independent of other images.
Note: The sample airphotos used in the following exercise were previously rectified to
the same map projection, so they can be displayed together in a mosaic.
Open a new image window and the Algorithm dialog
1 On the main menu, click the Edit Algorithm
button.
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An image window and the Algorithm dialog box appear.
Edit Algorithm button
2 Select the Surface tab, then select greyscale from the ‘Color Table’ menu.
This tells ER Mapper to display an image in greyscale.
3 Select the Layer tab again.
Display the Geocoding toolbar
1 On the main menu, select Geocoding from the Toolbars menu.
The Geocoding toolbar buttons are added to the main menu. You will use these for
fast access to zooming options.
Load a dataset into the Pseudo layer
1 In the process diagram, click the Load Dataset
button.
Load Dataset button
The Raster Dataset file chooser dialog box appears.
2 From the Directories menu, select the path ending with the text /
examples.
3 Double-click on the ‘Functions_and_Features’ directory and then doubleclick on the ‘Compression’ directory.
4 Click once on the dataset ‘San_Diego_Airphoto_34_compressed.ers’ to
select it, then click the Apply button.
ER Mapper loads the dataset into the Pseudocolor layer and leaves the The Raster
Dataset dialog open (you will use it load additional datasets).
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Note: If you plan to load multiple datasets in an algorithm, it is sometimes easier to leave
the Raster Dataset dialog open until you are finished. This saves you the time of
opening the file chooser and navigating to the directory each time.
This airphoto dataset is a compressed copy of the same image you used in the
rectification exercise. It has been rectified to the UTM map projection, and is one
of four sample airphotos you will use to create a mosaic. The airphotos have been
compressed with ECW (Enhanced Compression Wavelet) compression, which
creates a data (.ecw) and header (.ers) file for each image. You can select either of
the two because the .ecw file also contains the geocoding information. The .ers file
must have a corresponding .ecw file but you can have a .ecw file without a .ers file.
5 Change the layer label text to read NW airphoto.
Create a mosaic by adding a second adjacent airphoto
1 Click the Duplicate
button.
click Duplicate
A second ‘NE airphoto’ layer is added below the first one. The second Pseudo
layer is an exact copy of the first one, so it already has the ‘NE_photo’ dataset
loaded.
2 In the Raster Dataset dialog, click once on the dataset
‘San_Diego_Airphoto_36_compressed.ers’ to select it, then click the
Apply this layer only button.
ER Mapper loads the dataset into only the lower (copied) layer and leaves the
Raster Dataset dialog open.
Note: Since both the original and copied layers contained the same dataset (‘NE_photo’),
you must use the Apply this layer only button to load the new dataset into only
the currently selected layer. Apply or OK would have loaded the ‘NW_photo’
dataset into both layers.
3 On the Geocoding toolbar, click the Zoom to All Datasets
button.
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ER Mapper zooms out to show the full extents of both airphotos. The ‘NE_photo’
dataset is on the right (east side) and the ‘NW_photo’ dataset is on the left.
Tip:
Zoom to All Datasets zooms out to the extents of all datasets referenced in the
algorithm, which includes the full extents of a mosaic if two or more adjacent
images are loaded.
4 Change the lower layer label text to read NE airphoto.
Add the third airphoto to the mosaic
1 Click the Duplicate
button.
A copy of the ‘NE airphoto’ layer is added below the original.
2 In the Raster Dataset dialog, click once on the dataset
‘San_Diego_Airphoto_37_compressed.ers’ to select it, then click the
Apply this layer only button.
ER Mapper loads the new dataset into only the lower (copied) layer.
3 On the Geocoding toolbar, click the Zoom to All Datasets
button.
ER Mapper zooms out to show the full extents of all three airphotos. The
‘SW_photo’ dataset is on the lower left (southwest) portion of the mosaic.
4 Change the lower layer label text to read SW airphoto.
Add the fourth (and final) airphoto to the mosaic
1 Click the Duplicate
button.
A copy of the ‘SW airphoto’ layer is added below the original.
2 In the Raster Dataset dialog, click once on the dataset
‘San_Diego_Airphoto_39_compressed.ers’ to select it, then click the OK
this layer only button.
ER Mapper loads the new dataset into only the lower (copied) layer and close the
Raster Dataset dialog. (You are using OK this layer only to close the dialog
since this is the final image in the mosaic.)
3 On the Geocoding toolbar, click the Zoom to All Datasets
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Chapter 7#Assembling image mosaics#z 1: Creating a greyscale image mosaic
ER Mapper zooms out to show the full extents of all four airphotos. The
‘SE_photo’ dataset is on the lower right (southeast) portion of the mosaic.
Newport Beach is the harbor on the Pacific Ocean in the lower-left area of the
mosaic.
4 Change the lower layer label text to read SE airphoto.
Note: There is an obvious darkening effect in the lower portions of the two northern
airphotos. This is typical of aerial photography, and ways to correct for this are
discussed later.
Turn the northwest (upper left) image on and off
1 Right-click on the ‘NW airphoto’ layer, and select Turn Off.
Since its layer is turned off, the northwest airphoto is no longer included in the
mosaic.
2 Turn the ‘NW airphoto’ layer on again.
The northwest airphoto redisplays in its appropriate geographic position again.
This shows how images can be added or subtracted from a mosaic simply by
turning their layers on or off.
Change the display priority of the southern images
Right now, the two northern airphotos are higher in the layer list than the two
southern airphotos. This means that where the southern and northern photos
overlap, the data from the northern photos will be displayed.
1 Drag and drop the two southern layers until they are both above the two
northern layers.
drag and drop to
reorder layers
The airphotos in the two southern layers now have display priority over those in
the two northern layers below them.
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Tip:
An alternative way to move layers is to select them, then use the Move Up
Move Down
or
buttons above them.
The data from the two southern airphotos displays on top of the data from the two
northern airphotos where overlap occurs between the images.
When displaying two or more images in a mosaic algorithm, the image in the top
layer in the layer list appears on top of all others when the algorithm is processed.
The image in the lowest layer has the lowest priority and will only be visible in
areas where there is no overlap from other datasets in layers above it. By adjusting
to order of layers, you can set which datasets appear on top of others in areas
where they overlap.
Zoom in to the geographic extents of any airphoto
1 From the View menu, select Geoposition... (or click the
Algorithm dialog).
button on the
The Algorithm Geoposition Extents dialog opens.
2 Select the Zoom tab.
3 In the Algorithm dialog, select the ‘SW airphoto’ layer.
4 Click the Current Datasets button.
ER Mapper zooms in to the full geographic extents of the image in the current
layer (the southwest airphoto).
5 In the Algorithm dialog, select the ‘NE airphoto’ layer.
6 Click the Current Datasets button.
ER Mapper zooms in to the geographic extents of the northeast airphoto. This
feature lets you instantly zoom to the extents of any raster dataset(s) in the
currently selected layer, so it is very useful for mosaic algorithms.
7 Click Close on the Algorithm Geoposition Extents dialog to close it.
Close the mosaic image window
1 On the main menu, select Close from the File menu.
The mosaic image window closes (File/Close closes the active image window).
The contents of the Algorithm dialog also clear to indicate that no algorithm is
currently open.
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2: Creating mosaics automatically
Objectives
Learn how to speed the creation of greyscale and RGB mosaic algorithms using
the Image Display and Mosaic Wizard.
Start the Create Mosaic Algorithm wizard
1 On the Common Functions toolbar, click the Image Display and
Mosaicing Wizard
button.
The Select files to display and mosaic page of the Image Display and
Mosaicing Wizard opens
2 Click the Load Image
button.
The Select File dialog opens.
3 From the Directories menu (on the Select File dialog), select the
\examples path.
4 Double_click on the ‘Functions_and_Features’ directory to open it.
5 Double_click on the ‘Compression’ directory.
6 Double-click on the image dataset
‘San_Diego_Airphoto_34_compressed.ers’ to select it.
This is the same compressed airphoto that we used in the previous exercise.
7 Select the following options on the wizard page:
Display image in 2D
Image will be displayed in a 2D mode.
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Manually set display method
Enables you to set how the image is to be displayed. If
you do not select this option, the wizard will set the
display method.
Mosaic all files of this type
The wizard will search for files of the same type and
automatically mosaic them.
Manually set mosaic method
Enables you to set how the images are to be mosaiced. If
you do not select this option, the wizard will set the
mosaicing
8 Click on the Next> button to go to the next wizard page.
Select file types to mosaic
This page allows you to specify the characteristics and location of image files that
the wizard must search for to mosaic with the image already selected.
1 Select the Cell sizes and Manually set mosaic properties options. Do not
select the other options on the page.
This tells the wizard that the images to be mosaiced must all have the same data
types and number of bands. They are also in the same directory. They can have
different cell sizes.
2 Click on the Next> button to go to the next wizard page.
Select mosaic properties
This page allows you to specify properties of the mosaiced image.
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1 Select the Feather blend mosaic between images options. Do not select
the other two options.
To simplify the exercise, we will not be defining and using stitch regions.
2 Click on the Next> button to go to the next wizard page.
Select display method
This page allows you to specify how you want the mosaiced image to be displayed.
1 Select the Greyscale display option and Manually select display method
properties.
2 Click on the Next> button to go to the next wizard page.
Select display band
This page allows you to select the image band to display as a greyscale.
1 Select band ‘B1:Red’ from the drop-down menu.
This specifies that the Red band of the image is to be displayed as Greyscale.
2 Click on the Next> button to go to the next wizard page.
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Mosaic and display the images
The wizard searches the current directory and mosaics and displays the following
images:
•
San_Diego_Airphoto_34_compressed.ers
•
San_Diego_Airphoto_36_compressed.ers
•
San_Diego_Airphoto_37_compressed.ers
•
San_Diego_Airphoto_39_compressed.ers
1 For the moment, leave the Image wizard has finished page open.
2 Drag the lower border of the image window downward about 50%.
3 Right-click in the image window, select Quick Zoom, then Zoom to All
Datasets.
ER Mapper zooms out to show the full extents of all four airphotoimages.
Since this image mosaic is taller than it is wide, increasing the window’s width
would have created a large unfilled area on the right side. This is an example of
shaping the window to best fit a particular image display.
4 On the main menu, click the Edit Algorithm
button.
The Algorithm dialog box opens.
You now have a algorithm that displays band 1 of each dataset as a greyscale image
mosaic.
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5 If necessary, use the Move Up and Move Down
buttons to
arrange the layers so that they are as shown in the diagram above.
Turn the top image on and off
1 Right-click on the top ‘Pseudo Layer’ and select Turn Off.
Only the top right, bottom leeft and bottom right images display (since the top left
image is turned off).
2 Right-click on the top ‘Pseudo Layer’ and select Turn On.
The top left image redisplays in its appropriate geographic position again. Any
images in a mosaic can be displayed or not displayed by turning their layers on or
off.
Zoom in to the geographic extents of any image dataset
1 Widen the image window
2 Select the top ‘Pseudo Layer’ (‘San_Diego_Airphoto_34_compressed’) in
the algorithm.
3 Right-click in the image window, select Quick Zoom, then Zoom to
Current Dataset.
ER Mapper zooms in to the full extents of the
‘San_Diego_Airphoto_34_compressed’ dataset (but also displays part of the
lower dataset that occupies the same extents).
Zoom to Current Dataset lets you instantly zoom in or out to the extents of any
raster image dataset(s) in the currently selected layer, so it is very useful for mosaic
algorithms.
2: Creating an RGB image mosaic
Objectives
Learn how display several overlapping images in different sets of red, green, and
blue raster layers to create an RGB image mosaic.
We use the Image Display and Mosaicing wizard to re-display the existing
greyscale mosaiced image as an RGB image.
The final page of the wizard should still be open from the previous exercise.
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Change the image display method
1 Select the Back to Change display method button from the still open
Image Wizard has finished wizard page.
2 On the Select display method page, select the Red Green Blue option.
3 Click on the Next> button to go to the next wizard page.
4 Select RGB 123 as the Red Green Blue display mode type.
This option allocates band 1 to Red. band 2 to Green and Band 3 to Blue.
5 Click on the Next> button to mosaic and display the images, and to go to
the final wizard page.
The wizard will now display the mosaiced image in RGB mode.
6 Click on the wizard Finish button to exit the wizard. Do not close the image
window yet.
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Tip:
In RGB mosaic algorithms, each group of red, green and blue layers act together as
a set. Therefore, you normally want to keep them grouped together in the layer list
in the Algorithm dialog. (To see which dataset is loaded into a particular layer,
select the layer–the name is shown above the process diagram.)
layers for
NW_photo
layers for
NE_photo
process diagram for selected
layer (green layer of NE_photo)
layers for
SW_photo
layers for
SE_photo
Save the mosaic algorithm to disk
1 From the File menu (on the main menu), select Save As....
The Save As... file chooser dialog opens.
2 In the Files of Type: field, select ‘ER Mapper Algorithm (.alg)’
3 From the Directories menu (on the Open dialog), select the path ending
with \examples.
4 Double-click to open the directory named ‘airphoto_training.’
5 In the Save As: text field, type the following filename:
airphoto_mosaic
This name denotes that it is a mosaic of airphots.
6 Click OK to save the algorithm.
Your mosaic algorithm is now saved to an algorithm file on disk.
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Close all image windows and dialog boxes
1 Close both image windows by selecting Close from the File menu.
2 Click Close on the Algorithm dialog to close it.
Only the ER Mapper main menu should be open on the screen.
What you
learned
156
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Create a mosaic algorithm by displaying each dataset in its own layer
•
Turn images on or off in a mosaic
•
Specify image priority for the mosaic (which images appear on top of others in the
event of overlap
•
Use the “Create Mosaic” wizard to speed creation of greyscale and RGB mosaics
ER Mapper Workbook - Airphoto Mosaic Applications
8
Color balancing
images
This chapter explains techniques to correct or normalize changes in brightness
across single images that cause some areas to appear noticeably brighter or darker
than others. It also discusses ways to balance the overall contrast of a mosaic of
images to make them appear as a single image.
About color balancing
When creating a mosaic of images, there are two primary issues to be addressed
that help make the mosaic appear to be a single, seamless image:
Note: The Color Balancing Wizard balances and matches colors automatically, and
does not require any manual intervention. The descriptions and exercises in this
chapter have been included to provide an understanding of the color balancing
process.
•
correcting shifts in brightness or color within individual images
•
balancing the overall contrast of the mosaic (normalizing the contrast of all images
to a common level)
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Chapter 8#Color balancing images#z About color balancing
When balancing the brightness and contrast of images (and mosaics of images), it
is often easier to work with a single band of the image at a time in greyscale. This
is because subtle brightness and contrast adjustments are more difficult to carry out
when working with three components (red, green and blue) than one component
(red, for example). For example, you might start by creating a balanced mosaic
showing only the red band of each airphoto. Then do the same for the green and
blue components, and add them back together into an RGB mosaic at the end.
Although this is not the only approach, it is the one that will be used in these
exercises.
Brightness shifts and vignetting
Airphotos sometimes exhibit shifts in brightness or intensity across the image, for
example one side of an image is noticably darker than another. This intensity “roll
off” problem is due to lens refraction of the camera, and usually results in
darkening toward one side or toward the edges of the image (“vignetting”). It is
usually desirable to try to correct brightness shifts in airphotos because they will
be more noticeable when the images are displayed side-by-side in a mosaic.
Note: Not all airphotos will exhibit noticeable brightness shifts. This chapter explains
how to correct for them if your airphotos exhibit these characteristics.
original photo with top to bottom
brightness shift (light to dark)
intensity normalized across photo
using linear ramp formula
There are three main types of brightness or color shifts in airphotos:
•
158
linear brightness shifts–the brightness changes at a fairly constant rate from one
side of an image to the other
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Chapter 8#Color balancing images#z Hands-on exercises
•
vignetting (hot spots)–a central portion of the image is noticably brighter, and the
image darkens as you move out toward the edges
•
haze (blue cast) corrections–some airphotos (usually natural color) have a bluish
cast or tint, either overall or outward from the center
Note: See the sections “Vignetting (“hot spot”) corrections” and “Haze (blue cast)
corrections” at the end of this chapter for more details on techniques to remove or
minimize their effects.
Overall contrast balancing
Once the brightness shifts have been corrected in individual photos (if needed), the
next issue is creating a mosaic and balancing the contrast of each image relative to
the others. This is an important step to help make the color and brightness
consistent across the entire mosaic.
initial mosaic showing contrast
differences between images
contrast balanced mosaic created
using histogram matching
One common technique for doing this is called histogram matching. This
technique matches the output histograms (transforms) for all images to one image
which is chosen as the reference image. You will learn to do this in this exercise.
Hands-on exercises
These exercises show you how to use ER Mapper’s formulas feature to correct
brightness shifts across an image.
What you will
learn...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
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Before you
begin...
•
Enter and modify a formula in ER Mapper
•
Use special formulas to correct brightness shifts in an image
•
Create a greyscale mosaic of individually corrected images
•
Use histogram matching to balance the contrast of the mosaic
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
1: Using brightness shift formulas
Objectives
Learn how to apply a formula to correct a brightness shift in an image, and how to
modify the formula to suit problems in specific airphotos.
Create a greyscale image of the San Diego 36 airphoto
1 On the main menu, click the Image Display and Mosaic Wizard
button.
Image Display and Mosaic
Wizard button
The Select files to display and mosaic page of the Image Display and
Mosaic Wizard opens
2 Click the Load Image
button.
The Select File dialog opens.
3 From the Directories menu (on the Select File dialog), select the
\examples path.
4 Double_click on the ‘Applications’ directory to open it.
5 Double_click on the ‘Airphoto’ directory.
6 Open the ‘1_Geocoding’ directory.
7 Double-click on the image dataset ‘San_Diego_Airphoto_36_rectified.ers’
to select it.
This dataset is a high resolution image covering a portion of San Diego.
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8 Select the following options on the wizard page:
Display image in 2D
Image will be displayed in a 2D mode.
Manually set display method
Enables you to set how the image is to be displayed. If
you do not select this option, the wizard will set the
display method.
9 Click on the Next > button to go to the next dialog box.
The wizard will open the Select display method dialog box for you to specify
the display method.
Select display method.
You have the choice of four different display methods:
Greyscale
Loads a single band into a pseudocolor layer using the
greyscale Color Table.
Red Green Blue
Loads three of the bands into RGB layers.
Sunshade
Loads a single band into a greyscale pseudocolor layer
with sun-shading enabled.
Colordrape
Drapes a pseudocolor layer over an intensity layer with
the sun-shading enabled.
10 Select the Greyscale option and Manually select display method
properties to specify how the image is to be displayed.
11 Click on the Next > button to go to the next dialog box.
Select display method
The Select How to display using Greyscale wizard dialog box allows you to
select the image bands that are to be displayed as Red Green and Blue.
12 In the Band to display: field, select ‘B1:Red’ so that band 1 (Red ) will be
displayed as greyscale.
13 Click on the Next> button to go to the final dialog box.
The wizard will process the image and display it with the transform clip limits set
to 99%.
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14 In the Image Display and Mosaicing Wizard has finished dialog box,
select Finish to close the wizard.
ER Mapper creates a simple pseudocolor algorithm that displays the red band
(band 1) of the San Diego 36 airphoto as a greyscale image. This airphoto exhibits
a subtle, but noticable brightness shift from top to bottom (darker at the bottom).
These types of shifts, even subtle ones, can be very noticable in mosaics of several
images.
Load the linear ramp formula into the Pseudo layer
1 On the main menu, click the Edit Algorithm
Algorithm dialog box.
2 In the process diagram, click the Edit Formula
button to open the
button.
Edit Formula button
The Formula Editor dialog box opens. (If needed, move it right so it does not
cover the image window.) This dialog lets you load standard formulas supplied
with ER Mapper, and create your own formulas for specific image processing
tasks.
3 From the File menu (on the Formula Editor dialog), select Open.
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The Open Formula dialog appears. This dialog gives you access to directories
containing standard formulas supplied with ER Mapper.
4 From the Directories menu, select the path ending with \formula.
5 Double-click to open the directory named ‘mosaic’ to open it.
6 Double-click on the formula ‘linear_ramp.frm’ to load it.
The “linear_ramp’ formula is loaded in the Formula Editor dialog. This dialog
has three major areas:
generic formula–load
or enter formula text
relations area–define
relationships between
generic formula parms
and dataset bands, etc.
specific formula–final
formula to be executed
Adjust parameters of the linear ramp formula
1 Click the Comments button on the Formula Editor dialog.
Comments about the use of the linear ramp formula are displayed.
The ‘linear_ramp’ formula is designed to apply a gradual change in brightness (a
“ramp”) across an image. It can therefore be used to counter the brightness shift
problem and normalize the brightness to a constant level across this image.
This formula has three main controls:
•
INPUT1–controls the dataset band on which the formula will operate, band 1 of the
image (red) in this case.
•
X_Correction and Y_Correction–two parameters that control the direction and
strength of the brightness shift operation
2 Click the OK on the Formula comments dialog to close it.
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3 In the Formula Editor dialog, click the ‘Variables’ button in the relations
area.
click Variables button
fields to assign values
to variables
The contents of the relations area change to show two fields for entering values for
the X_Correction and Y_Correction variables in the linear ramp formula.
4 Change the value of the ‘Y_Correction’ field to 0.4 then press Enter or
Return to validate.
Note: After changing a variable value, make sure you press Enter or Return on your
keyboard to have ER Mapper validate and check the value.
5 Click the 99% Contrast Enhancement
button.
ER Mapper runs the algorithm and applies an overall shift in brightness to the
image. (The top becomes slightly darker and the bottom slightly lighter to make
the overall brightness the same across the airphoto.)
Note: You are using the 99% Contrast Enhancement
button here because each
set of variable values creates slightly different output data ranges. 99% Contrast
Enhancement
compensates for that by setting transform limits to actual
each time to give a good contrast enhancement automatically.
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Try other correction values to see how the formula works
The linear ramp formula is very versatile and can be used to adjust the brightness
shifts top-to-bottom, side-to-side, and diagonally across an image. To do this,
adjust the values for X_CORRECTION and/or Y_CORRECTION variables as
needed. Suggested values range from 0.4 to -0.4, but larger values may also be
useful.
X_Correction - adjust brightness in the left to right direction: Example: 0.3
lightens the right side relative to left, -0.3 the opposite.
Y_Correction - adjust brightness in the top to bottom direction: Example: 0.3
lightens the bottom relative to top, -0.3 the opposite.
By using both variables, you can adjust brightness diagonally across the image.
1 Change the variable values as follows (press Return or Enter after):
X_Correction = 0.4
Y_Correction = 0.0
2 Click the 99% Contrast Enhancement
button.
The right side of the image lightens relative to the left.
3 Change the variable values as follows (press Return or Enter after):
X_Correction = 0.4
Y_Correction = 0.4
4 Click the 99% Contrast Enhancement
button.
The lower-right corner of the image lightens relative to the upper-left.
5 Change the variable values as follows (press Return or Enter after):
X_Correction = -0.4
Y_Correction = -0.4
6 Click the 99% Contrast Enhancement
button.
The upper-left corner of the image lightens relative to the lower right.
Reset the correction values to the best for this image
1 Change the variable values as follows (press Return or Enter after):
X_Correction = 0.0
Y_Correction = 0.4
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2 Click the 99% Contrast Enhancement
button.
The lower part of the image lightens relative to the upper part. This is the best
overall adjustment for this particular image, since its primary problem is a light-todark shift from top-to-bottom.
3 Click the Close on the Formula Editor dialog to close it.
Note: Each image (or group of related images) will have its own brightness shift
characteristics. You should try various settings to see which gives the best results
on your airphotos. There is always a compromise you must reach between
optimizing contrast in different parts of the image, so keep this in mind. In
addition, there are other formulas for correcting “hot spots” and bluing at the
edges. See the sections “Vignetting (“hot spot”) corrections” and “Haze (blue cast)
corrections” at the end of this chapter for more details.
2: Create a mosaic of balanced images
Objectives
Learn how to create a mosaic of corrected images, and use histogram matching to
balance the overall contrast and brightness of the mosaic.
Duplicate the layer to display another dataset
Since the current layer already has your formula loaded, it is easiest to duplicate it
an load the different dataset.
1 On the Algorithm dialog, click the Duplicate
button.
click Duplicate
The Pseudo layer is duplicated.
2 Click the Load Dataset
button in the process diagram.
The Raster Dataset dialog opens. Move it next to the Algorithm dialog so both
dialogs are visible.
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3 From the Directories menu (on the Raster Dataset dialog), select the path
ending with \examples.
4 Double_click on the ‘Applications’ directory to open it.
5 Double_click on the ‘Airphoto’ directory.
6 Open the ‘1_Geocoding’ directory.
7 Click once on the dataset ‘San_Diego_Airphoto_34_rectified.ers’ to select
it, then click Apply this layer only.
ER Mapper loads the ‘San Diego 34’ dataset into only the selected layer.
Note: Since you duplicated the original layer, both it and the copy had the same dataset
loaded. Since you want to load the new dataset into only the copied layer, you must
use Apply this layer only or OK this layer only. (OK, Apply or doubleclicking would load the new dataset into both layers.)
Zoom out to the extents of both airphotos
1 Right-click in the image window, and from the shortcut menu select Quick
Zoom, then Zoom to All Datasets.
ER Mapper zooms out to show the full extents of all four images in the greyscale
airphoto mosaic. (Right-clicking in the image window gives you quick access to
many of the same options on the main menu.)
2 Click the 99% Contrast Enhancement
button.
ER Mapper runs the algorithm and automatically optimizes the contrast of the two
individual images in the mosaic.
Even though each photo has the linear ramp correction applied, you can see the
seams between airphotos by the difference in overall brightness and contrast
between them. This is typical of mosaics because each airphoto dataset has a
different range of values than the others.
Assign the western photo display priority in the mosaic
Currently the eastern airphoto (36) covers the western airphoto where there is
overlap because it is higher in the layer list. Now is the time when you decide
which photo will appear on top of the other where there is overlap.
1 Select the surface layer in the algorithm (the green icon next to
[Ps]:Pseudocolor).
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Process diagrams for both layers display in the Layer tab area. This lets you see
which dataset is loaded into each layer (above the Load Dataset
button.)
2 Change the order of layers so that the airphotos are in the following order
(by dragging and dropping the layers or using the Move Up
Down
and Move
buttons):
San_Diego_Airphoto_34_rectified.ers
San_Diego_Airphoto_36_rectified.ers
The eastern airphoto is now covered by the western photo. For this particular set of
images, this configuration achieves a better overall contrast balance and creates the
most visually pleasing mosaic.
Tip:
When working with your own data, you would typically try different
configurations until you find the one that looks best. For example, changing the
priority can help minimize contrast differences, or you might want to make sure a
problem area in one image is covered by a better image if possible.
Histogram match the airphotos to the west photo
Histogram matching tries to make the output histogram for several images match
the output histogram of a reference image. By doing this, the overall differences in
contrast between a set of images can be minimized.
1 Select the layer containing the ‘San_Diego_Airphoto_36_rectified.ers’
dataset (the second layer).
This will be the reference image to which the contrast of the other image will be
matched.
2 Click the Edit Transform Limits
button in the process diagram.
Edit Transform Limits button
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The Transform dialog opens showing the histogram for the ‘SE_photo’ dataset.
The solid black histogram is the input (dataset) histogram, and the thin grey
histogram line is the output (screen) histogram:
output histogram
The output histogram shows the distribution of colors in the screen image (grey
shades in this case). Histogram matching will attempt to make the output
histograms for the other three dataset layers match this one.
3 In the Transform dialog, click the Histogram match
button.
Histogram match button
4 A dialog appears explaining the histogram match function–click Yes to
continue.
ER Mapper reprocesses the mosaic image and adjusts the contrast slightly so that
all four images have similar contrast characteristics. (The transform lines for the
other three Pseudo layers in the algorithm were automatically changed to make
their output histograms match that of the reference dataset.)
5 In the Transform dialog, click the
other layer.
button to view the transform for the
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Notice that the other layer has a complex transform line defined–this is the result
of the histogram matching operation. (The transform for the reference layer was
not changed, only the other layer.)
6 Click Close on the Transform dialog to close it.
Note: When working with your own data, you would typically experiment by trying
different datasets as the reference dataset until you achieve the best overall result.
Usually your reference image should be one that contains a mixture of the types of
surface cover found in the entire mosaic (urban, farmland, water, etc.). To try
different datasets, first click the 99% Contrast Enhancement
button to set
all the transforms back to a 99% clip on limits, then select the new reference layer
and click the Histogram match
button.
Enter a description for the entire algorithm
1 In the Algorithm dialog, change the text in the Description field to read
Red band mosaic - balanced and histogram matched
This text now becomes a brief description for the entire algorithm.
Save the balanced red bands algorithm to disk
1 From the File menu (on the main menu), select Save As....
The Save Algorithm file chooser dialog opens.
2 From the Directories menu, select the path ending with the text
\examples.
3 Double-click on the directory named ‘airphoto_training’ to open it.
4 In the Save As: text field, type the following filename:
Red_bands_balanced_mosaic
This name denotes that it contains a balanced mosaic of the red band images.
5 Click OK to save the algorithm.
Your balanced red band algorithm is now saved to an algorithm file on disk.
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Tip:
You will also have to define similar algorithms for the green and blue bands of the
image mosaic. Since you will next perform some other processing to help remove
seam lines, it is easier to do this first to the red band mosaic, then duplicate the
processing for the green and blue band mosaics before assembling the final RGB
color mosaic.
Close all image windows and dialog boxes
1 Close the image window by selecting Close from the File menu.
2 Click Close on the Algorithm dialog to close it.
Only the ER Mapper main menu should be open on the screen.
What you
learned
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Enter and modify a formula in ER Mapper
•
Use special formulas to correct brightness shifts in an image
•
Create a greyscale mosaic of individually corrected images
•
Use histogram matching to balance the contrast of the mosaic
Other color shift corrections
In the previous exercise, you used the ‘linear_ramp’ formula to correct brightness
shifts because that was the appropriate adjustment for the four sample images.
However, there are also corrections for vignetting and haze (blue cast) removal
that you may consider using if your airphotos exhibit these problems.
Vignetting (“hot spot”) corrections
Instead of a gradual shift in brightness or color from one side to another, some
airphotos have a general darkening toward the edges outward from a central
brighter area (the “hot spot”). This effect is called vignetting, and is due to lens
refraction in the camera. (Special antivignette filters are sometimes used on the
camera to minimize this effect.) This type of correction is a bit more complicated
mathematically, but is still fairly easy to implement in ER Mapper.
To use the hot spot formula technique, first display your image in an RGB
algorithm, then follow these steps:
1 Select Cell Coordinate from the View menu.
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The Cell Coordinate dialog opens.
2 In the image, click in the center of the hot spot, and note the cell location in
Dataset X,Y coordinates.
You will use this X,Y cell location in the hot spot formula to tell ER Mapper where
the hot spot originates on the image.
3 Click the Edit Formula
button, and load the formula
‘hot_spot_correction.frm’ in the ‘mosaic’ directory.
This formula has four variables that allow you to specify the location of the hot
spot, and apply a correction factor to brighten other parts of the image relative to
the hot spot.
4 On the Formula Editor dialog, click the ‘Variables’ button and set the
values of the four variables as needed for your image:
X_Center - the X (column) cell location of the hot spot in dataset X,Y coordinates
(from step 2)
Y_Center - the Y (row) cell location of the hot spot in dataset X,Y coordinates
(from step 2)
X_Factor - a factor controlling the amount of brightness increase in areas right
and left of the hot spot; suggested values are 0.1 to 0.35.
Y_Factor - a factor controlling the amount of brightness increase in areas above
and below the hot spot; suggested values are 0.1 to 0.35.
5 After balancing the image, save the algorithm.
You can use this a s template to correct other hot spot images, or copy the layers
and add other datasets to create a mosaic of hot spot corrected images.
Haze (blue cast) corrections
The blue band of natural color airphotos is very sensitive to atmospheric scattering
due to pollution and haze in the atmosphere. This scattering effect often gives the
photo a bluish cast or tint, either over the entire photo, or toward the edges
(vignetting). There are some special techniques that may be applied only to the
blue band image to compensate for this.
(Haze generally does not affect the green and red bands of natural color airphotos,
and does not affect color IR airphotos since they do not image in the blue
wavelengths. Black and white visible wavelength airphotos often use special
“minus blue” filters to block the blue wavelengths and prevent this problem.)
Haze can also affect the clarity of features in the blue band image, and sometimes
makes interpretation of detail difficult. Unfortunately there is no way to correct
this problem because it is inherent in the original airphoto data. (This effect can be
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seen in the northern parts of the sample training airphotos.) Usually the effect is
not too noticeable in RGB color airphotos because the clarity in the red and green
bands tends to hide problems in the blue band to some degree.
Overall blue cast removal
Natural color images often have an overall blue cast to them, for example what
should be green vegetation looks more cyan than green. Because the blue
wavelengths of light are heavily scattered by the atmosphere, the blue band data
often has increased overall brightness relative to the green and red bands. This can
be seen in the histograms of the three bands, where the lowest value for the blue
band data is usually much higher than the green or red bands:
red band
lowest value = 8
green band
lowest value = 35
blue band
lowest value = 69
scattering increases
blue band values
Usually applying a 99% clip transform to the image will remove this problem, as it
will set the transform line to the base of the histogram in each band. If this does not
occur, you can apply a stronger clip (97 or 95% for example), or manually drag the
transform lines to the base of the histogram in each layer.
The gap between the origin (left side) and the base of the histogram and the
histogram is generally considered to be the contribution of atmospheric scattering
recorded on film by the camera. (The green band also has some, but less, of this
effect).
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Tip:
Applying a 99% clip transform to the data works best if you first zoom in to crop
off any black edges that may have been scanned as part of the airphoto. The black
edges tend to contain low or zero data values that will not be clipped off if
processed as part of the image data.
Blue vignetting removal
Sometimes the blue cast or tint increases toward the edges of the image, and the
interior portions look normal (a vignetting effect). Following is one way to try to
remove the blue cast from only the affected areas.
1 Define and name a region polygon within the image that contains the
“normal” color you expect to see (without the blue cast).
This is typically near the center of the image. Make the region as large as possible
without including any areas with a noticeable blue cast. You will use the
characteristics of this area to help correct other areas affected by the blue cast.
Note: Chapter 8 contains information about defining regions and using them in a formula
as you are asked to do here.
2 Select Cell Coordinate from the View menu.
The Cell Coordinate dialog opens.
3 In the image, click inside the region you defined and note the cell location
of the area with the best “normal” RGB color in Dataset X,Y coordinates.
You are looking for the location (within the overall region) of the best overall color
balance in the image. You will use this X,Y cell location in the correction formula.
4 Select the Blue layer in your algorithm, then click the Edit Formula
button in the process diagram.
5 Load the formula ‘anti_vignetting.frm’ in the ‘mosaic’ directory.
6 Edit the formula text to add the following before the it (where <formula> is
the existing anti vignette formula):
IF INREGION(REGION1) THEN INPUT1 ELSE <formula>
This formula tells ER Mapper that “if the data falls inside the good area region,
then display it without changes, else apply the antivignetting formula (to the area
outside the region).”
7 In the Formula dialog, click on the ‘Regions’ option button, then select your
good region name from the ‘REGION1’ drop-down list.
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8 In the Formula dialog, click on the ‘Variables’ option button, then set the
variables to the following values:
OFFSET- a factor controlling the amount of offset to the blue histogram (set to
zero for now, you will adjust this later).
X_Center - the X (column) cell location of the “good color” area in dataset X,Y
coordinates (from step 3)
Y_Center - the Y (row) cell location of the “good color” area in dataset X,Y
coordinates (from step 3)
X_Factor - a factor controlling the amount of blue color adjustment in areas left
and right of the good region; suggested values are 0.1 to 0.35. (Try one of these
values, you will need to experiment to get it right.)
Y_Factor - a factor controlling the amount of blue color adjustment in areas above
and below the good region; suggested values are 0.1 to 0.35. (Try one of these
values, you will need to experiment to get it right.)
The entire image should appear with a slight blue cast.
9 Click the Edit Transform Limits
analyze the blue band histogram.
button in the process diagram, then
The histogram should have two peaks, one representing the “good” area and
another (to the right) representing the area affected by the blue cast. Note the
difference in data values between the two peaks (usually this is about 60 to 80 but
varies with each image). This is the value for the OFFSET variable.
10 Enter the valued determined in step 10 for the ‘OFFSET’ variable in the
Formula dialog.
11 Continue to adjust the OFFSET, X_Factor and Y_Factor variables until the
image has a constant blue cast across it (no noticeable color shift).
12 Finally, adjust the transforms for the red and green layers until the entire
image appears in the “normal” RGB color you want.
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9
Removing seam
lines
This chapter explains techniques you can use to minimize or remove visible seams
between images in a mosaic. This may not always be necessary, but it helps create
a “seamless” final mosaic.
Note: The Color Balancing Wizard will do all that is described in this chapter
automatically. These descriptions are included to give you an understanding of the
processes involved.
About regions and feathering
After the previous exercise, you have learned to correct the overall brightness and
contrast problems encountered in creating mosaics. This is the first step in
balancing the overall contrast of the mosaic to help create one continuous,
seamless image. However, there are always minor contrast problems between
adjacent images that cannot be removed, and slight mismatches of features along
seam lines due to slight errors in the rectification of the images. To create the best
possible mosaic, ER Mapper has two additional features that help you achieve a
final “seamless” look. They are:
•
region polygons to constrain the overlap between images to exact areas
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•
edge feathering to blend images in areas of overlap to remove visible seam lines
Creating hidden stitch line regions to remove seams
One effective technique for removing seam lines is to define a special region for
each image that constrains the area of overlap with other images to a narrow area.
Inside this small area of overlap, ER Mapper’s feathering feature can be used to
blend the two images, thus creating a seamless merge between adjacent images.
You can also create specially shaped regions that create seams between images that
correspond exactly with the border of a specific feature, for example a river.
Since the feathering feature works in across an image (horizontally), it is best to
define specially shaped regions that create a diagonal zone of overlap between the
top and the bottom image. To do this, you need to be able to see the true areas of
overlap (using the RGB or other technique), then define a region for each image:
region polygon for image A
(defines area to be displayed)
image A
true area of
overlap in
images A & B
regions constrain overlap
to only the area common to
both regions; blending
(feathering) occurs only
within this zone
image B
region polygon for image B
(defines area to be displayed)
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For these four sample images, the regions will look like the following diagram
when finished. The goal is to create a narrow zone of overlap between the images
as this will make the feathering feature more effective for blending out seam lines.
image A
image C
feathering occurs only
inside overlap zones
image D
image B
true areas of overlap
in the four images
regions to constrain
areas of overlap
regions can also be used to
cut out edges of airphotos with
fiducial marks or black areas
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Feathering (blending) images in overlap zones
Feathering is an image processing technique that blends or averages the data
values between two image across a zone of overlap. This creates a gradual
transition from one image to another, instead of the sharp boundary between
images if feathering is not used.
natural seam line between images
feathering across image seam
Feathering can also be effective to hide small misalignments between features on
adjacent photos. (However gross misalignments will create a blurred look, and you
should consider rectifying one or both images again to improve this.)
Feathering works best when constrained to fairly small areas of overlap. You can
define these areas using regions as described previously.
Hands-on exercises
These exercises show you how to use ER Mapper’s regions feature to define exact
areas of overlap, and to use edge feathering to minimize seam lines.
What you will
learn...
180
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Display images so that areas of overlap are evident
•
Define a region polygon to constrain areas of overlap
•
Use the region as a mask in a formula
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Chapter 9#Removing seam lines#z 1: Determining areas of overlap
•
Before you
begin...
Use edge feathering to minimize seam lines between adjacent images
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
1: Determining areas of overlap
Objectives
Learn how to view areas of overlap between images as an RGB algorithm, and
concepts behind defining overlap areas for mosaics.
Open the balanced red band algorithm
1 On the main menu, select Open from the File menu.
An image window and the Open dialog appear.
2 From the Directories menu (on the Open dialog), select the path ending
with \examples.
3 Double-click to open the directory named ‘airphoto_training.’
4 Double-click on your ‘Red_bands_balanced_mosaic.alg’ algorithm to open
it.
The balanced greyscale mosaic displays in the image window. This algorithm was
created to view images in greyscale, so it uses the Pseudocolor Color Mode and
two Pseudo layers. By changing the display of this algorithm, you can easily view
areas of overlap between the two images.
Display the two images as red and green
1 Right-click on the ‘[Ps]:Pseudocolor’ icon, then select Red Green Blue.
The surface Color Mode changes to Red Green Blue (indicated in the surface name
[RGB]:Default Surface). The Pseudo layers are crossed out because they are not
valid in RGB mode. You will change them Red, Green and Blue layers next.
Tip:
You can change the Color Mode for the surface either by right-clicking on it, or by
selecting the Surface tab and selecting it there.
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2 Right-click on each of the two layers and change them to Red and Green
layers as shown below:
Change to Red
Change to Green
The mosaic redisplays so each of the images is shown in a different color . Areas
of overlap are clearly visible by the color that results from mixing red and green .
The area of overlap between the images is shown in yellow (since red and green
combine to create yellow). Areas where images do not overlap are shown as either
red or green.
Tip:
This technique is also a good way to evaluate the accuracy of registration between
two images in the area of overlap. For example, where a red and green image
overlap, you will typically see a red or green “halo” around features that do not
align well in the two images. (This is caused by the same feature being slightly
offset in the two images.) Good registration will make features appear as solid
yellow.
Display the images as a greyscale mosaic again
1 Right-click on the ‘[RGB]:Pseudocolor’ icon, then select Pseudocolor.
The surface Color Mode changes to Pseudocolor (indicated in the surface name
[Ps]:Default Surface). The Red and Green are crossed out because they are not
valid in Pseudocolor mode.
2 Right-click on each of the two layers and change them to Pseudo layers:
The mosaic redisplays in greyscale again. As you can see, it is easy to change the
type of display and color mode for an algorithm as needed to help accomplish a
particular task. (In this case, you wanted to see the overlap between images in the
mosaic.)
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Chapter 9#Removing seam lines#z 2: Defining regions to constrain overlap
2: Defining regions to constrain overlap
Objectives
Learn how to define region polygons, how to view areas of overlap between
images, and how to reference regions in a formula to constrain areas of overlap.
Also learn the concepts behind defining overlap areas for mosaics.
You will learn the method used to actually define and name region polygons for
the raster datasets in the mosaic.
Add a vector layer for region definition to the first dataset
1 In the Algorithm dialog, right-click on the lower layer and select Turn Off.
The ‘San_Diego_Airphoto_34_rectified.ers’ image will be the only one to be
displayed.
2 On the main menu (or Algorithm dialog), click the Annotate Vector Layer
button.
The New Map Composition dialog box opens.
3 Select the ‘Raster Region’ option button, then click OK.
The Raster Region option tells ER Mapper that the annotation layer will be used
to create regions for a raster dataset.
ER Mapper opens the Tools palette dialog box containing your vector annotation
tools. Also notice that a new vector layer titled ‘Region Layer’ has been added to
the layer list in the Algorithm window.
Define and name a region polygon
1 On the Tools palette dialog, click on the Polygon
button.
2 Draw a polygon on the by clicking once at each point, then double-clicking
to close the polygon. (Make your polygon fairly large.) The polygon should
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be in the form of a rectangle that covers the entire image apart from half of
the overlap area.
Polygon
Overlap area
The polygon is selected by default when you close it. Since it is selected, you can
now add a color and text attribute to give the polygon a name.
3 On the Tools dialog, double-click the Polygon
Style dialog box.
button to open the Line
4 In the Line Style dialog, click the Set Color button, choose any bright
color, and click OK to close the color chooser.
The polygon redisplays with the new color.
Note: The line width, line style and other controls apply only to vector annotation, so
they are inactive when defining raster regions. You will learn to use the vector
annotation tools later during map composition.
5 Click Close on the Line Style dialog.
6 On the Tools dialog, click the Display/Edit Object Attribute
open the Map Composition Attribute dialog box.
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7 In the Map Composition Attribute dialog, enter the name “west_region”
for your region in the text field at the bottom, then click the Apply button.
2 - then click Apply
1- type a region name
The text is now defined as a the name or text attribute of the polygon. Later you
can refer to the polygon by this name in a formula.
Save the region to the dataset
1 Click Close on the Map Composition Attribute dialog.
2 On the Tools palette dialog, click the Save File
button.
A message dialog appears prompting you to confirm the overwrite of the dataset
header file.
3 Click OK on the overwite message dialog.
A message window appears showing the names of regions that were added to the
dataset header file.
4 Click Close on the ER Mapper Message Window to close it.
The region definition and name is saved to the header file of the
‘San_Diego_airphoto_34_rectified.ers’ dataset.
5 Click Close on the Tools palette dialog to close it.
Add a vector layer for region definition to the second dataset
1 In the Algorithm dialog, right-click on the lower layer and select Turn On.
Right-click on the upper Pseudo Layer and Region layer, and select Turn
Off.
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The ‘San_Diego_Airphoto_36_rectified.ers’ image will be the only one to be
displayed.
2 On the main menu (or Algorithm dialog), click the Annotate Vector Layer
button.
The New Map Composition dialog box opens.
3 Select the ‘Raster Region’ option button, then click OK.
The Raster Region option tells ER Mapper that the annotation layer will be used
to create regions for a raster dataset.
ER Mapper opens the Tools palette dialog box containing your vector annotation
tools. Also notice that a new vector layer titled ‘Region Layer’ has been added to
the layer list in the Algorithm window.
Define and name a region polygon
1 On the Tools palette dialog, click on the Polygon
button.
2 Draw a polygon on the by clicking once at each point, then double-clicking
to close the polygon. (Make your polygon fairly large.) The polygon should
be in the form of a rectangle that covers the entire image apart from half of
the overlap area.
The polygon is selected by default when you close it. Since it is selected, you can
now add a color and text attribute to give the polygon a name.
3 On the Tools dialog, double-click the Polygon
Style dialog box.
button to open the Line
4 In the Line Style dialog, click the Set Color button, choose a different
bright color, and click OK to close the color chooser.
The polygon redisplays with the new color.
Note: The line width, line style and other controls apply only to vector annotation, so
they are inactive when defining raster regions. You will learn to use the vector
annotation tools later during map composition.
5 Click Close on the Line Style dialog.
6 On the Tools dialog, click the Display/Edit Object Attribute
open the Map Composition Attribute dialog box.
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7 In the Map Composition Attribute dialog, enter the name “east_region”
for your region in the text field at the bottom, then click the Apply button.
The text is now defined as a the name or text attribute of the polygon. Later you
can refer to the polygon by this name in a formula.
Save the region to the dataset
1 Click Close on the Map Composition Attribute dialog.
2 On the Tools palette dialog, click the Save File
button.
A message dialog appears prompting you to confirm the overwrite of the dataset
header file.
3 Click OK on the overwite message dialog.
A message window appears showing the names of regions that were added to the
dataset header file.
4 Click Close on the ER Mapper Message Window to close it.
The region definition and name is saved to the header file of the
‘San_Diego_airphoto_36_rectified.ers’ dataset.
5 Click Close on the Tools palette dialog to close it.
Display the region polygons over the image mosaic
Each one of the four sample airphoto images already has an appropriate region
polygon defined to constrain the areas of overlap. Now you will learn how to
display the regions simultaneously for all images in the mosaic.
1 In the Algorithm dialog, turn on all the layers by right-clicking on them and
selecting Turn on.
The two Pseudo and their corresponding Region layers should now be displayed
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Note that each region layer has a different color. This was done to make them easy
to differentiate when displayed together like this. As you can see, the regions are
defined to constrain the area of overlap to a narrow zone as described previously.
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Chapter 9#Removing seam lines#z 3: Feathering images within regions
3: Feathering images within regions
Objectives
Learn how to use formulas to process only portions of images inside region
polygons, and how to turn on feathering to minimize seam lines between images.
Turn off layers for the eastern image
1 Right-click on the ‘San_Diego_Airphoto_36_rectified.ers’ layer, then select
Turn Off. (For both the Region and Pseudo layers).
right-click and turn off layers for
the lower image
Only the western image and its region polygon displays.
Edit the linear ramp formula to reference the region
1 Select the top Pseudo Layer in the layer list.
2 In the process diagram, click the Edit Formula
button.
The Formula Editor dialog box opens. Move it left of the Algorithm dialog and
below the image window (so all three are visible).
You will edit the linear ramp formula so it only operates on and displays the data
inside the region polygon.
3 Edit the formula as follows, where <ramp formula> is the existing linear
ramp formula text already in place:
IF INREGION(REGION1) THEN <ramp formula> ELSE NULL
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Make sure the spaces between words and spelling are exactly as above. When
finished, the formula should look like this:
edit generic formula
as described
4 Click the Apply changes button on the Formula dialog.
ER Mapper verifies the syntax of your formula. (If you receive an error message,
go back a edit the formula as needed, then click Apply changes again.)
This formula tell ER Mapper “if the data is inside the named region, then apply the
linear ramp formula to it, else assign it a value of null.” Any data values (pixels)
assigned a value of null are “masked” from further processing and do not appear
on the image.
Assign the generic “region1” to the ‘west_region’ region
The text you added in parentheses–(region1)–is a generic reference that you can
assign to any region name you defined for your dataset.
1 In the Formula dialog, click on the ‘Regions’ option button.
The relations area of the dialog changes to show the text REGION1 with dropdown menu next to it.
2 Open the ‘REGION1’ menu and select west_region.
This tells ER Mapper to relate the text “REGION1” in the generic formula to the
actual region in your dataset named “west_region.”
Only the portion dataset inside the region polygon displays. Areas outside the
polygon are masked by the formula.
Next you will make this change to the formulas in the other Pseudo layer, so only
the area within its ‘east_region’ region is processed and displayed.
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Save the modified linear ramp formula
Since you want to add the same formula to the other Pseudo layer, one shortcut is
to save the formula. That way, you can load it directly into the other layer without
having to retype the text.
1 From the File menu (on the Formula dialog), select Save As.
The Save Formula file chooser dialog opens. It is already set to the directory
containing the original ‘linear_ramp.frm’ formula, and you will save your
modified version in the same place.
2 In the Save As field, enter the text linear_ramp_inregion then click
OK.
Your formula is now saved to disk and can be reloaded at any time.
Turn on all layers in the algorithm
1 Right-click on both the layers for the lower dataset, then select Turn On.
(For both the Region and Pseudo layer)
Add the inregion formula to the other Pseudo layer
1 Select the second Pseudo layer in the algorithm.
The contents of its formula appear in the Formula dialog box, the default linear
ramp formula without the region statement. (This should be the layer containing
the ‘SE_photo’ dataset.)
2 On the Formula dialog, select Open from the File menu.
The Open Formula file chooser dialog opens. It is already set to the directory
containing both the original ‘linear_ramp.frm’ formula and your modified
‘linear_ramp_inregion.frm’ version.
3 Click on your ‘linear_ramp_inregion.frm’ formula, then click OK.
The formula is loaded and replaces the original linear ramp formula.
Your modified formula is now loaded into both Pseudo layers, so it will both
images.
4 Click Close on the Formula dialog to close it.
Display the images as red and green
1 Right-click on the ‘[Ps]:Pseudocolor’ surface icon, then select Red Green
Blue.
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The surface Color Mode changes to Red Green Blue.
2 Right-click on each of the Pseudo layers and change them to Red and
Green layers (as you did previously).
The two images display as red or green, but this time notice that the areas of
overlap (combined colors like yellow) are constrained to the areas where the
regions overlap. This is the effect of the shape of the regions and the use of the
‘inregion’ statement in the formula for each Pseudo layer.
Display the images as a greyscale mosaic again
1 Right-click on the ‘[RGB]:Pseudocolor’ icon, then select Pseudocolor.
The surface Color Mode changes to Pseudocolor.
2 Right-click on each of the raster layers (Red or Green ) and change them to
Pseudo layers:
The mosaic redisplays in greyscale again, then the regions display.
Zoom into the vertical seam and turn on feathering
1 On the Algorithm dialog, turn off the ‘Feather’ option
2 Right-click in the image window, then select Quick Zoom, then Zoom to
All Datasets.
The image zooms back out to the full extents of the mosaic.
3 Zoom into the vertical area of overlap below between the west and east
photos (a freeway runs through the center).
drag a zoom box
around overlap area
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Notice that a vertical seam is very apparent between the two photos, and there is a
slight misaligment of features as well. This is typical of airphoto mosaics due to
differences in the brightness of each photo and the difficulty with very precise
rectification of multiple images.
4 On the Algorithm dialog, turn on the ‘Feather’ option.
The zoomed area redisplays with a blending of the two images. What was
previously a very noticable seam is now blended and almost undetectable.
To achieve this, feathering creates a mathematical blend of the two images in the
horizontal direction:
100% of
image A
50/50 blend (average
value of images A & B)
100% of
image B
image B
image A
overlap area
5 Right-click in the image window, then select Quick Zoom, then Zoom to
All Datasets.
The image zooms back out to the full extents of the mosaic.
Delete the region layers in the algorithm
1 Delete both ‘Region Layer (Outline)’ layers by holding down the Ctrl key,
selecting both, and then clicking Cut
.
Enter a description for the final red band algorithm
1 In the Algorithm dialog, change the text in the Description field to read:
Final red band mosaic - balanced and feathered
This text now becomes a brief description for the entire algorithm.
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Save the final red band algorithm to disk
1 From the File menu (on the main menu), select Save As....
The Save As... file chooser dialog opens.
2 In the Files of Type: field, select ‘ER Mapper Algorithm (.alg)’
3 In the Save As: text field, type the following filename:
Final_red_bands_mosaic
This name denotes that it is the final mosaic of the red band images.
4 Click OK to save the algorithm.
Your final red band algorithm is now saved to an algorithm file on disk.
The next step is would be to create balanced and feathered algorithms for the green
and blue band images, then assemble them into a final RGB color mosaic.
Close the image window and Algorithm dialog
1 Close the image window by selecting Close from the File menu.
2 Click Close on the Algorithm dialog to close it.
Only the ER Mapper main menu should be open on the screen.
What you
learned
194
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Define a region polygon to constrain areas of overlap
•
Display images so that areas of overlap are evident
•
Use the the region as a mask in a formula
•
Use edge feathering to minimize seam lines between adjacent images
ER Mapper Workbook - Airphoto Mosaic Applications
10
Creating the final
mosaic
This chapter explains how to apply the same processing techniques to the green
and blue band data in each image, and assemble them into a final RGB color
mosaic. You will also learn about using an algorithm as a template to apply the
same processing to other bands or datasets.
Note: The information in this chapter is provided to give you an understanding of the
processes involved. You would normally use the Color Balancing Wizard to do
this automatically.
About algorithms as templates
Any algorithm can be used as a template to apply the same processing to other
datasets without having to repeat all the steps used to create the algorithm
originally. This can save you much time and trouble, and simplify what can
sometimes be rather complex processing to create large mosaics of airphotos. For
example, instead of repeating all the steps in the previous two chapters to color
balance and feather the green and blue band data, you will use the red band
algorithm you already created and simply adjust it where needed.
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Chapter 10#Creating the final mosaic#z Hands-on exercises
Using algorithms as datasets
Up until now, you have loaded raster datasets into your algorithms (actual image
files residing on disk). ER Mapper also lets you use an algorithm as input to
another algorithm, just as if the algorithm were actually a dataset. This feature lets
you perform processing in stages, without using the time and disk space of writing
a new dataset to disk at each stage.
For example, when you balanced and feathered the four red band images, you
saved it as an algorithm. This algorithm can be loaded into the red layer of another
RGB algorithm (as if it were a dataset), and ER Mapper will automatically process
all four of the image files as if they were merged into a single file.
Note: ER Mapper also has an extension of the algorithm concept called a Virtual Dataset
(or VDS). A Virtual Dataset is a special type of algorithm that can be used exactly
like a real dataset for the most part, but the virtual image is computed on demand.
(A VDS even has an ‘.ers’ file extension like a real dataset.) One common
application for a VDS is to link several files together (such as a mosaic) and
reference them as if they were one file. The difference between using an algorithm
and a Virtual Dataset is that you can calculate statistics for a VDS, define regions,
and several other things that you cannot do with an algorithm. See the ER Mapper
Tutorial and User Guide manuals for more information.
Hands-on exercises
These exercises show you how to apply the final balancing and feathering
processing to the green and blue bands in each image, and assemble them into a
final RGB color mosaic.
What you will
learn...
Before you
begin...
196
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Use an algorithm as a template to apply the same processing to other data
•
Create an RGB algorithm to display the final mosaic
•
Enhance the overall contrast of the final mosaic
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
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Chapter 10#Creating the final mosaic#z 1: Creating green and blue band mosaics
1: Creating green and blue band mosaics
Objectives
Learn how to use the red band algorithm as a template to create mosaics for the
green and blue bands of each image.
Open the final red band mosaic algorithm
1 On the main menu, select Open form the File menu.
An image window and the Open dialog appear.
2 From the Directories menu (on the Open dialog), select the path ending
with \examples.
3 Double-click to open the directory named ‘airphoto_training.’
4 Double-click on your ‘Final red_bands_mosaic.alg’ algorithm to open it.
The balanced greyscale mosaic of the red airphoto bands displays. Once you have
created an algorithm, you can use it as a template to easily apply the same
processing to other datasets or bands of data.
Display the green band (band 2) of each image
1 From the View menu, select Algorithm.
The Algorithm dialog opens.
2 Click on the green ‘[Ps]:Pseudocolor’ icon.
Process diagrams for both layers appear in the Layer panel.
3 In the process diagram for each layer, select B2:Green from the Band
Selection list.
1 - click surface icon
2 - select B2:Green
for both layers
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This tells ER Mapper to process the green band (band 2) of each image.
4 Click the 99% Contrast Enhancement
button.
The mosaic image redisplays, but this time shows the green band data for each
image in the mosaic. (The green band data is slightly brighter overall.)
Histogram match the green band of the airphotos
The 99% Contrast Enhancement
button has reset the transforms in both
layers to optimize the contrast of each green band image separate from the other.
Sometimes this produces acceptable results by itself to balance the contrast of all
images, but you should try histogram matching to see if you can get any
improvement.
1 Select the top layer containing the ‘San_Diego_Airphoto_34_rectified.ers’
dataset .
Only the process diagram for that layer displays. As with the red band data, this
will be the reference dataset to which the contrast of the other dataset will be
matched.
2 Click the Edit Transform Limits
button in the process diagram.
Edit Transform Limits button
The Transform dialog opens showing the histogram for the
‘San_Diego_Airphoto_34_rectified.ers’ dataset.
3 In the Transform dialog, click the Histogram match
button.
Histogram match button
4 If the dialog appears explaining the histogram match function, click Yes to
continue.
ER Mapper reprocesses the mosaic image and adjusts the contrast slightly so that
both images have similar contrast characteristics.
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Tip:
It is acceptable to use a different reference image for the green or blue histogram
match than for the red band. Typically, in larger mosaics, you would try other
images as the reference image to see if they produce better results. The idea is to
get the best overall contrast between all images, no matter what manner you
choose.
5 Click Close on the Transform dialog.
You have now performed exactly the same steps on the green band data as you did
earlier for the red band data. Each layer has a formula that processes only the data
inside the region polygons, and the linear ramp formula to balance the brightness
shifts across individual images.
Enter a description for the final green band algorithm
1 In the Algorithm dialog, change the text in the Description field to read:
Final green band mosaic - balanced and feathered
This text now becomes a brief description for the entire algorithm.
Save the final green band algorithm to disk
1 From the File menu (on the main menu), select Save As....
The Save As... file chooser dialog opens.
2 In the Files of Type: text field, select ‘ER Mapper Algorithm (.alg)’.
3 In the Save As: text field, type the following filename:
Final_green_bands_mosaic
This name denotes that it is the final mosaic of the green band images.
4 Click OK to save the algorithm.
Your final green band algorithm is now saved to an algorithm file on disk.
Display the blue band (band 3) of each image
1 From the View menu, select Algorithm.
The Algorithm dialog opens.
2 Click on the green ‘[Ps]:Pseudocolor’ icon.
Process diagrams for both layers appear in the Layer panel.
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3 In the process diagram for each layer, select B3:Blue from the Band
Selection list.
This tells ER Mapper to process the blue band (band 3) of each image.
4 Click the 99% Contrast Enhancement
button.
The mosaic image redisplays, but this time shows the blue band data for each
image in the mosaic.
Histogram match the blue band of the airphotos
The blue bands of airphotos often exhibit the most problem with contrast. These
photos are from the southern California area, which suffers from considerable air
pollution. The effects of this haze are most apparent by increased brightness and
blurring of ground features in the blue band image. (The blue wavelengths of light
are the shortest, so they are scattered more by small particles in atmospheric haze
than the green and red band images.) However, these color balancing techniques
work fairly well at minimizing the effect.
1 Select the second layer containing the
‘San_Diego_Airphoto_36_rectified.ers’ dataset .
Only the process diagram for that layer displays. As with the green band data, this
will be the reference dataset to which the contrast of the other dataset will be
matched.
2 Click the Edit Transform Limits
button in the process diagram.
Edit Transform Limits button
The Transform dialog opens showing the histogram for the
‘San_Diego_Airphoto_36_rectified.ers’ dataset.
3 In the Transform dialog, click the Histogram match
Histogram match button
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Chapter 10#Creating the final mosaic#z 2: Creating the final RGB algorithm
4 If the dialog appears explaining the histogram match function, click Yes to
continue.
ER Mapper reprocesses the mosaic image and adjusts the contrast slightly so that
all four images have similar contrast characteristics.
5 Click Close on the Transform dialog.
You have now performed exactly the same steps on the blue band data as you did
earlier for the red and green bands.
Enter a description for the final blue band algorithm
1 In the Algorithm dialog, change the text in the Description field to read:
Final blue band mosaic - balanced and feathered
This text now becomes a brief description for the entire algorithm.
Save the final blue band algorithm to disk
1 From the File menu (on the main menu), select Save As....
The Save As... file chooser dialog opens.
2 In the Files of Type: text field, select ‘ER Mapper Algorithm (.alg)’.
3 In the Save As: text field, type the following filename:
Final_blue_bands_mosaic
This name denotes that it is the final mosaic of the blue band images.
4 Click OK to save the algorithm.
Your final blue band algorithm is now saved to an algorithm file on disk.
2: Creating the final RGB algorithm
Objectives
Learn how to display the individual band mosaics as an RGB algorithm, and how
to adjust the final contrast and color.
Run the Image Display and Mosaic Wizard
ER Mapper lets you display an algorithm just as if it were a dataset. For example,
you will take the three algorithms you created earlier and display them as the red,
green and blue components of an RGB algorithm.
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1 On the main menu, click the Image Display and Mosaic Wizard
button.
The Image Wizard dialog opens.
2 On the Image Wizard dialog, click the
file chooser button.
3 From the Directories menu (on the Select File dialog), select the path
ending with the text \examples.
4 Double-click on the directory named ‘airphoto_training.’
5 From the Files of Type list, select ‘ER Mapper Algorithm (.alg)’.
The contents of the file list change to show files with ‘.alg’ extensions
(algorithms).
6 Double-click on the algorithm ‘Final_blue_bands_mosaic’ to load it.
7 Select the Display image in 2D and the Mosaic all files of this type
options.
This will cause the wizard to search for the same type of file in the
‘airphoto_training’ directory and to mosaic them into one image.
8 Click the Next > button on the Image Wizard dialog.
ER Mapper runs the wizard and creates a multi-layer Pseudocolor algorithm.
Display the final mosaic in RGB color
The Image Display and Mosaic wizard should have mosaiced all the similar
algorithms that it found in the ‘airphoto_training’ directory. This should be the
‘Final_blue_bands_mosaic’, ‘Final_green_bands_mosaic’ and
‘Final_red_bands_mosaic’ algorithms. It might also have included the original
‘red_bands_balanced_mosaic” algorithm, which is not wanted in our final RGB
image.
1 In the Algorithm dialog, if necessary, remove the unwanted
‘red_bands_balanced_mosaic’ layer by selecting it and clicking on the Cut
button.
The algorithm should now have three Pseudo layers in one Pseudocolor surface.
We must now change these to Red Green and Blue layers in an RGB surface.
2 Right-click on the ‘[Ps]:Pseudocolor’ surface icon, then select Red Green
Blue.
The surface Color Mode changes to Red Green Blue.
3 Right-click on each of the Pseudo layers and change them to Red, Green
and Blue layers.
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The image should now display in RGB color.
4 Click the 99% Contrast Enhancement
button.
The complete mosaic image displays in RGB. Notice that there still some minor
contrast and color differences between images, but overall the mosaic should look
fairly good.
Increase the overall contrast of the RGB mosaic
The initial mosaic of the red, green and blue band images often sacrifices overall
contrast to make sure the images are balanced relative to each other. Now you can
increase the contrast of the overall mosaic as desired.
1 Select the Red layer in the algorithm.
2 Click the right-hand Edit Transform Limits
diagram.
button in the process
The Transform dialog box opens showing the histogram for the entire red band
mosaic of four images.
3 In the Transform dialog, double-click on the Create autoclip transform
button.
Create autoclip transform button
The ER Mapper autoclip percentage dialog opens. This dialog lets you set
the amount of clip applied to the histogram. The default is 99%.
4 Enter the value 97 then click OK.
The transform line changes automatically to apply a 97% clip to the data. (97%
clips 3% off the histogram–1.5% from both the low and high ends.)
5 Click the Move to next green layer in surface
Transform dialog.
button on the
ER Mapper selects the Green layer and displays its histogram.
6 Click on the Create autoclip transform
button.
The 97% clip transform line is applied to the green layer histogram.
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7 Click the Move to next blue layer in surface
button.
ER Mapper selects the Blue layer and displays its histogram.
8 Click on the Create autoclip transform
button.
The 97% clip transform line is applied to the blue layer histogram.
Notice that the overall contrast is increased and adds more color to the mosaic
image.
9 If desired, try other autoclip percentages or the Histogram equalize or
Gaussian equalize options on all three layers and see the result.
You can easily fine tune the contrast of the entire mosaic until you get it just right.
10 When finished, reset each layer to a 97% autoclip transform.
Zoom in to crop off edges and blank areas
After creating a mosaic, it is often desirable to crop off uneven edges or zoom in to
make a map of only a portion of the overall mosaic area.
1 From the View menu, select Geoposition.
The Algorithm Geoposition Extents dialog opens.
2 Click the Extents tab to display the current mosaic extents.
3 Enter the following values in the Eastings and Northings Top Left and
Bottom Right fields:
Top Left - Easting: 483610
Top Left - Northing: 3623199
Bottom Right - Easting: 487199
Bottom Right - Northing: 3619609
edit values
(Enter/Return
to validate)
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4 Click the Apply button.
ER Mapper zooms to the exact extents you entered, which crop off the outer edges
of the mosaic image. You can define the image extents either by entering exact Lat/
Long or E/N values, or visually by dragging a zoom box over the desired area.
5 Click Close on the Algorithm Geoposition Extents dialog.
Enter a description for the final RGB algorithm
1 In the Algorithm dialog, change the text in the Description field to read:
Final RGB mosaic of red/green/blue band algorithms
This text now becomes a brief description for the entire algorithm.
Save the final RGB algorithm to disk
1 From the File menu (on the main menu), select Save As....
The Save As... file chooser dialog opens.
2 In the Files of Type: field, select ‘ER Mapper Algorithm (.alg)’.
3 In the Save As: text field, type the following filename:
Final_RGB_mosaic
4 Click OK to save the algorithm.
Your final RGB algorithm is now saved to an algorithm file on disk.
Close the image windows and Algorithm dialog
1 Close the image windows by selecting Close from the File menu.
2 Click Close on the Algorithm dialog to close it.
Only the ER Mapper main menu should be open on the screen.
What you
learned
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Use an algorithm as a template to apply the same processing to other data
•
Create an RGB algorithm to display the final mosaic
•
Enhance the overall contrast of the final mosaic
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11
Color balancing
image mosaics
This chapter explains how you use the ER Mapper Image Balancing Wizard
for Airphotos to balance and color match airphoto mosaics. The previous
chapters outlined how you would perform these tasks manually. This was to give
you an understanding of what is involved. You will now see how much easier it is
to use the Image Balancing Wizard for Airphotos to perform the same tasks
automatically.
Hands-on exercises
These exercises show you how to balance and color match mosaic algorithms
using the Image Balancing Wizard for Airphotos.
For these exercises, we will be using the airphoto mosaic algorithm we created
previously using the Image Display and Mosaic Wizard.
What you will
learn...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
•
Use the Image Balancing Wizard to balance and color match an airphoto mosaic.
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•
Before you
begin...
Compress and save the final image.
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
1: Color balancing the mosaic
Objectives
Learn how to use the Color Balancing Wizard for Airphotos to color
balance mosaiced images so that they interface seamlessly with one another.
Open the airphoto mosaic
1 On the main menu, click the Open
button.
click to open
algorithm
2 From the Directories menu, select the \examples path.
3 Open the ‘airphoto_training’ directory.
4 Double-click on the algorithm ’airphoto_mosaic.alg’ to open it.
This is the algorithm that you saved in a previous exercise. It comprises four
compressed airphotos of San Diego that were mosaiced using the Image Display
and Mosaic Wizard.
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Open the Image Balancing Wizard for Airphotos
1 Click on the Image Balancing Wizard for Airphotos
Common Functions toolbar to open the wizard.
button on the
The wizard processes the currently active image window
2 Select the Images have changed and need reanalyzing option.
The wizard only has to analyze the images the first time it is used on them, and
skips over it if the images have been previously analyzed. Selecting this option
forces the wizard to analyze the images regardless of whether this has been done
before.
3 Click on the Next> button to go to the next wizard page.
Analyze images for balancing
The wizard requires the images to be analyzed before it can do the balancing. The
analysis information is stored in the image dataset header files. If the images have
not yet been analyzed or you selected the reanalyzing option, the wizard will now
do so.
1 Click on the Next> button for the wizard to analyze the images.
The wizard will calculate the statistics for the four images and write the
information into their respective header files.
2 Click on the Next> button to go to the next wizard page.
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Select how to balance the images
In addition to color balancing, you also have a number of options for clipping the
image. These are described below:
210
Original
Remove any color balancing and display the
unbalanced images
Balanced
Display the balanced images but do not clip
edges.
Balanced
with no
black
edges
Display the balanced image(s) and remove the
black edges.
It is preferable not to select this option when
balancing images that have very dark water,
near the edges of the image. The color
balancing wizard for airphotos may select too
much of the image as dark edges to be
removed.
Balanced
with clip
regions
When mosaicing images, compute clip regions
to hide the edges between images. (The wizard
re-computes the clip regions every time you
run it.)
By default, the wizard turns feathering ON for
when balancing with clip regions, and OFF in
all other cases.
Show clip
regions as
a vector
overlay
Create a vector layer which outlines the clip
regions.
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Chapter 11#Color balancing image mosaics#z 1: Color balancing the mosaic
1 Select the Balanced with clip regions option.
2 Do not select the Correct for water areas because the image does not
have large areas of water.
3 Click on the Next> button for the wizard to balance the images and go to
the Color matching page.
The wizard will create the clip regions and then balance the image. It will then
display it in the image display window as the temp-balance algorithm.
Color matching the image
To create a seamless mosaic, the wizard is able to match the colors of the mosaiced
image to the whole mosaiced image or to one of the images that are part of the
mosaic. Alternatively you can skip the color matching altogether.
For this exercise we will match the color to the
‘San_Diego_Airphoto_39_compressed.ers’ image.
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1 Select the Select a single file to match colors to option, and then click on
the Next button.
2 Use the file chooser button to select the image to which the colors are
being matched. In this case we will select
‘San_Diego_Airphoto_39_compressed.ers’.
3 Select the Apply 99% clip option to improve the contrast, and click on the
Next button.
Caution: You would not select the Apply 99% clip option if you are going to compress the
image. You would not be able to reverse it when the image is decompressed.
The wizard will display the status of the color matching which can take some time
to finish. It will then display the final balanced and matched image in temporary
algorithm.
4 Click on the Finish button to exit the Color Balancing Wizard for Airphotos.
View the algorithm
1 On the main menu, click the Edit Algorithm
button.
The Algorithm dialog box opens.
You now have a algorithm that displays the Red, Green and Blue layers of the four
images.
2 Select the top Red layer and click on the Edit Formula
process diagram.
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button on the
Chapter 11#Color balancing image mosaics#z 1: Color balancing the mosaic
This will open the Formula Editor.
You should notice that the wizard has applied a formula to the layer. This is
displayed in the text box at the bottom of the Formula Editor dialog box.
The formula applies a balancing function, balance(), to the area of the image that
falls within the automatically created clip region, ‘Image Clip’. Areas outside the
clip region are converted to nulls.
3 On the Formula Editor dialog , click on the Red button to view the formula
for the next red layer.
Red button
Note that the formula applied is the same as that for the top red layer.
4 Click twice more on the Red button, to move to the two lower red layers.
Not that, in both cases, the formula applied is the same.
5 Repeat the above steps for the Green and Blue layers by clicking on the
Green and Blue buttons respectively.
Green button
Blue button
6 Click on the Close button to exit the Formula Editor.
7 Once again select the top Red layer, and click on the Edit Transform
Limits
button on the right side of the Process Diagram.
This will open the Transform dialog box.
8 View the transforms of all the Red layers by clicking on the Red
button.
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Notice that the wizard has matched the histograms of the four layers. The
following picture illustrates this.
Top layer
Second layer
Third layer
Fourth layer
9 Repeat the above for the Green and Blue layers.
In all cases note how the wizard has matched the histograms for the four images
that make up the mosaic.
Save the balanced algorithm to disk
1 From the File menu (on the main menu), select Save As....
The Save Algorithm file chooser dialog opens.
2 From the Directories menu, select the path ending with the text
\examples.
3 Double-click on the directory named ‘airphoto_training’ to open it.
4 In the Save As: text field, type the following filename:
airphoto_mosaic_balanced.alg
This name denotes that it contains a balanced mosaic of the airphoto images.
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5 Click OK to save the algorithm.
Your balanced algorithm is now saved to an algorithm file on disk.
Close the image window and Algorithm dialog
1 On the main menu, select Close from the File menu to close the image
window.
2 Click Close on the Algorithm dialog.
Only the ER Mapper main menu should be open on the screen.
What you
learned
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Use the Color Balancing Wizard for Airphotos to balance and color match the
mosaiced images.
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12
Composing maps
This chapter explains how to use ER Mapper’s Page Setup and Map Composition
tools to create top quality cartographic maps. You will learn about setting up a
page size, scale and extents for your map, how to draw vector annotation, how to
add map objects such as coordinate grids and scale bars, and considerations for
printing to hardcopy devices.
Note: The following exercise is a simplified example of creating a map. More details on
some aspects are provided at the end of the chapter, and you are referred to the ER
Mapper User Guide for more complete information.
About map composition
ER Mapper provides a complete set of map composition tools that let you easily
transform images into top quality image maps. Your maps can include common
map objects such as coordinate grids, scale bars, symbols, legends, north arrows,
and more. You can use the annotation tools to draw lines, text, shaded polygons,
and other vector objects. Your maps can also include other layers to add vector
data from GIS systems, tabular data, or other external data.
ER Mapper’s map composition also has an open design and is user-extendable.
You can add your own Postscript map objects to ER Mapper's map object library,
such as company logos or north arrows, include external text or graphic image
files, and many other types of data. You can also modify the default attributes of
map objects and save them under your own unique names for later use.
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The following diagram shows the general procedure for creating and printing a
map in ER Mapper:
Image
processing
Page
setup
Compose
map
Save
algorithm
Print
map
Create the desired image using algorithm
processing and any dynamic link vector
or tabular overlays to be included.
Specify page setup parameters for the algorithm
to define the position of the image on an output
page, map scale, margins, background color, etc.
Compose the map by dragging and dropping map
objects, specifying object attributes, and
drawing annotation such as lines and text.
Save the vector map composition file, then save
the algorithm containing the annotation/map
composition layer and raster layers.
Print the map on your hardcopy device, or
to an external file format (TIFF, CGM, etc.).
Hands-on exercises
These exercises give you practice setting up an algorithm to create a map, defining
Page Setup parameters, and composing the map by adding map objects and other
annotation.
What you will
learn...
218
After completing these exercises, you will know how to perform these tasks in
ER Mapper:
•
Define Page Setup parameters for an algorithm
•
Add an Annotation/Map Composition layer to an algorithm
•
Add a clip mask around the image
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Chapter 12#Composing maps#z 1: Setting up the page
Before you
begin...
•
Draw annotation objects (lines, text, polygons, etc.) on your map
•
Place map objects (grids, scale bars, etc.) on your map
•
Specify color and other attributes for annotation and map objects
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
1: Setting up the page
Objectives
Learn to use ER Mapper’s Page Setup options to define the position of an image
on an output page, and specify other options such as map scaling parameters and
background color. In this case, you will create a 1:24,000 scale map to be printed
on a large format hardcopy device.
Open the final RGB mosaic algorithm
1 On the main menu, click the Open
button.
An image window and the Open dialog box appear.
2 From the Directories menu, select the \examples path.
3 Open the ‘airphoto_training’ directory, then double-click on the algorithm
‘airphoto_mosaic_balanced.alg’ to open it.
This is the image mosaic image you created earlier, and you will use it to create
your map.
4 Re-size the image window so that the displayed image is a perfect
rectangle.
This will crop the image to remove the jagged edges.
Display the Annotation toolbar
1 On the main menu, select Annotation from the Toolbars menu.
ER Mapper adds a third toolbar with buttons for quick access to common functions
used for annotation and map composition.
Specify Metric or Imperial units for page setup
1 On the main menu, select Preferences from the Edit menu.
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The Preferences dialog opens providing General, Datasets, 3D Options,
and Advanced tab pages.
2 Select the General tab page (if needed), then select either Metric or
Imperial from the ‘Display Units’ drop-down list (whichever you prefer).
3 Click Close on the Preferences dialog to close it.
All values regarding the plot size, margin sizes and other page setup parameters
will be displayed in the measurement units you selected.
Open the Page Setup dialog box
1 From the File menu, select Page Setup (or click the Setup Algorithm
Page Size
button on the Annotation toolbar).
The Page Setup dialog box opens. This dialog provides controls for you to
choose a default hardcopy device, position and scale your image on the output plot
area, specify a background color and more.
apply settings
to current
algorithm
number of pages
hardcopy device
will print using
current settings
page contents
outline (blue box)
page extents
outline (red box)
select default
hardcopy device
overall size
of page extents
(plot size)
select predefined
plot sizes
size of borders
surrounding
page contents
e xact
m ap sca le
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Note: You can also use the Page Setup Wizard to set the page up. This will not be
described in this exercise. Refer to the ER Mapper User Guide for information on
the Page Setup Wizard.
The area on the left side shows the size and shape of the plot in red (the “page
extents”), and the relative size and position of the algorithm image within the plot
area in blue (the “contents extents”).
Select the destination hardcopy device
1 Select the ‘Hardcopy Control Files’ option at the top (if it is present).
This tells ER Mapper to use its own set of device drivers. (If you are running
ER Mapper on a PC, you can also choose to use the Windows drivers.)
2 Click the Default Hardcopy
file chooser button.
The Default Hardcopy dialog opens to let you select the type of printer or
graphics file that you will be using.
3 From the Directories menu, select the \hardcopy path.
A list of directories for categories of hardcopy devices and file formats displays.
4 Double-click on the directory named ‘HP’ to open it and view a list of
available options for Hewlett-Packard printers.
5 Double-click on the entry ‘HP_DesignJet_300dpi_A0.hc’ to select it.
This device is now selected as your default hardcopy device, and we will assume
that your example map will be printed on it. It is a good idea to choose the device
you intend to print on so you can see how large your plot will be later. However,
you can change and print to any other device or file format at print time.
(The HP DesignJet is a large format color inkjet plotter. The entry you selected is
designed to tell the printer to print at 300 dots per inch on an A0 size area (35
inches or 89 cm wide), which the device’s total printable area.
Specify how the page or map contents can be scaled
The Constraints drop-down list lets you specify how map objects are scaled
relative to the output page. Typically you need to decide which parameters are
most important for your map: a fixed page size, fixed borders, or a fixed map scale.
1 From the Constraints drop-down list, select Auto Vary:Page.
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The outlines representing the page extents (red) and page contents (in blue)
become the same size and shift down to the center of the white area on the Page
Setup dialog. The Border and Scale fields are now editable.
Auto Vary:Page mode tells ER Mapper that it can automatically change the size
of the image extents (size) to accommodate any changes you make to the map
scale or the size of borders surrounding the image. (Other Constraints options
will automatically change plot borders or map scale if other parameters are
changed.)
2 Click on the Snapshot current image window extents button.
This will crop the page contents extents with to that with which it is currently
being displayed. The page will still display the whole image, and will require a
clip-mask to remove the edges.
Specify the output map scale
1 In the Scale - 1: text field, enter the value 12000 then press Enter or
Return to validate.
ER Mapper sets the size of the page contents (the physical size of the image on the
page) to print at 1:12,000 map scale.
Specify borders surrounding the page contents
Right now the page extents and page contents are the same size. Next you will add
borders around the contents (the seismic image) so you have space to add a title,
scale bar, map grid, and other items.
1 In the text fields under ‘Border,’ enter the following values for each field in
the units you are using (press Enter or Return after each to validate):
Top: 2.0 (inches) or 50 (mm)
Left: 2.0 (inches) or 50 (mm)
Right: 2.0 (inches) or 50 (mm)
Bottom: 4.0 (inches) or 100 (mm)
By adding borders, you increased the total plot size to approximately 420 by 629
mm (or about 29 by 28 inches). The blue outline shows the relative size and
position of the page contents in the new, larger plot size. The physical size of the
mosaic image (page contents) has not changed, it will still print at 1:12,000 scale.
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Tip:
After setting the desired map scale and border values, notice that the Hardcopy
Pages Across and Down fields show the percentage of device’s A0 size print area
that the plot will occupy (45% of the width of an A0 page in this case). If your total
plot size (page extents) is larger than the print area of your device, these values
will be greater than one, indicating that ER Mapper would divide the plot and print
each portion on a separate page or strip.
Set the background color to white
1 Select the text in the Background Color field, type white, and press
Enter or Return to validate.
ER Mapper sets the page background color to white (the areas of the page
surrounding the page contents). If you will be printing on a device that has a white
background, it is often helpful to set the background color to white while you are
composing the map to get a better idea of the final output. (You can use the Set
Color button as well to choose any arbitrary background color.)
Your Page Setup dialog should now look like this (units shown are Metric):
percentage of A1 size
area the plot will fill
size of page contents
(image) relative to
total size and shape
of plot (page extents)
total size of plot
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Save the algorithm with the Page Setup parameters
1 Click OK on the Page Setup dialog to close it.
ER Mapper redisplays the colordrape image to show the white page border areas
that you added in Page Setup.
Note: The edges of the airphotos are still visible until you add a clip mask to the image to
mask them out. You will do this next.
2 From the File menu, select Save As... to save the algorithm under your
own name.
3 From the Directories menu, select the \examples path.
4 Double-click on the directory ‘airphoto_training’ to open it.
5 In the Save As: text field, enter the text Final_mosaic_map.
6 Click OK to save the algorithm, which now includes your page setup
parameters.
2: Adding a clip mask around the image
Objectives
Learn to add a clip mask map object to an image to block out any undesired areas.
Add a vector layer for the clip mask
1 On the Common Functions toolbar, click the Annotate Vector Layer
button.
Annotate Vector Layer
button
The New Map Composition dialog box opens to ask what type of annotation
you want to create.
2 Make sure the Vector File option is selected, then click OK on the New
Map Composition dialog.
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ER Mapper opens the Tools dialog containing your drawing tools. Move the
Tools dialog next to the right side of your image.
Add a clip mask map object
1 On the Tools dialog, click on the Map Rectangle
button.
The Map Object Select and Map Object Attributes dialogs open. These
dialogs let you drag-and-drop map objects onto your page and specify color, text
style, and other attributes.
2 In the Map Object Select dialog, select Clip Mask from the Category
drop-down list.
Previews of the two types of clip mask objects appear. One masks out areas inside
the mask border, and the other masks areas outside the border. (The name of the
object is shown in the status line at the bottom of the dialog when you point to it.)
3 Point to the icon titled Clip_Mask/Outside (the green border outside the
image), then drag and drop it into the map algorithm image window.
drag and drop object
onto map page (image
window)
The clip mask object is “dropped” onto the page and appears as a small box in the
center with four selection handles. (You will learn more about bounding boxes
later.)
4 In the Map Object Attributes dialog, click the Fit Grid button.
The bounding box automatically expands to cover the exact area that wish to
display (the extents you defined in the Page Setup dialog earlier).
5 In the Map Object Attributes dialog, turn off the ‘Fast Preview’ option.
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The clip mask map object draws over the image. Now the exact area you wish to
plot as your map is bounded by the white borders area.
Turn off Fast Preview
to view mask object
Fit Grid to fit box
to zoom extents
Save the clip mask as a separate annotation file
1 On the Tools dialog, click the blue Save As
button.
The Map Composition Save As dialog opens.
2 Make sure the ‘Vector File’ option is selected, then click the
next to ‘Save to File.’
button
3 From the Directories menu (on the file chooser dialog) , select the
\examples path.
4 Double-click on the directory ‘airphoto_training’ to open it.
5 In the Save As: text field, type the text map_clip_mask.
6 Click OK to validate the filename.
7 Click OK on the Map Composition Save As dialog.
Your clip mask vector annotation object are saved to an ER Mapper format vector
file (.erv) on disk.
8 Click Close on the Tools dialog.
Label the annotation layer
1 Click the Edit Algorithm
button on the main menu.
On the Algorithm dialog, notice that ER Mapper has added an ‘Annotation
Layer’ to the algorithm layer list to display the vector clip mask you created.
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2 Change the annotation layer’s label to clip mask.
3 Click Close on the Algorithm dialog to close it.
3: Drawing vector annotation
Objectives
Learn to use the vector annotation tools to draw text, lines and polygons, and the
change the color, style and other attributes of the objects.
Zoom to the Page Contents and Page Extents
Currently the image is zoomed out to show the page extents and the relative
position of the image within it.
1 Expand the image window size to make it slightly larger.
2 Right-click on the image and, from the Quick Zoom menu, select Zoom to
Page Contents.
The image zooms in to the extents of the page contents (the extents of the mosaic
image that you wish to appear in your map). Since you will draw annotation on the
image, it is helpful to maximize the area on the screen used for the image. Later
you will zoom to the extents again to add map objects in the border areas.
Add a second vector layer for map annotation
1 On the Common Functions toolbar, click the Annotate Vector Layer
button.
The Open Map Composition dialog box opens. Since your algorithm already
has one vector layer, you are prompted to reopen that dataset or create a new one.
2 Click New on the Open Map Composition dialog.
The New Map Composition dialog box opens.
3 Make sure the Vector File option is selected, then click OK on the New
Map Composition dialog.
ER Mapper opens the Tools dialog containing your drawing tools. Move the
Tools dialog next to the right side of your image.
Draw a polyline to trace the highway in the image
This image shows a highway running from the left center down to the lower right.
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1 On the Tools dialog, click once on the Polyline
button.
2 Draw a line to trace the highway path by clicking once at each point, then
double-clicking to end the line.
A line appears on your image to highlight the linear feature. Note that markers
appear on the line at each node to indicate that the line is “selected.”
View and modify the attributes of the polyline
1 On the Tools dialog, double-click on the Polyline
button.
The Line Style dialog box opens to let you choose attributes for your polylines.
2 Click the Set Color button, choose a bright blue color, then click OK to
close the Color chooser dialog.
The line color on the image changes to your selected color.
3 Click the Width drop-down list and choose 5.0 to increase the line width.
The attributes for your selected polyline change interactively.
4 On the Tools dialog, click on the Edit Object Extents
button.
The Map Composition Extents dialog opens to show information about the
polyline object. It shows the line length in map units, and other attributes such as
the number of vertices, geographic extents, and so on.
5 Click Close on the Map Composition Extents dialog.
6 On the Tools dialog, click the Select/Edit Points Mode
button.
7 Drag any node of the selected polyline to move it.
When a polyline is selected and Select/Edit Points Mode
is active, you
can reshape the line as desired by dragging the line nodes. (You will learn how to
move entire objects later.)
8 In the Line Style dialog, turn on the ‘Curved’ option.
ER Mapper applies a spline function to the selected line and reshapes it into
smooth, rounded curves. This can be helpful to create more visually pleasing lines
when tracing roads, rivers, and other curving linear features.
9 Turn off the ‘Curved’ option.
The line returns to its original appearance with straight segments at each node.
10 Click Close on the Line Style dialog.
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Tip:
To trace a long linear feature in a large image (such as this one), it is helpful to
draw the line along the entire extent of the feature first, then zoom into each area
and adjust the exact position of the vector object by moving the line nodes.
Draw a shaded polygon around a feature
1 On the Tools dialog, click on the Polygon
button.
2 Draw a polygon around any areal feature (such as a housing development)
by clicking once at each point, then double-clicking to close the polygon.
The polygon object appears surrounding the area, and it is selected. By default,
your polygon displays the currently selected line color, thickness, etc.
3 On the Tools dialog, double-click on the Polygon
button.
The Line Style dialog box opens to let your set polygon attributes. (The same
dialog is used for polylines, rectangles, and other vector objects.)
4 Click the Set Color button, choose a yellow color, then click OK to close
the Color chooser dialog.
5 Under Fill Pattern, click on one of the diagonal line fill patterns.
The pattern you choose appears in the Current Fill window on the dialog. The
polygon is filled with a diagonal yellow shade pattern.
6 On the Tools dialog, click on the Edit Object Extents
button.
The Map Composition Extents dialog opens to show information about the
polygon object, including the perimeter length and area.
7 Click Close on the Map Composition Extents dialog to close it.
Tip:
To delete a node from an existing polyline or polygon, use Select/Edit Points
Mode
to select it, click on the node to delete, then click the Delete Point
button. To add a node, click the Add Points Mode
on the line to add a node at that point.
button, then click
Draw a shaded oval and move and resize it
1 On the Tools dialog, click the Oval
button.
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2 Point anywhere inside the image, drag an oval shape and release.
A shaded yellow oval appears. By default, the oval is selected.
3 Under Fill Pattern, click on the top entry (clear or none).
The fill pattern is removed from the oval.
4 Click Close on the Line Style dialog.
5 On the Tools dialog, click the Select and Move/Resize Mode
button.
Select and Move/Resize Mode lets you move and/or resize the selected
object. Notice that the oval’s selection handles change–now there are eight
handles.
object handles–drag to resize
object as desired
6 Drag one of the selection handles to increase the oval size.
7 Point inside the oval, and drag it to a new location.
When an object is selected and Select and Move/Resize Mode
you can move the object by dragging it from inside.
8 In the Tools dialog, click the Delete Object
is active,
button.
The selected oval object disappears from the image. Selecting an object and
clicking Delete Object
Tip:
is the way to delete any vector annotation object.
If you delete an object by mistake, immediately click the Undo Last Delete
button to restore it.
Tips for selecting objects
ER Mapper’s annotation tool set provides two “select” tools for different tasks:
•
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Use the Select/Edit Points Mode
button to select a polyline or polygon
object when you want to move the individual line nodes, or select nodes.
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•
Use the Select and Move/Resize Mode
button to select any annotation
object when you want to move the entire object (drag from the center) or resize the
entire object (drag one of the yellow handles).
•
To select multiple objects at once, choose the Select and Move/Resize Mode
button. Then either drag a marquee box around all the objects, or select them
one at a time by holding down the Shift key and clicking on them.
Tip:
To duplicate an object, select it and click the Clone Object
button. This can
useful, for example, for copying blocks of text or creating exact copies of
polygons, ovals, and so on.
Draw and modify a text string
1 On the Tools dialog, click the Text Object
button.
The Text Style dialog box opens.
2 Drag a box inside the image about one-half inch in height.
3 In the Text Style dialog, click in the Text field at the bottom to position the
cursor, then type main highway.
The text appears on the image as you type.
4 In the Text Style dialog box, select the following text attributes:
Size: 72.0
Color: choose any bright color
Font Type: Postscript Stroke
Font: Helvetica-Bold
Notice that the text object automatically updates as you change the attributes.
Tip:
Text drawn as annotation can be set to always print at an exact point size (the
Fixed Text option on), or to automatically scale up or down proportionally at
whatever size the image is printed (Fixed Text option off).
5 Click the Select and Move/Resize Mode
button, then drag the text in
the image to overlap with the blue vector you traced earlier.
6 From the Angle (deg) drop-down list, select 310.0.
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The text string rotates 310 degrees counter-clockwise, so it now points down
toward the lower right. (You can also type any arbitrary rotation value. Text strings
rotate around their origin in the upper-left corner.)
7 On the Tools dialog, click the Select and Move/Resize Mode
button.
8 Point to the text block, and drag it to any desired position.
9 Click Close on the Text Style dialog to close it.
Place a highway number symbol on the road object
1 On the Tools dialog, click on the Map Polygon
button.
The Map Object Select and Map Object Attributes dialogs open.
2 In the Map Object Select dialog, drag and drop the Road_Maps/
Highway4 object onto highway line on the image.
The highway road symbol appears on the image.
3 In the Map Object Attributes dialog, set the following value (press Enter
or Return afterward):
Highway: 405
Fill Color: red
The highway number and color change.
4 On the Tools dialog, click the Select and Move/Resize Mode
button.
5 Resize and position the highway symbol as desired.
Tip:
ER Mapper contains a wide variety of special symbols you can use in maps. These
are located on the Map Objects dialog under Map_Symbols, Symbols, and other
categories.
Save the vector objects to an annotation file
1 On the Tools dialog, click the blue Save As
button.
The Map Composition Save As dialog opens.
2 Make sure the ‘Vector File’ option is selected, then click the
next to ‘Save to File.’
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3 From the Directories menu (on the file chooser dialog) , select the
\examples path.
4 Double-click on the directory ‘airphoto_training’ to open it.
5 In the Save As: text field, type the filename vector_annotation.
6 Click OK to validate the filename.
7 Click OK on the Map Composition Save As dialog.
Your vector annotation objects are saved to an ER Mapper format vector file.
8 Click Close on the Tools dialog.
Label the annotation layer
1 Click the View Algorithm for Image Window
menu.
button on the main
Notice that ER Mapper has added a second ‘Annotation Layer’ to the algorithm
layer list to display the interpretations you create.
2 Change the annotation layer’s label to interpretations.
Note: Clip masks will cover other vector annotation if they are above the other layers in
the algorithm layer list. (The same priority rule that applies to overlap in multiple
raster layers.) It is recommended that layers for clip masks be positioned below
other vector layers unless you want to mask other vector data.
3 Click Close on the Algorithm dialog to close it.
4: Defining map objects
Objectives
Learn to use ER Mapper’s Map Composition tools to place and modify map
objects such as scale bars, coordinate grids, north arrows, and others.
Zoom to the Page Extents to view the entire map page
1 On the Annotation toolbar, click the Zoom to Page Extents
button.
The image zooms out to the extents of the page defined for the algorithm, and
shows the white border areas where you will place map objects.
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2 On the Tools dialog, click on the Map Rectangle
button.
The Map Object Select and Map Object Attributes dialog boxes open on the
right side of the screen. These dialog boxes let you drag and drop map objects onto
the page in your image window, and specify attributes for the objects.
Layout the types and positions of map objects
Before creating your map, it is a good idea to determine which types of map
objects you want to use, and their relative sizes and positions on the page. In this
exercise, you will create a map with the following objects similar to this one
Map title
E/N grid
& labels
North
arrow
Company
logo
Scale bar
You will define these objects on your image window “page” in two ways:
234
•
draw a bounding box and drag-and-drop the object into it; or
•
drag-and-drop the object onto the page and resize the bounding box afterward
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Refer back to the diagram above as a guide for the size and position of map objects
you are asked to create in the next sections.
Add a third vector layer for cartographic symbols
1 On the Annotation toolbar, click the Annotate Vectors/Map Composition
button.
The Open Map Composition dialog box opens showing the names of the two
annotation files you created. You want to create a third new one.
2 Click New on the Open Map Composition dialog.
3 On the New Map Composition dialog that opens, make sure the Vector
File option is selected, then click OK.
ER Mapper opens the Tools dialog containing your drawing tools.
Add a main title above the image
1 On the Tools dialog, click on the Map Rectangle
button.
The Map Object Select and Map Object Attributes dialogs open.
2 Drag a bounding box centered at the top of the image window (leave some
space below it for grid labels).
drag a box above
the image
3 In the Map Object Select dialog, select Title from the Category
drop-down list.
4 Point to the icon titled Title/Scaling, drag it into the Map Object Attributes
dialog.
(The default title color is white so it does not appear initially.)
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5 On the Map Object Attributes dialog, change the following text and
attributes for your title:
Title: Airphoto Mosaic, San Diego (press Enter or Return afterward)
Font Color: black (either type or use Set Color button)
The title object automatically updates as you change the attributes.
6 On the Tools dialog, click the Select and Move/Resize Mode
button.
7 Resize (by dragging a handle) or reposition the title as desired.
The title text changes size automatically to fill at least one dimension of your
bounding box.
Tip:
If the title text is not visible, you can click on the Refresh Image
Tools dialog to force ER Mapper to re-display the image.
button on the
Add a scale bar below the image
1 In the Map Object Select dialog, select Scale Bar from the Category
drop-down list.
Previews of the various types of scale bar objects appear.
2 Point to the icon titled Scale_Bar/Box, then drag and drop it into a position
below the image.
The scale bar object is “dropped” onto the page and it draws a few seconds later.
The default attributes for the scale bar appear in the Map Object Attributes
dialog box.
Zoom in on the scale bar and change the attributes
1 On the Tools dialog, click the ZoomBox Mode
button.
2 Inside the image window, drag a box around the scale bar object to zoom in
on it.
3 On the Map Object Attributes dialog, change the following attributes for
your scale bar:
Labels Color: black
Labels Font: Helvetica-Bold (select from pop-up fonts dialog)
Units Font: Helvetica-Bold
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Notice that the scale bar object automatically updates as you change the attributes.
4 On the Annotation toolbar (on the main menu), dialog, click the Previous
Zoom
button.
ER Mapper zooms out to the previous zoom level (the page extents).
5 On the Tools dialog, click the Select and Move/Resize Mode
button.
6 Drag your scale bar object into the desired position, or resize it by dragging
one of the selection handles.
If you resize the scale bar (make it wider or narrower), ER Mapper automatically
adjusts the scale and divisions (it is a “smart” map object).
Tip:
To resize or move any map object, select it first using the Select and Move/
Resize Mode
button, then move or resize it as desired.
Add a north arrow on the lower-right
1 In the Map Object Select dialog, select North Arrow from the Category
drop-down list.
A list of icons representing various types of north arrows appears.
2 Point to the compass north arrow (North_Arrow/Compass), and drag it to
a position in the lower-right of the page.
The north arrow object drops onto the page.
3 Click the Select and Move/Resize Mode
button (on the Tools dialog),
and resize and position the north arrow as desired.
Tip:
ER Mapper’s north arrows are “smart” and will always point to north on a rectified
image.
Add a company logo on the lower-left
1 In the Map Object Select dialog, select Logo from the Category
drop-down list.
A list of icons showing some sample company logos appears.
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2 Point to the ER Mapper logo icon, and drag-and-drop it onto the lower-left
part of the page.
The logo object drops onto the page. Resize and position it as desired.
Tip:
You can add your own company logos as Postscript files and access them from the
standard Logos category used here.
Define an Eastings/Northings coordinate grid over the image
1 In the Map Object Select dialog, select Grid from the Category
drop-down list.
2 Point to the Grid/EN icon, and drag it into the image window.
The grid map object draws in the lower-right part of the image.
3 On the Map Object Attributes dialog, click the Fit Grid button.
ER Mapper automatically fits the bounding box exactly to the extents of the page
contents (image) on the page.
4 On the Map Object Attributes dialog, turn on the Fast Preview option.
Fast Preview tells ER Mapper not to update the object interactively as you
change the attributes.
5 On the Map Object Attributes dialog, change the following attributes for
your grid (use defaults for all others):
Grid Style: Full Grid
Border Type: Checks
Grid Spacing X: 500 meters
Grid Spacing Y: 500 meters
Top labels orientation: Horizontal Right
Tip:
You could have used the grid to clip the image without having a separate clip
mask. To do this you would select the Clip option.
6 On the Map Object Attributes dialog, turn off the Fast Preview option.
The grid map object is rendered using the attributes you defined. The grid spacing
is 500 meters, and the “checks” option puts a map collar around the image.
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Tip:
The Fast Preview option is very useful for working with complex map objects
that take time to redraw (such as a grid or algorithm image). This lets you change
all the attributes you desire or fine tune object size/position without ER Mapper
trying to update the object on the screen each time.
Adjust the size or position of any object
If desired, you can easily resize or position any map object by moving or resizing
the bounding box that contains it.
1 In the Tools palette dialog, click the Select and Move/Resize Mode
button.
2 Click on any map object to select it (the handles will appear), and drag the
bounding box to reposition it or change the size by dragging a handle.
Save the map composition file to disk
1 On the Tools dialog, click the blue Save As
button.
The Map Composition Save As dialog opens.
2 Make sure the ‘Vector File’ option is selected, then click the
next to ‘Save to File.’
button
3 From the Directories menu (on the file chooser dialog) , select the
\examples path.
4 Double-click on the directory ‘airphoto_training’ to open it.
5 In the Save As: text field, type the text map_composition.
6 Click OK to validate the filename.
7 Click OK on the Map Composition Save As dialog.
Your map objects are saved to an ER Mapper format vector file (.erv) on disk.
8 Click Close on the Tools dialog.
Note: When you close the Tools dialog (exit edit mode), ER Mapper redisplays the
image exactly as it will look when printed. (During edit mode, line thickness is
slightly exaggerated to help editing and modifications.)
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Label the map composition layer
1 Click the View Algorithm for Image Window
menu.
button on the main
On the Algorithm dialog, you now have three annotation layers–your new map
objects layer, your ‘vector annotation’ layer, and your ‘clip mask’ layer.
2 Change the ‘Annotation Layer’ label to map composition.
3 Click Close on the Algorithm dialog to close it.
Tip:
It is often helpful to separate different types of annotation into separate files as you
did here–one for a clip mask, one for vector drawing, and another for map objects.
This makes it easier to work with the data, and you can simply turn the desired
vector layers on/off to display/not display those items in your algorithm. (You
could have saved all your vector interpretations and map objects in the same file.)
Save the algorithm to update the changes
1 On the main menu, click the Save
toolbar button.
2 When asked to confirm the overwrite, click OK.
Your algorithm can now be printed using the Print
selecting Print from the File menu.
toolbar button or by
Note: It is important to remember to save your algorithm after defining map objects.
Otherwise the annotation layers and files will not be part of the algorithm when
you go to print it later.
Close all image windows and dialog boxes
1 Close the image window using the window system controls or by selecting
Close from the File menu.
Only the ER Mapper main menu should be open on the screen.
What you
learned...
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
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Define Page Setup parameters for an algorithm
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•
Add an Annotation/Map Composition layer to an algorithm
•
Add a clip mask around the image
•
Draw annotation objects (lines, text, polygons, etc.) on your map
•
Place map objects (grids, scale bars, etc.) on your map
•
Specify color and other attributes for annotation and map objects
Additional features of Map Composition
The preceding simple example covered only the basics of using ER Mapper’s Map
Composition, and following are some additional features. Refer to the chapter on
creating maps in the ER Mapper User Guide for complete information.
•
If you drag an object into a bounding box that already contains an object, the old
object is replaced by the new one. This is an easy way to try several north arrows,
for example.
•
Objects that are dragged and dropped to replace a current object automatically
inherit any common attributes from the previous object. For example, if you have a
red north arrow in a bounding box and then drag in a scale bar object, the scale bar
automatically inherits the red color (since both objects have the “Color” attribute in
common).
•
You can modify the default attributes of map objects and save them under your own
names (using Save As on the Map Object Attributes dialog).
•
You can draw other image processing algorithms you’ve created as map objects on
the page (using the Category: Algorithm on the Map Object Select dialog).
This is useful for drawing inset images that show an overview map, inset image, or
other types of processing techniques or data of the same area.
•
You can plot objects from external files like TIFF, EPS, or Targa (using the
Category: Image on the Map Object Select dialog)
•
You can import text directly from ASCII text files and plot it on your map page
(using the Category: Text on the Map Object Select dialog)
Page Relative and Map Unit Relative map objects
The vector map objects you defined in this exercise have their position and size
specified relative to the page, rather than to map units (such as Latitude
Longitude). This allows you to create standard map sheets with objects that remain
in a fixed size and position on the page, regardless of how the page is scaled or the
extents of the datasets used in the page contents are changed.
You can also specify the position of map objects in geographic coordinate units.
The position of each object is tied to a particular geographic location and map
sheet size.
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To specify a map object as map unit relative, turn off the Page Relative option
on the Map Object Attribute dialog box. The page relative attribute can be
assigned either before or after the object is dragged-and-dropped onto the page.
See the ER Mapper User Guide for more information.
Page Setup Constraints options
In the previous simple example, you chose the ‘Auto Vary:Page’ option, although
you could have chosen others as well. The Constraints options you can use are
summarized briefly below:
•
Fixed Page:Extents from Zoom–This is the default setting for all new algorithms,
where the contents scale and borders are taken from the current zoom extents of the
algorithm. For map making purposes, Extents from Zoom is not recommended
because it can effect line thickness and text sizing.
•
Auto Vary:Page–This mode allows ER Mapper to automatically vary the page size
to account for any changes made to the map scale or page borders. This mode is
easiest, for example, to print a map at an exact scale without regards to constraining
it to a specific page size. If you want to place map objects outside the image (page
contents) area, enter the desired border sizes to create space for them. (This is a
good initial choice when you are prompted to change the mode when using the
annotation tools.)
•
Auto Vary:Borders–This mode allows ER Mapper to automatically vary the page
borders to account for any changes made to the map scale or page size. This mode
is most useful for printing at both an exact map scale and exact plot size.
•
Auto Vary:Scale–This mode allows ER Mapper to automatically vary the map
scale to account for any changes made to the page size or page borders. This mode
is useful, for example, for printing an image at various sizes when exact map scale
is not important.
Printing your map
When you want to print your final map algorithm (using File/Print or the Print
button), ER Mapper asks for the name of the algorithm. When the print
operation begins, ER Mapper automatically locates, processes and renders all the
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datasets used in the algorithm into one final print image. In this case, your map
algorithm uses seven datasets–a mosaic of four airphotos, and three vector datasets
for clip mask, annotation and map items (which you created).
mosaic of
airphotos
printer
Mosaic Map
algorithm
map comp
dataset(s)
or
file (TIFF,
CGM, etc)
Since the map algorithm is made of several layers (and datasets), you can easily
change it. For example, to print the image without the map annotation, simply turn
off that layer in the algorithm, resave it, and print it.
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13
Compressing
images
This chapter shows you how to save your large mosaic as a compressed image.
About ECW compression
ER Mapper compresses images using wavelet compression technology which
offers very high quality results at high compression rates. You can typically
compress a color image to less than 2% to 5% of its original size (50:1 to 20:1
compression ratio) and compress a grayscale image to less than 5% to 10% of its
original size (20:1 to 10:1 compression ratio).
This means that, at 20:1 compression, 10GB of color imagery will compress down
to 500MB, which is small enough to fit on to a single CD-ROM. You may actually
achieve higher compression rates where your source image has a structure well
suited to compression.
In addition to reducing storage requirements, you can also use the free imagery
plug-ins for GIS and office applications to read the compressed imagery in a wide
range of software applications such as ArcView®, AutoCAD MAP®, MapInfo®,
ER Viewer, Photoshop™, Microsoft Office® and Excel®, and other software
applications.
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Saving a compressed image to disk
Objectives
Learn how to save large images in compressed format using the ER Mapper ECW
compression.
1 From the main ER Mapper File menu, select Save as a Compressed
Image.
The Compression Wizard will open.
Input image to be compressed
1 Select the Select input image (or mosaic) to compress option as the
source of the image(s) to be compressed and click on the Next > button.
2 In the Input file: field, click the Select File
button.
3 From the Directories menu, select the \examples path.
4 Open the ‘airphoto_training’ directory, then double-click on the algorithm
‘final_mosaic_map.alg’ to select it.
This is the image mosaic map that you created earlier, and you now save it as a
compressed image.
In addition to using an algorithm as the source image to be compressed, you could
specify any other file format supported by ER Mapper, such as ESRI BIL, TIFF,
JPG as the input.
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Compressed image file name
5 In the Output file: field, click the Select File
button.
6 From the Directories menu, select the \examples path.
7 In the Select File dialog, choose ER Mapper compressed images (.ecw) in
the Files of Type field.
8 Open the ‘airphoto_training’ directory.
9 In the Open: text field, enter the text final_mosaic_map_compressed
and separate each word with an underscore (_).
10 Click OK on the Select File dialog.
Your file name appears as the Output File name with a ‘.ecw’ extension.
ER Mapper will save the compressed image as a header (.ers) and a compressed
data (.ecw) file. You can use File / Open or one of the wizards to open the header
(.ers) or data (.ecw) file just like any other image file supported by ER Mapper.
Note: The data (.ecw) file contains embedded georeferencing information, so the header
(.ers) file can be dispensed with if the compressed image is to be used in
applications other than ER Mapper.
Compress to Grayscale, RGB or Multi
11 In the Compress to: field, select the Color (RGB) option
The compression engine internally converts the RGB color image into YUV color
space, specifically the one defined as the "JPEG Digital version of YUV". YUV is
a color space that separates out intensity (Y) from chromatic or color changes (U
and V). This enables more efficient compression of color imagery, ensuring that
detail is preserved. The RGB to YUV conversion (and back again for
decompression) is automatic; the user always sees the file as a RGB file.
Other compression options available are:
Grayscale
The compression engine constructs and compresses a
grayscale view of your input image data using the
normal formula for Intensity from Red, Green and Blue.
Multiband
The compression engine compresses all the bands of a
multi-band image. Use this option for compressing
hyperspectral images.
12 Click on the Next > button to continue
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Compression ratio
13 Check the Compress for Internet usage box.
This option is for compressed images to be served on an ER Mapper Internet Web
Server (IWS). The transfer rate over a network for images compressed with this
option is higher, thus allowing faster zooming and roaming. However, the actual
compression ratio achieved will be less than that for images compressed without
this option. For more information on the IWS, refer to the ER Mapper web site,
http://www.ermapper.com.
14 If necessary change the Colorscale ratio: to 50 and click on the
Recompute desired output size button.
This value is the desired compression ratio that you would like to achieve. For
example, you might specify a ratio of 20:1 for an input file of 1,000MB to achieve
a desired a 50MB compressed image (so the output image is 5% of the size of the
input image).
The Compression Wizard uses the Target Compression ratio as a measure of how
much information content to preserve in the image; i.e as a quality indicator. If,
however, your image has areas that are well suited to compression, a greater rate of
compression may be achieved while still achieving the desired information
content. The actual compression ratio could also be less than the target if you are
compressing small files. The Compression Wizard uses multiple wavelet encoding
techniques at the same time, and adapts and chooses the best technique depending
on the area currently being compressed.
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One example of this is an image that has large areas of water or desert. These can
often be compressed with greater efficiency. Another example is a compressed
image that consists of high resolution airphotos, over lower resolution satellite
imagery where there are no airphotos. Because the satellite images are lower
spatial resolution, greater compression can be achieved in these areas of the image,
while still preserving high quality detail in the airphoto area.
15 Click on the Finish button to start the compression process.
Compression process
A status dialog will display the progress of the compression. When the
compression is complete, a dialog will display the Target and Actual compression
rates.
Except when compressing very small files (less than 2MB in size), the Actual
compression ratio will generally be greater than the Target compression ratio.
Comparing compressed and original images
1 On the main menu, click the Open
button.
An image window and the Open dialog box appear.
2 From the Directories menu, select the \examples path.
3 Open the ‘airphoto_training’ directory, then double-click on the algorithm
‘final_mosaic_map.alg’ to open it.
This is the original image map, which comprises four compressed and mosaiced
airphotos.
4 Re-size the image window to make it larger.
5 Right-click on the image and, from the Quick Zoom menu, select Zoom to
Page Extents.
The image will enlarge so that the map page fills the image window.
6 On the main menu, click on the New
button.
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This will open a second image window.
7 On the main menu, click the Open
button.
An image window and the Open dialog box appear.
8 In the Files of Type: field, select ‘ER Mapper compressed images (.ecw)’.
9 From the Directories menu, select the \examples path.
10 Open the ‘airphoto_training’ directory, then double-click on the file
‘final_mosaic_map_compressed.ecw’ to open it.
This is the compressed image file that you have just created.
11 Re-size this new image window to make it the same size as the other.
12 Right-click on the image and, from the Quick Zoom menu, select Zoom to
All Datasets.
The image will enlarge to fill the image window.
13 Move the image windows so that they are next to one another.
14 Compare the quality of the two images.
The quality should be virtually identical because the original mosaic was made up
of individually compressed images. This is an example of how you could create
mosaics with thousands of large images while conserving disk space. The steps to
follow are:
1. After geocoding the images, compress them and store them on disk.
2. Use the Image Display and Mosaic Wizard to mosaic the compressed images.
3. Use the Balancing Wizard to balance and color match the mosaiced image.
4. Use the Compression Wizard to compress the final image.
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Close both image windows and dialog boxes
1 Close the image window using the window system controls:
•
For Windows, click the
Close button in the upper-right window corner.
2 Click Close on the Algorithm dialog.
Only the ER Mapper main menu should be open on the screen
What you
learned
After completing these exercises, you know how to perform the following tasks in
ER Mapper:
•
Save the image in compressed format using the ECW compressor.
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14
Exporting to GIS
systems
This chapter shows you how to save all or part of a processed mosaic image for use
in a GIS or desktop mapping software product.
About use in GIS systems
Once you have created your mosaic of images in ER Mapper, you may want to
save all or part of the mosaic image in a format suitable for use in a GIS or
Desktop Mapping System (DMS). The procedure you will use depends upon the
raster formats your GIS can accept, and its capabilities for handling large image
datasets.
Note: ER Mapper provides free plug-ins to most GIS or Desktop Mapping System
applications, which allow you to open ER Mapper images directly in those
applications. Formats supported include ER Mapper algorithms, raster datasets,
virtual datasets and ECW compressed images. Where possible, you are advised to
use these plug-ins which are available for download at www.ermapper.com.
Since GIS and desktop mapping systems are usually designed to handle vector
(line/polygon) data, they have limited capabilities for handling raster (image) data.
For example, ER Mapper has no problem handling a 20,000 by 20,000 pixel
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image, but few GIS or DMS applications can do this. When preparing to save an
enhanced image from ER Mapper for use in a GIS or DMS, there are three possible
solutions to this problem:
•
Save the image in ECW compressed format. The high compression rates achieved
by using this format make the image files significantly smaller. You can then use
the applicable free plug-in to open the compressed image in the GIS application.
•
Resample the image to a lower spatial resolution (cell size). This creates much
smaller files, but you lose detail in the image. This may be best if you want to make
a single image file that covers a large geographic area.
•
Subset the airphoto (or mosaic) image into a set of smaller files, each covering a
smaller geographic area. This maintains the original detail in the airphotos and
creates individual files small enough for your GIS or DMS to handle. (It still
requires a large amount of disk space to store all the individual high resolution
files.)
Cropping or subsetting images
Often you will want to crop or subset part of the entire mosaic that covers just an
area of interest, or subset a large mosaic into smaller pieces. There are two basic
steps:
•
Zoom into the desired area. You can do this visually by dragging a zoom box with
the the mouse, or by entering exact coordinates in the Algorithm Geoposition
Extents dialog.
•
Save the area of interest to an external file. You can save to an ER Mapper UDF
(Universal Data Format) dataset (which can be read by many systems), or to a
graphics file such as TIFF.
Spatial resolution (cell size)
Digitized aerial photos are often created at very high resolution; for example one
meter pixel size or even less. This creates very large image files that can be
hundreds of megabytes in size. There are two reasons why you may want to
consider reducing the spatial resolution (cell size) of the exported image:
254
•
GIS/DMS file size limitations–If you want to use an image covering a large
geographic area, you may need to resample the image to a lower spatial resolution
(larger cell size), thus creating a smaller file that can be handled by the GIS product.
•
Detail required for the project–The amount of detail in airphotos is often not
needed for a particular application or project. For example, for updating a general
land use database, it may not be necessary to use imagery with less than 1-meter
resolution. If desired, you can resample the image to the level of detail needed for
the project to create files that are only as large as necessary for the application.
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Raster formats for GIS and DMS products
The two most common formats accepted by GIS and DMS products are TIFF
(Tagged Image File Format) and BIL (band interleaved by line) format.
ER Mapper’s native format is binary BIL, so that is the best solution for products
that can read BIL format. Use the following guide to determine which format you
need to use:
•
ArcView® OR ARC/INFO® –Create an ER Mapper UDF (Universal Data
Format) dataset (in BIL format), which, in addition to the “.ers” header file,
includes a “.hdr” file that allows ArcView® or ARC/INFO® to read the BIL file
directly.
•
Autodesk World™, AutoCAD MAP® or AutoCAD® –Use ER Mapper to save
the image to a TIFF format file.
•
MapInfo–Use ER Mapper to save the image to a TIFF format file. Alternatively,
ER Mapper also provides a free upgrade to MapInfo users that allows MapInfo to
directly read ER Mapper format image files and algorithms. The link automatically
passes the map projection information to MapInfo. This allows users to integrate
very large mosaics of imagery as backdrops into MapInfo quickly and easily.
•
Other GIS and DMS products–Use ER Mapper to save the image to a TIFF or
other compatible graphics format file.
Using compressed images in GIS systems
The ECW Compression Wizard, which is included in ER Mapper, enables you to
save large images in the ECW compressed format with minimal loss in quality.
Compression rates can typically be in the order of 50:1.
The relatively small file sizes of ECW compressed images make them ideal for use
in GIS applications. The free plug-ins available for many GIS products allow you
to open ECW compressed images directly in those products. You can also open
ECW compressed images served over a network (e.g. the Internet) by entering
their URLs. You can then roam over and zoom into the image over the network
from within the application.
Hands-on exercises
These exercises show you how to crop an area of interest from a mosaic image,
save the area as an ER Mapper UDF dataset and a TIFF file.
What you will
learn...
After completing these exercises, you will know how to perform the following
tasks in ER Mapper:
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Before you
begin...
•
Define an exact area of interest using geographic coordinates
•
Save the image as a new UDF dataset
•
Resample the resolution (cell size) of a dataset
•
Save an image as a TIFF format graphics file
Before beginning these exercises, make sure all ER Mapper image windows are
closed. Only the ER Mapper main menu should be open on the screen.
1: Defining an area of interest
Objectives
Learn to define exact areas of interest in an image, and how to subsection an
image into smaller files.
Open the final mosaic algorithm
1 On the main menu, select Open from the File menu.
An image window and the Open dialog appear.
2 From the Directories menu (on the Open dialog), select the path ending
with \examples.
3 Double-click to open the directory named ‘airphoto_training.’
4 Double-click on your ‘airphoto_mosaic.balanced.alg’ algorithm to open it.
The balanced RGB mosaic image displays. Next you define a small area of interest
for your project.
Zoom into the project area
Assume that you have a project to assess the progress and environmental impacts
of the highway interchange in the centre of the mosaic image. The project calls for
an image showing an exact area defined by Easting and Northings values (meters)
in the UTM projection being used.
1 From the View menu, select Geoposition.
The Algorithm Geoposition Extents dialog opens.
2 Click the Extents tab to display the current mosaic extents.
3 Enter the following values in the Eastings and Northings Top Left and
Bottom Right fields:
Top Left - Easting: 484979
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Top Left - Northing: 3621220
Bottom Right - Easting: 486213
Bottom Right - Northing: 3620059
edit values
(Enter/Return
to validate)
4 Click the Apply button.
ER Mapper zooms to the exact extents you entered. You have now defined a
project area to be exported for analysis in your GIS or DMS system.
Also notice that the area is approximately 1.2 by 1.1 kilometers in size (in the
Eastings and Northings Size fields), and that the it displays approximately 1970 by
985 pixels of the mosaic image.
5 Click Close on the Algorithm Geoposition Extents dialog.
2: Creating a UDF dataset
Objectives
Learn to save the area of interest to a new raster dataset in UDF format, and how
to resample the image to a larger cell size (reduce the spatial resolution).
Note: You can also use the following procedure to save your entire mosaic of images to a
single, large ER Mapper dataset. This may be desirable if disk space is not an issue
because displaying and zooming a processed ER Mapper dataset is much faster
than displaying and zooming a mosaic of images that have complex formulas and
other options in the algorithm (where the processing must be executed each time
you zoom or pan).
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Setup the algorithm for dataset output
Saving an image as a dataset is similar to creating an algorithm for the screen
display, except that you are sending the resulting processed image to a new dataset
on disk, instead to an image window on the screen.
1 On the main menu, select Algorithm from the View menu.
The Algorithm dialog opens. Note that this algorithm has red, green and blue
layers to create the RGB color image. You want your output ER Mapper dataset to
also have red, green and blue bands.
2 Examine the layer labels.
The layer labels you see determine what the band labels will be in the new output
dataset. In this case, your output dataset will have three bands labelled ‘Red
Layer,’ ‘Green Layer’ and ‘Blue Layer.’
layer labels become band
labels in output dataset
Note: ER Mapper merges any layers with the same label into a single band in the output
dataset. (So if you have two or more sets of red, green and blue layers, they are
merged into single red, green and blue bands in the output dataset.) To output
layers as individual bands, make sure each layer has a unique label in the
algorithm.
Save the project area to a full resolution UDF dataset
In this case, assume you want to maintain the full resolution of the airphoto data
when you create the output dataset. This guarantees that all the detail in the
airphoto will be carried through to the new dataset.
1 On the main menu, select Save As... from the File menu.
The Save As... dialog opens. This dialog lets you specify the name for the new
dataset to be created, and parameters for the dataset such as data type and size/
resolution.
2 In the Files of Type: field, select ‘UDF (.ers)’.
3 From the Directories menu, select the path ending with the text
\examples.
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4 Double-click on the directory named ‘airphoto_training.’
5 In the Save As: field, enter the filename project_area_full, then click
OK.
This will be the filename for the new UDF dataset.
6 On the Save as UDF dialog, click the Defaults button.
The contents of the four parameters fields on the dialog change to display the
settings and values read from the current algorithm. Notice that:
•
The Output Type field is set to ‘Multilayer’ because there are more than three
layers in the algorithm. You should change this to ‘RGB’.
•
The Width and Height fields are set to the number of pixels displayed in the area
you defined with Geoposition (1432 by 1346). This creates a full resolution
dataset.
Note: You should always click the Defaults button to load the values that pertain to the
current algorithm first, then you can change them as needed.
7 Make sure that the Maintain aspect ratio and Current View options are
selected.
The Current View option limits the image size to the extents currently being
displayed in the image window.
8 Click OK.
ER Mapper creates a new output dataset on disk in the form of three files; the
image data file,with a “.bil” extension, and two header files with a “.ers” and
“.hdr” extension respectively. This enables them to be opened in ER Mapper and
applications like ArcInfo®.
9 Click OK on the completion dialog.
Display the new dataset in RGB
1 On the main menu, select New from the File menu.
A new image window opens.
2 On the main menu, click the Open
button.
The Select a Dataset dialog opens.
3 On the Open dialog, Files of Type field, select either ‘ER Mapper Raster
Dataset (.ers)’ or ‘ESRI BIL and GeoSPOT (.hdr)’.
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You can do this because saving an image as UDF creates the BIL data file with a
.ers and a .hdr header file.
4 From the Directories menu (on the Select File dialog), select the path
ending with the text \examples
5 Double-click on the directory named ‘airphoto_training.’
6 Double-click on the dataset ‘Project_area_full.ers’ or ‘Project_area_full.hdr’
to load it.
Both selections will open the same image.
7 Click OK on the Open dialog.
ER Mapper displays the entire subsetted image as an RGB algorithm.
View information about the new dataset
1 On the Algorithm dialog, click the Load Dataset
button.
The Raster Dataset dialog opens, and your ‘Project_area_full’ dataset is
highlighted (since it is the dataset currently loaded in the layer).
2 On the Raster Dataset dialog, click the Info button.
The Dataset Information dialog opens showing information about the dataset:
It shows the datum and projection, number of rows and columns (image
dimensions, pixel (cell) size in meters (approximately 1-meter resolution), and file
size (about 5.7 Mb in this case).
3 Click Close on the Dataset Information dialog.
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Save the project area to a half resolution UDF dataset
Let us assume that the full detail in the airphoto is not needed, and you would like
to resample the image to approximately two-meter resolution to create a smaller
file for your GIS. One way to do this is to follow the same steps as before, but
divide the default image width and height values by two to create a dataset at half
the original resolution. (You may also want to do this simply to reduce the file size
when covering a large area if your GIS or DMS cannot handle very large images.)
1 Activate the image window containing the original mosaic image (named
‘Final_RGB_mosaic’).
The contents of the Algorithm dialog change to show the mosaic algorithm.
2 On the main menu, select Save As... from the File menu.
The Save As... dialog opens. This dialog lets you specify the name for the new
dataset to be created, and parameters for the dataset such as data type and size/
resolution.
3 In the Files of Type: field, select ‘UDF (.ers)’.
4 From the Directories menu, select the path ending with the text
\examples.
5 Double-click on the directory named ‘airphoto_training.’
6 In the Save As: field, enter the filename project_area_half, then click
OK.
This will be the filename for the new UDF dataset.
7 On the Save as UDF dialog, click the Defaults button.
The contents of the four parameters fields on the dialog change to display the
settings and values read from the current algorithm.
8 Open the Output Type field, select ‘RGB’.
As before, this tells ER Mapper to rescale the real data values into an 8-bit integer
(0-255) data range in the output dataset.
9 Change the values in the Width and Height fields as follows (the original
values divided by 2 and rounded up):
Cells Across (width) = 716
Cells Down (height) = 673
10 Click OK, then click Yes when asked to confirm the dataset creation.
ER Mapper creates a new half-resolution output dataset on disk.
11 Click OK on the completion dialog.
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Note: When creating a new dataset with different cell sizes to the original data,
ER Mapper resamples the original data to the new output cell size during the
process of creating the new dataset. If the ‘Smoothing’ button is turned on in your
algorithm (as in this case), ER Mapper uses bilinear interpolation to create the new
output dataset cell values. If the ‘Smoothing’ button is turned off, ER Mapper uses
nearest neighbor resampling. Bilinear usually creates a nicer looking output image,
so it is recommended that you turn on Smoothing in your algorithm before writing
the new dataset. (If you are creating the dataset at the original resolution, this does
not matter.)
Display the half resolution dataset in RGB
1 On the main menu, select New from the File menu.
A new image window opens.
2 On the main menu, click the Open
button.
The Select a Dataset dialog opens.
3 On the Open dialog, Files of Type field, select either ‘ER Mapper Raster
Dataset (.ers)’ or ‘ESRI BIL and GeoSPOT (.hdr)’.
You can do this because saving an image as UDF creates the BIL data file with a
.ers and a .hdr header file.
4 From the Directories menu (on the Select File dialog), select the path
ending with the text \examples
5 Double-click on the directory named ‘airphoto_training.’
6 Double-click on the dataset ‘Project_area_half.ers’ or
‘Project_area_half.hdr’ to load it.
Both selections will open the same image.
7 Click OK on the Open. dialog.
ER Mapper displays the subsetted and resampled image as an RGB algorithm.
View information about the half resolution dataset
1 On the Algorithm dialog, click the Load Dataset
2 On the Raster Dataset dialog, click the Info button.
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It shows the number of rows and columns is half that of the other dataset
‘Project_area_full,’ the cell size is approximately 2 meters, and the file size is
about 1.4 Mb (25% the size of the full resolution subset image).
Geolink the subset images to see the resolution difference
In order to compare the difference in detail between the full and half resolution
subset images, it is helpful to use ER Mapper’s geolinking feature to tie the two
image windows together. That way, you can zoom to the exact same area in both
windows and see how the different cell sizes affect detail in the data.
Make sure the newest image window (containing the ‘Project_area_half’ dataset)
is active (it should be by default).
1 On the Algorithm dialog, turn off the ‘Smoothing’ option.
Turning off smoothing will allow you to see individual pixels when you zoom in
on a small area later (smoothing would integrate and smooth out pixels).
2 Right-click in the image window, select Quick Zoom, then select Set
Geolink to Window.
The window title bar shows that the window is set to “WINDOW geolink” mode.
3 Activate the other image window containing the ‘Project_area_full’ dataset.
4 On the Algorithm dialog, turn off the ‘Smoothing’ option.
5 Right-click in the image window, select Quick Zoom, then select Set
Geolink to Window.
The window title bar shows that the window is also set to “WINDOW geolink”
mode.
6 Drag a zoom box in one of the windows to zoom on a very small area.
The two windows zoom to the same area automatically, and you should be able to
see individual pixels in the two images. (Zoom in some more if you cannot.)
Notice difference in detail between the two images–this is the effect of resampling
to a larger cell size. So, in exchange for creating a much smaller file (1.4 Mb
versus 5.7 Mb), you must reduce the level of detail in the image.
Note: Geolinking images is a very useful feature for analyzing different images or the
same image in different ways or zoom levels. You can also set these options using
the Geolink tab on the Algorithm Geoposition Extents dialog. See the
ER Mapper Tutorial manual for examples of the different geolink modes, and the
User Guide for more information.
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7 If desired, pan to other areas in both images by clicking – both images will
pan to the same area because they are geolinked in Window mode.
8 Click Close on the Algorithm dialog (you do not need it anymore).
Resampling to an exact cell size
You can also resample an ER Mapper dataset to any desired cell size. This may be
a more intuitive way to resample an image by selecting a cell size rather than using
image dimensions as in the previous procedure. However, this technique requires
an ER Mapper dataset as input (you cannot use an algorithm as in the previous
procedure). To do this:
•
Select Process/Geocoding Wizard.
•
On the Geocoding Wizard Start page, load the dataset to be resampled (.ers file),
and select Rotation, then click on the Rotation Setup tab.
•
On the Rotation Setup page, enter 0 for the Rotation angle, then click on the
Rectify tab.
A rotation angle of 0 ensures that the image is resampled without being rotated.
•
On the Rectify page, enter the desired cell size (in meters) in the Cell size X and
Cell size Y fields.
•
In the File field, enter the file name of the resampled image.
•
If you want to output only a portion of the entire image, first determine the desired
upper-left and lower-right coordinates. Then click Extents on the Rectify page
and enter the desired extents on the Geocode Output Extents dialog.
•
The dimensions and output file size for the resampled dataset at the cell size you
entered are displayed in Output Info box.
•
Select ‘Bilinear’ for Resampling.
•
Click on the Save File and Start Rectification button to create the new
resampled output dataset.
3: Creating a “.hdr” file for ESRI products
Objectives
Learn to create a header (.hdr) file for the full resolution ER Mapper dataset so it
can be read directly by ESRI products.
The ESRI products ArcView® and ARC/INFO® can read image files stored in
binary BIL format, which is also ER Mapper’s internal raster format. If you
already have a ER Mapper dataset, you can simply have ER Mapper create a
“.hdr” file for the dataset so the same image can be read by directly by ESRI
products (without creating a new dataset). If you have saved the image in UDF
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format, as in the previous exercises, ER Mapper has already created the “.hdr” file
so you need not do anything else. You can also use the ER Mapper export facilities
to create the “.hdr” file for a ER Mapper Raster Dataset. This exercise
demonstrates how you would do this.
Close the half resolution subset image window
1 Close the image window containing the half resolution subset image.
(Leave the two other windows open.)
Zoom out on the full resolution subset image
1 If needed, activate the window containing the full resolution subset image.
2 Right-click in the image window, select Quick Zoom, then select Zoom to
All Datasets.
The image zooms out to the full extents of the subsetted project area. (This is not
strictly needed, but helps to simply the following concepts.)
Create the “.hdr” file for the ER Mapper dataset
1 From the Utilities menu, select Export Raster, then ARC/INFO BIL Image
(.hdr), then Export.
The ER Mapper raster file to make ARC/INFO compatible dialog opens.
2 Click the
button next to the File field.
3 From the Directories menu (on the Select File dialog), select the path
ending with the text \examples.
4 Double-click on the directory named ‘airphoto_training.’
5 Double-click on the dataset ‘Project_area_full.ers’ to load it.
6 Turn on the Verbose Messages option.
7 Click OK to start the export process.
ER Mapper displays messages about the export process, including the datum,
projection, cell size and registration coordinate encoded in the “.hdr” file.
The ARC/INFO BIL Image export utility does three things:
•
Renames the ER Mapper binary data file to add a “.bil” file extension (so ESRI
products recognize it as a BIL format image). In this case, the original
‘Project_area_full’ dataset is renamed to ‘Project_area_full.bil.’
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•
Creates a corresponding “.hdr” file for the binary data file (‘Project_area_full.hdr’).
This ASCII header file provides the projection, cell size and parameters needed to
register the image when it is loaded into ArcView or ARC/INFO.
•
Changes the “source file” reference in the ER Mapper header (.ers) file from
‘Project_area_full’ (the previous filename) to ‘Project_area_full.bil.’ This lets you
load and use the dataset in ER Mapper just as you did before.
8 Click Close on the Batch Engine Output dialog to close it.
Close the subset image window
1 Close the subset image window image window containing the full
resolution subset image
You now have now transformed an ER Mapper dataset into an ESRI-compatible
dataset (without actually creating a new image file, only an ASCII header file.)
Note: The above procedure is useful if you already have an ER Mapper Raster Dataset,
and you simply want to create an additional “.hdr” file for it. If you were saving
the image from an algorithm, it would be quicker to save it as ‘UDF’ or ‘ESRI BIL
and GeoSPOT (.hdr)’ type file.
4: Saving a subset image to a TIFF file
Objectives
Learn to save a portion of the airphoto mosaic to a TIFF graphics file. This file
format can be read by most GIS and DMS products.
The original ‘airphoto_mosaic_balanced’ algorithm should be open on the screen.
If you closed it, open it again using File/Open.
Zoom into the project area
For this example, assume that the project calls for an image showing part of the
boat harbor in the lower left corner of the full mosaic image. Again you will define
the exact project area using Easting and Northings values in the UTM projection
system.
1 From the View menu, select Geoposition.
The Algorithm Geoposition Extents dialog opens.
2 Click the Extents tab to display the current mosaic extents.
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3 Enter the following values in the Eastings and Northings Top Left and
Bottom Right fields:
Top Left - Easting: 484037
Top Left - Northing: 3618876
Bottom Right - Easting: 484897
Bottom Right - Northing: 3618114
4 Click the Apply button.
ER Mapper zooms to the exact extents you entered, and shows part of the harbor
area. This is the image you will save to a TIFF file. The area displayed is 860 by
762 meters in size (in the Eastings and Northings Size fields), and 1850 by 1200
pixels of the mosaic image (the Cell X and Cell Y Size fields).
5 Click Close on the Algorithm Geoposition Extents dialog.
Save the project area to a true color (24-bit) TIFF file
In this case, assume you want to maintain the full resolution of the airphoto data
when you create the output dataset. This guarantees that all the detail in the
airphoto will be carried through to the new dataset.
1 On the main menu, select Save As... from the File menu.
The Save As... dialog opens. This dialog lets you specify the name for the new
dataset to be created, and parameters for the dataset such as data type and size/
resolution.
2 In the Files of Type: field, select ‘GeoTIFF/TIFF (.tif)’.
3 From the Directories menu, select the path ending with the text
\examples.
4 Double-click on the directory named ‘airphoto_training.’
5 In the Save As: field, enter the filename project_area_full, then click
OK.
This will be the filename for the new tif file.
6 On the Save as GeoTIFF/TIFF dialog, click the Defaults button.
The contents of the four parameters fields on the dialog change to display the
settings and values read from the current algorithm. Notice that:
•
The Output Type field is set to ‘’RGB’, indicating that it will be saved as a true
color image.
•
The Width and Height fields are set to the number of pixels displayed in the area
you defined with Geoposition (998 by 884). This creates a full resolution dataset.
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Note: You should always click the Defaults button to load the values that pertain to the
current algorithm first, then you can change them as needed.
7 Make sure that the Maintain aspect ratio and Current View options are
selected.
The Current View option limits the image size to the extents currently being
displayed in the image window.
8 Click OK.
ER Mapper creates a new output dataset on disk.
9 Click OK on the completion dialog.
Display the new dataset in RGB
1 On the main menu, select New from the File menu.
A new image window opens.
2 On the main menu, click the Open
button.
The Select a Dataset dialog opens.
3 On the Open dialog, Files of Type field, select ‘GeoTIFF/TIFF (.tif)’.
4 From the Directories menu (on the Select File dialog), select the path
ending with the text \examples
5 Double-click on the directory named ‘airphoto_training.’
6 Double-click on the dataset ‘Project_area_full.tif’.
Both options will open the same image.
7 Click OK on the Open dialog.
ER Mapper displays the entire subsetted image as an RGB algorithm.
View information about the new dataset
1 On the Algorithm dialog, click the Load Dataset
button.
The Raster Dataset dialog opens, and your ‘Project_area_full’ dataset is
highlighted (since it is the dataset currently loaded in the layer).
2 On the Raster Dataset dialog, click the Info button.
The Dataset Information dialog opens showing information about the dataset:
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It shows the datum and projection, number of rows and columns (image
dimensions, pixel (cell) size in meters (approximately 1-meter resolution), and file
size (about 2.6 Mb in this case).
3 Click Close on the Dataset Information dialog.
Save the project area to a half resolution ER Mapper dataset
Let us assume that the full detail in the airphoto is not needed, and you would like
to resample the image to approximately two-meter resolution to create a smaller
file for your GIS. One way to do this is to follow the same steps as before, but
divide the default image width and height values by two to create a dataset at half
the original resolution. (You may also want to do this simply to reduce the file size
when covering a large area if your GIS or DMS cannot handle very large images.)
1 Activate the image window containing the original mosaic image (named
‘Final_RGB_mosaic’).
The contents of the Algorithm dialog change to show the mosaic algorithm.
2 On the main menu, select Save As... from the File menu.
The Save As... dialog opens. This dialog lets you specify the name for the new
dataset to be created, and parameters for the dataset such as data type and size/
resolution.
3 In the Files of Type: field, select ‘GeoTIFF/TIFF (.tif)’.
4 From the Directories menu, select the path ending with the text
\examples.
5 Double-click on the directory named ‘airphoto_training.’
6 In the Save As: field, enter the filename project_area_half, then click
OK.
This will be the filename for the new tiff dataset.
7 On the Save as GeoTIFF/TIFF (.tif) dialog, click the Defaults button.
The contents of the four parameters fields on the dialog change to display the
settings and values read from the current algorithm.
8 Open the Output Type field, select ‘RGB’.
As before, this tells ER Mapper save the image as a real color tiff file.
9 Change the values in the Width and Height fields as follows (the original
values divided by 2 and rounded up):
Cells Across (width) = 500
Cells Down (height) = 443
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10 Click OK, then click Yes when asked to confirm the dataset creation.
ER Mapper creates a new half-resolution output dataset on disk.
11 Click OK on the completion dialog.
Note: When creating a new dataset with different cell sizes to the original data,
ER Mapper resamples the original data to the new output cell size during the
process of creating the new dataset. If the ‘Smoothing’ button is turned on in your
algorithm (as in this case), ER Mapper uses bilinear interpolation to create the new
output dataset cell values. If the ‘Smoothing’ button is turned off, ER Mapper uses
nearest neighbor resampling. Bilinear usually creates a nicer looking output image,
so it is recommended that you turn on Smoothing in your algorithm before writing
the new dataset. (If you are creating the dataset at the original resolution, this does
not matter.)
Display the half resolution dataset in RGB
1 On the main menu, select New from the File menu.
A new image window opens.
2 On the main menu, click the Open
button.
The Select a Dataset dialog opens.
3 On the Open dialog, Files of Type field, select ‘GeoTIFF/TIFF (.tif)’.
4 From the Directories menu (on the Select File dialog), select the path
ending with the text \examples
5 Double-click on the directory named ‘airphoto_training.’
6 Double-click on the dataset ‘Project_area_half.tif’ to load it.
Both options will open the same image.
7 Click OK on the Open. dialog.
ER Mapper displays the subsetted and resampled image as an RGB algorithm.
View information about the half resolution dataset
1 On the Algorithm dialog, click the Load Dataset
2 On the Raster Dataset dialog, click the Info button.
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It shows the number of rows and columns is half that of the other dataset
‘Project_area_full,’ the cell size is approximately 2 meters, and the file size is
about 0.7 Mb (25% the size of the full resolution subset image).
Close the image windows and the Algorithm dialog
1 Close the image windows.
2 On the Algorithm dialog, click the Close button.
Only the ER Mapper main menu is now open on the screen.
What you
learned...
After completing these exercises, you know how to perform the following tasks
in ER Mapper:
•
Define an exact area of interest using geographic coordinates
•
Save the image as a new UDF dataset
•
Resample the resolution (cell size) of a dataset
•
Save the image as a TIFF format graphics file
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Part Two Enterprise
Wide Imagery
About this section
This section of the manual is intended to help explain the problems and solution to
sharing imagery throughout your enterprise, and focuses on free software plug-ins
provided by Earth Resource Mapping. The hands-on exercises in this document
require that certain software and sample data be installed beforehand. Please read
the introduction to each chapter for more information.
Chapter contents
Most chapters in this section give you hands-on experience using the ER Mapper
software plug-ins inside of the host application, such as ArcView GIS, MapInfo,
Autodesk World, and office and word processing applications. In general, each
chapter is independent of the others.
The emphasis is on learning and using the ER Mapper software plug-ins, not on
teaching image processing and remote sensing concepts. For more detailed
information on the principles of image processing or remote sensing for specific
applications, please refer to the ER Mapper Applications Manual, or any of the text
books available.
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15
Enterprise Wide
Imagery
Enterprise wide imagery is the concept of making imagery easily available and
accessible to all users and software applications within your organization. This
chapter explains how you can use free ER Mapper tools to overcome problems with
using and sharing imagery. It also includes a short introduction to imagery, and an
overview of the capabilities of the ER Mapper software.
Using imagery within your organization
Many groups within an organization can benefit from the use of imagery such as
aerial photographs and satellite images in their everyday work. These include
departments such as engineering, marketing, mapping/GIS, graphics, publications
and others. Because these groups use a wide range of software applications, it has
been difficult to share imagery across an entire enterprise. Two primary reasons:
•
Incompatible file formats–Images used by one group cannot be used by other
groups because the file format is not compatible with their software.
•
Large file sizes–Even when your software can read an image file’s format, it often
cannot process large image files. Large image files, such as airphotos, are
increasingly demanded by clients to show high levels of detail and coverage of large
geographic areas of interest.
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•
Images served over the Internet–Images that you access over the internet have to
retrieved via a browser and stored locally before you can use them in your software
application. It would be far more efficient to be able to access images from within
the software application by specifying their URL (Universal Resource Locator) as
you would with an Internet browser like Internet Explorer.
Now ER Mapper provides free software solutions to help you overcome these
problems. Anyone who wants to use imagery can do so without having to convert
between formats, reduce file sizes, learn complex imaging products, and so on.
Enterprise wide imagery
Enterprise wide imagery is the concept of making imagery easily available and
accessible to all users and software applications within your organization. These
applications include desktop mapping and GIS products, graphics and presentation
products, word processing products, database products, and others.
Sharing Imagery Throughout an Enterprise
Publications
(Word, FrameMaker,
AmiPRO, etc.)
Graphics
(Photoshop, Powerpoint,
Corel Draw, etc.)
Imagery Files
(TIFF, BMP, JPEG, HDR,
ERS, ECW, ALG)
Engineering
(CAD software, AutoCAD,
AutoCAD Map)
Business/Marketing
(MapInfo, spreadsheet,
database, etc.)
Mapping/GIS
(ArcView, ARC/INFO,
Intergraph, etc.)
ER Mapper’s free imagery products provide solutions to the two main problems:
•
278
Incompatible file formats–Images used by one group can now be used by all
groups because ER Mapper’s free solutions allow most products to read an industry
standard set of imagery formats. For example, word processing or graphics
applications can now directly display satellite images in their native formats.
Enterprise Wide Imagery
Chapter 15 Enterprise Wide Imagery ● ER Mapper free imagery solutions
•
Large file sizes–ER Mapper’s free solutions allow your applications to read image
files of virtually any size very quickly. Mosaics of aerial photographs, for example,
often require 100’s of megabytes (even gigabytes) of disk space. ER Mapper’s
solutions handle the underlying technology, so even simple word processors can
display very large image files in a snap.
•
Images served over the internet–ER Mapper 6.1 allows you to directly access
images served over the internet by specifying their URL. The free plug-ins allow
most other GIS and Office products to do the same.
ER Mapper free imagery solutions
ER Mapper’s free Enterprise Wide Imagery solutions are tightly integrated
software tools and plug-ins that let you share images throughout your enterprise.
•
ER Viewer–A free image viewer that lets you view ER Mapper images and
algorithms, TIFF and GeoTIFF files, Windows BMP, JPEG, Universal Data Format
(UDF), ESRI BIL, and SPOTView image formats.
•
Imagery plug-in for Office users–Users of office products (word processing,
graphics, spreadsheets, etc.) can use ER Viewer’s OLE capabilities to directly
display large imagery files quickly within their applications.
•
ER Mapper Imagery Extension for ArcView GIS–A free extension that lets
ArcView GIS users display ER Mapper format images and smart data algorithms.
•
MapImagery plug-in for MapInfo–A free plug-in that lets MapInfo users display
and enhance the same image formats supported by ER Viewer.
•
AutoCAD Map plug-in–A free plug-in that lets AutoCAD Map users display the
same image formats supported by ER Viewer.
•
Autodesk World imagery viewer–Autodesk World lets users display any images
supported by ER Viewer (this functionality is embedded in the World software).
Using ER Mapper for imaging
By using the plug-ins and tools in conjunction with ER Mapper, you gain access to
the powerful capabilities of this leading integrated mapping and image processing
application. ER Mapper can be used as a central depository for all image data,
where it can be processed as needed before passing on to other applications in you
organization via the plug-ins and tools.
Adding ER Mapper to your enterprise gives you capabilities to:
•
Import and display over 100 different image formats
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•
Directly read TIFF, GeoTIFF, BMP, ER Mapper images and algorithms, ESRI BIL,
SPOTView and Universal Data Format (UDF) imagery without the need for import
or conversion
•
Easily view the entire project area in one image–no limits on image file sizes
•
Geocode and orthorectify imagery easily to precisely register with GIS vector data
•
Automatically display, mosaic and color balance numerous images
•
Combine imagery, vector and tabular data from any number of sources
•
Create and edit vector data over imagery backdrops, and highlight features of
interest and save them as vectors with ER Mapper’s raster to vector conversion tools
•
Use advanced image processing functions such as contrast enhancement,
multispectral classification, vegetation indexes, color shaded reliefs, filtering,
merging images, and many others.
airphotos
satellite images
digital elevation models
geophysical data
ASCII and binary
(over 100 image formats)
ER Mapper
(image processing, mosaicing,
geocoding, map production,
3D visualization...)
Autodesk World
ArcView GIS
AutoCAD MAP
MapInfo
Office applications
ER Viewer
(image viewing)
ER Mapper can serve as a central hub for all the image data, so you can process and
enhance images if needed before passing them onto other applications in your
enterprise.
ER Mapper image compression
ER Mapper also lets you create and distribute royalty-free compressed images
using the patent pending ER Mapper ECW Compression facilities and the free
plug-ins for other applications. You can now achieve significant compression ratios
with no noticeable deterioration in image quality.
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Chapter 15 Enterprise Wide Imagery ● Working with large images
Working with large images
When working with satellite imagery, airphotos, scanned topographical maps and
other types of imagery, the size of image files can become very large. For example,
it takes 3 terrabytes (3,000GB) of color imagery to take aerial photographs of
typical city at 3 inch resolution. It takes 1.5TB (1,500GB) of color imagery to cover
all of California at a resolution of one meter.
Compression of imagery offers several advantages including:
•
reduced image file size
•
faster access
•
easier distribution
•
the ability to work with imagery covering larger areas
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16
Using ER Viewer
This chapter explains how to use the free ER Viewer application to display and
analyze several types of image files. ER Viewer is a free Windows application that
can be installed from the ER Mapper installation CD-ROM or downloaded from
the ER Mapper website at www.ermapper.com.
About ER Viewer
ER Viewer is a free, easy to use image viewing application featuring interactive
roaming and zooming of very large image files. It also acts as an OLE server
application to let you view images inside your favorite Windows applications.
ER Viewer offers unequalled stability and supports a wide range of image formats,
including:
•
Universal Data Format (UDF) images
•
ER Mapper compressed and uncompressed images
•
TIFF and GeoTIFF images
•
Windows BMP images
•
SPOTView images
•
ESRI BIL (ARC/INFO and ArcView) images
•
Smart Data ER Mapper algorithms
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Chapter 16 Using ER Viewer ● Hands-on exercises
Hands-on exercises
These exercises show you how to use ER Viewer to display image files and perform
zooming, roaming and measuring distances.
What you will
learn...
After completing these exercises, you will know how to perform the following
tasks in ER Viewer and OLE-enabled Windows applications:
•
Use ER Viewer to display images in several different formats
•
Interactively zoom and roam images
•
View geographic coordinates and measure distances on an image
•
Print an image (optional)
Before you
begin...
Before beginning these exercises, you must have installed ER Viewer on your
system. You can download it free of charge from the ER Mapper web site at
www.ermapper.com if needed.
Note: The following examples use image files supplied with ER Mapper as sample data.
If it is not possible to install ER Mapper, you must have a sample TIFF or BMP
image file to use for the exercises.
1: Using ER Viewer to display images
Objectives
Learn how to use ER Viewer to display images, zoom and roam around the
images, and measure distances on geocoded images.
Start ER Viewer
1 Start ER Viewer by double-clicking the
icon on your desktop or
selecting Start/Programs/ER Mapper/ER Viewer.
ER Viewer starts up and displays the Getting Started information dialog that
contains basic instructions for using ER Viewer.
2 Click Close on the Getting Started With ER Viewer dialog.
3 Click the Maximize
button in the upper-right corner of the ER Viewer
window (if it is not already maximized)
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ER Viewer expands to fill your desktop.
About the ER Viewer interface
The ER Viewer user interface has the following components:
main menu
toolbar
image window
coordinates of current
mouse position and
distance measurement
status bar
Tip:
To get help on using any ER Viewer component, click the What’s this?
button then and click on the component of interest.
Open an ER Mapper-format image file
1 Click the Open
toolbar button (or select File > Open).
2 On the Open algorithm or image files dialog, open the Files of type
menu.
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A list of image formats supported by ER Viewer displays. You can open
ER Mapper-format images and algorithms, graphics formats like TIFF and BMP,
satellite image formats such as GeoSPOT and ESRI BIL, and others.
3 Select the All image files option.
4 Navigate to the directory where ER Mapper is installed. Open the
‘examples\Shared_Data’ directory. Double-click on the file ‘airphoto.ers.’
ER Viewer displays an aerial photograph of the San Diego, California area. (This
file was previously imported and saved in ER Mapper ‘.ers’ image file format.)
Note: If the ER Mapper sample data is not installed, navigate to a directory containing an
image in TIFF, BMP or other supported format an open it instead.
Enlarge the image window
1 Drag the image window by a corner to make it larger.
2 From the Zoom menu, select Data Extents.
The image expands to fill the new image window size.
Use the Zoom Tool to zoom freely in and out
1 Click the Zoom Tool
button on the toolbar (or press F6).
2 Point to the center of the image, then drag downward to zoom in.
3 Point to the center of the image, then drag upward to zoom out.
By dragging up or down, you can zoom in or out by any amount. When you release
the mouse, ER Viewer refreshes the image detail as needed.
Use the Zoom Tool to zoom by fixed amounts
1 From the Zoom menu, select Data Extents.
The airphoto image zooms out to show the entire image extents.
2 Click on the center of the image to zoom in.
The image zooms in to twice (200%) the previous magnification.
3 While holding down the Ctrl key, click the image center again.
The image zooms out to half (50%) of the previous magnification. With the Zoom
Tool
selected, clicking zooms in and Ctrl-clicking zooms out by fixed
amounts.
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Use the Zoom Box Tool to zoom on an exact area
1 From the Zoom menu, select Data Extents.
The image zooms out to show the entire image extents.
2 Click the ZoomBox Tool
button (or press F5).
3 Drag a box around the central portion of the image.
ER Viewer zooms in to display the area you defined with your box. Use the
ZoomBox Tool tool to zoom in on an exact area of interest.
Use the Hand Tool to roam around (pan) the image
1 Click the Hand Tool
button (or press F7).
2 Drag the airphoto within the image window.
ER Viewer roams (or pans) to display the adjacent area of the image. Use the Hand
Tool tool to roam around and quickly view adjacent areas of the image.
Tip:
When the Zoom Tool
Hand Tool
is selected, pressing Shift temporarily enables the
.
View geographic locations on the image
1 Without depressing the mouse, point to different locations on the image.
The geographic locations of the current mouse position are shown in the lower right
part of the ER Viewer window. (Locations are shown in the units of the map
projection. This airphoto is registered to the UTM coordinate system, so the
locations are in meters of Easting and Northings.)
Note: Geographic locations only display when your image has been registered to a map
projection. If your image in unregistered, the locations appear as row and column
(cell) values instead.
Use the Measure Tool to measure distances in the image
1 Click the Measure Tool
button (or press F8).
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2 Drag a line between two points on the image.
drag a line, distance
is shown in status bar
ER Viewer shows the distance between the start and end points on the right side of
the status bar.
3 While keeping the mouse button depressed, drag to different points on the
image.
The distances are updated interactively as you move the mouse. As with locations,
distances are shown in the units of the map projection (in this case meters).
Tip:
Ctrl-Shift temporarily enables the Measure Tool
, ZoomBox Tool
or Hand Tool
Open a second ER Mapper image file
1 Click the Open
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when the Zoom Tool
is selected.
Chapter 16 Using ER Viewer ● 1: Using ER Viewer to display images
2 Navigate to the directory where ER Mapper is installed. Open the directory
‘examples\Applications\Land_Information.’
Tip:
The ‘Automatically adjust contrast on dataset load’ option enhances the contrast of
any image you open automatically. You should usually leave this option turned on.
3 Double-click on the file ‘SPOT_XS_07Aug88.ers’ to display it.
ER Viewer displays a SPOT XS satellite of the San Diego, California area in a new
image window. This is a color infrared image, so vegetated areas are shown in red
tones.
4 Make the image window two times larger, then select Zoom > Data
Extents.
5 Zoom in to an area of interest using the Zoom Tool
or ZoomBox Tool
.
6
Pan or scroll the image as desired using Hand Tool
.
View properties of the image file
1 From the View menu, select Properties.
ER Viewer displays tab pages showing properties of the image file.
2 On the Properties dialog, click the Registration tab.
The geodetic datum, map projection, units and other georeferencing information
about the image file is shown.
3 Click Cancel on the Properties dialog.
Preview a hardcopy print of the image
1 Click the Print Preview
button.
ER Viewer redisplays the image to show how it would be sized and positioned on
your default printer. ER Viewer tries to center the image on the page and fill the
printable area.
Tip:
Only the area you zoomed into will be printed, so you can easily print any portion
of a large image.
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2 Click Close or click the
button on the image window.
The image redisplays in normal mode for zooming and roaming.
Print of the image (optional)
1 Click the Print
button.
The Windows Print dialog for your default printer opens to let you select a printer,
change the properties, and print the image.
2 If desired, select the printer and properties, then click OK to print the image.
Otherwise click Cancel to close the Print dialog.
Close ER Viewer
1 Click the Close
What you
learned
290
button on the ER Viewer window (or select File > Exit).
After completing these exercises, you know how to perform the following tasks in
ER Viewer:
•
Use ER Viewer to display images in several different formats
•
Interactively zoom and roam images
•
View geographic coordinates and measure distances on an image
•
Print an image (optional)
Enterprise Wide Imagery
17
Office applications
(OLE)
This chapter explains how you can use your office software’s OLE capabilities to
easily display and manipulate large images inside Windows applications (without
having to save the image as part of the file).
Note: To use the OLE capabilities described here, make sure you first install ER Viewer
and perform the exercises in the previous chapter to become familiar with it. You
can install ER Viewer from the ER Mapper installation CD-ROM or download it
from the ER Mapper website at www.ermapper.com.
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Chapter 17 Office applications (OLE) ● What is OLE?
What is OLE?
Many Windows applications support OLE–Object Linking and Embedding. OLE is
a program-integration technology developed by Microsoft that lets you easily share
information between programs. This capability allows you to insert an object (such
as an image) into any OLE-enabled application. Most office applications running
under Microsoft Windows support OLE.
Image file
(source file)
image
object
spreadsheet
document
image
object
image
object
presentation
document
word
processing
document
With a linked object, information is created in one file (the source file) and inserted
into another file (the destination file) while maintaining a connection or “link”
between the two files. When you save the destination file (such as a word
processing document), you save only the link to the source file and do not embed
the image as part of the document.
For example, several different documents can display the same image, all via links
to the single source image file. If the source image file is modified, the linked
image objects in the destination files are also automatically updated to reflect any
changes.
Sharing image files using OLE
In addition to letting you view images, ER Viewer also acts as an OLE server
application to let you view images inside your favorite Windows applications.
Using ER Viewer’s OLE capabilities provides many advantages for sharing large
image files throughout your enterprise, including:
292
•
You can display image files much larger than the application itself is capable of
displaying (for example a 500MB airphoto) since ER Viewer performs the
processing (not the application where the image is displayed)
•
Much faster display of large image files in documents, since ER Viewer performs
the processing (not the application where the image is displayed)
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Chapter 17 Office applications (OLE) ● Hands-on exercises
•
Word processing documents, spreadsheets, presentations, and other applications can
all share a single copy of the original imagery files
•
Documents can display images in many additional image formats not supported by
the destination application, but that are supported by ER Viewer
•
Images can be displayed in the application without having to permanently embed
and save the image files as part of the document (so the documents remain small in
size)
•
You can access the power of ER Mapper Smart Data Algorithms to apply complex
processing enhancements that create beautiful images interactively without
changing the original image files
Hands-on exercises
These exercises show you how to insert an image into another Windows application
as a linked OLE object using ER Viewer as the source application.
What you will
learn...
Before you
begin...
After completing these exercises, you will know how to perform the following
tasks in OLE-enabled Windows applications:
•
Insert an image as a linked OLE object into another Windows application
•
Edit the image object within the application using the ER Viewer toolbar
•
Copy and paste an OLE image form one area to another
Before beginning these exercises, you must have installed ER Viewer on your
system.
Note: The following examples use image files supplied with ER Mapper as sample data.
If it is not possible to install ER Mapper, you must have a sample TIFF or BMP
image file to use for the exercises.
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1: Using OLE to display images
Objectives
Learn how to use ER Viewer as an OLE server to display and edit large image
files within OLE-enabled Windows applications.
In the past, it was usually necessary to embed large image files in word processing
documents, spreadsheets or presentations in order to display and print them at full
resolution. Since the image file was saved as part of the document, it created very
large document files and the data could not be edited once it was inserted.
With Object Linking and Embedding (OLE), you can use ER Viewer as a powerful
image viewing engine to display and edit large image files directly inside your
Windows applications. This allows you to display images in many formats that
cannot be read by the application itself, and also makes the document files much
smaller because only a link to the image file is saved with the document.
The following example uses Microsoft Word as the example OLE-enabled
application. You can use any other OLE-enabled word processing application if
desired (WordPerfect, Framemaker, and so on).
Start Microsoft Word (or other OLE-enabled word processor)
1 Start up the Word application on your system (or another OLE-enabled
word processor).
2 Type the text San Diego Airphoto as the first line of your document,
then press Enter to create a new line.
Open the Windows Explorer
1 Open the Windows Explorer application (select Start > Programs >
Windows Explorer).
2 Open the ER Mapper installation directory. Then open the directory
‘examples\Applications\Airphoto\1_Geocoding.’
You should see a list of files beginning with ‘San_Diego_Airphoto.’
3 Move the Word application window and the Explorer window side by side
(resize them if needed).
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Drag an image file into the Word document
1 Drag the file ‘San_Diego_Airphoto_36_rectified.ers’ from the Explorer
window and drop it into the Word document window.
After a short time, the image file displays in your document.
2 In the word processor, click once on the image to select it, then drag the
lower-right corner handle to make it much larger.
The image redisplays at the larger size. This image is a color aerial photograph of
the San Diego, California area. The source image file is over 34MB in size.
Zoom and roam using the ER Viewer toolbar
1 In Word, double-click on the image.
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The word processor’s native toolbar changes to display the ER Viewer zoom and
roam tools. When you double-click on a linked object, the object’s server
application (ER Viewer) is temporarily enabled inside the container application
(the word processor) so you can edit the object.
ER Viewer toolbar
2 Click the ZoomBox Tool
button, then drag a box to enclose the area of
white buildings in the lower central portion of the image.
3 ER Viewer zooms in to display the area you defined with your box.
4 Click the Hand Tool
button, then drag the image.
5 ER Viewer roams (or pans) to display the adjacent area of the image.
Return to the Word application
1 In the word processing document, click outside the image area.
The usual word processor toolbar and interface returns, and the image is updated to
the new extents you defined.
Drag and drop a second image into the document
1 Press Enter twice to create two new lines below the image, then type the
text Mount St. Helens Volcano.
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2 In the Explorer window, open the ER Mapper home directory, then open the
directory examples\Applications\Mt_St_Helens.
3 Drag the file ‘2D_after_eruption.alg’ from the Explorer window and drop it
into the word processing document window.
After a short time, the image file displays in your document.
4 Click once on the image to select it, then drag the lower-right corner handle
to make it larger.
This is an image of the Mount St. Helens Volcano in the state of Oregon, USA after
an eruption that blew out the central portion of the mountain. The image data from
which this is created is a Digital Elevation Model (DEM) where each pixel value
represents a terrain elevation. The special processing technique is called a
“colordrape” that combines a color image that shows elevation with a shaded relief
image that shows terrain features.
In this case, the image file you linked to is an ER Mapper Smart Data Algorithm
(.alg). The algorithm file runs the ER Mapper processing engine in the background
to interactively create the enhanced colordrape image from the original DEM
image data.
Tip:
Most OLE-enabled applications also let you insert a linked OLE object into a
document using a menu command (as an alternative to the drag and drop method
shown in the previous example).
Zoom into and center the volcano image
1 Double-click on the inserted image to display the ER Viewer toolbar.
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2 Use the Zoom Tool
to zoom in on the central portion of the image (the
volcanic caldera), then use the Hand Tool
center it.
to drag the image and
Use tools to zoom
in and center image
3 When finished, click outside the image to return to the word processing
application.
Copy and paste the volcano image
1 Click once on the volcano image to select it.
2 Press Ctrl+C (or select Edit > Copy) to copy it.
3 Press Enter twice to create two new paragraphs in your document.
4 Press Ctrl+V (or select Edit > Paste) to paste the volcano image into the
new location.
It is sometimes useful to copy and paste OLE images from one part of your
document to another. For example, you might insert an airphoto covering a large
area, then copy and paste it to different parts of the document and zoom in to show
different areas of interest.
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(Optional) Save your word processing document.
1 Save your document, then close the application.
Note: If you check the file size of your word processing document, it should only be
about 1MB. Yet this document displays images that are created from almost 40MB
of image files. This is one of the big advantages of OLE–you can display very large
image files inside a document very quickly without having to embed the image
files. (That is, images are not saved as part of the document, only the link to them is
saved.)
What you
learned
After completing these exercises, you know how to perform the following tasks in
OLE-enabled Windows applications:
•
Insert an image as a linked OLE object into another Windows application
•
Edit the image object within the application using the ER Viewer toolbar
•
Copy and paste an OLE image from one area to another
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18
ArcView GIS
Users
This chapter explains how to use the free ER Mapper Imagery Extension for
ESRI’s ArcView GIS software. It also explains how to obtain and install the
extension, and the additional imaging capabilities ArcView users can gain by using
the extension in conjunction with ER Mapper.
Note: You must have a licensed copy of ArcView GIS version 3.1 or greater to install and
run the ER Mapper Imagery Extension. You do not need to have a copy of
ER Mapper installed, but this is recommended to gain access to sample ER Mapper
imagery and algorithms used in the following tutorial. (You can order the free
ER Mapper installation CD-ROM from www.ermapper.com.)
About the ER Mapper Extension for ArcView GIS
As imagery data sources become more important for GIS applications, the need to
efficiently process, enhance and display large image files also becomes more
important. Earth Resource Mapping (developers of ER Mapper) provides a free
extension (or “plug-in”) that lets ArcView GIS users directly display ER Mapper
imagery and algorithms. With the ER Mapper Imagery Extension, ArcView GIS
users are no longer restricted by limited image handling capabilities. In addition,
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you can experience the full power of ER Mapper algorithms from within ArcView
GIS, and give your vector GIS data real world meaning by presenting it over image
backdrops.
Using the extension with ER Mapper
By using the extension in conjunction with ER Mapper, ArcView GIS users gain
access to the extensive capabilities of this powerful integrated mapping and image
processing software, including:
•
Import and display over 100 different image formats
•
Directly read TIFF, GeoTIFF, BMP, ER Mapper images and algorithms, ESRI BIL,
SPOTView and Universal Data Format (UDF) imagery without the need for import
or conversion
•
Easily view the entire project area in one image–no limits on image file sizes
•
Geocode and orthorectify imagery easily to precisely register with GIS vector data
•
Automatically display, mosaic and color balance numerous images
•
Combine imagery, vector and tabular data from any number of sources
•
Create and edit vector data over imagery backdrops, and highlight features of
interest and save them as vectors with ER Mapper’s raster to vector conversion tools
•
Use advanced image processing functions such as contrast enhancement,
multispectral classification, vegetation indexes, color shaded reliefs, filtering,
merging images, and many others.
How to obtain the ER Mapper Imagery Extension
You can obtain the free ER Mapper Imagery Extension from two sources:
302
•
The ER Mapper installation CD-ROM–The extension can be installed as a
separate component from the ER Mapper installation CD-ROM. (It is recommended
that you also install ER Mapper to gain access to a wide variety of sample data and
test drive the software in free evaluation mode to see what it can do for you.)
•
The ER Mapper web site–You can download the latest version of the extension
from the ER Mapper web site at www.ermapper.com. Navigate to the “free
software” area and download the ArcView GIS plug-in.
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Chapter 18 ArcView GIS Users ● Hands-on exercises
Hands-on exercises
These exercises show you how to use the ER Mapper Imagery extension for
ArcView GIS.
What you will
learn...
Before you
begin...
After completing these exercises, you will know how to perform the following
tasks in ArcView GIS using the ER Mapper Imagery Extension:
•
Enable the ER Mapper Imagery Extension after starting ArcView GIS
•
Display an ER Mapper image file (.ers) as an Image Data Source
•
Display an ER Mapper algorithm file (.alg) as an Image Data Source
•
Display a vector theme on an ER Mapper image
Before beginning these exercises, you must have installed ArcView GIS version
3.1 or higher and the ER Mapper extension for ArcView on your system. These
exercises use sample ER Mapper imagery and algorithm files from the
ER Mapper installation CD-ROM. You may also follow the general procedures
using your own ER Mapper imagery (.ers) or algorithm (.alg) files.
1: Using the ER Mapper extension
Objectives
Learn to enable the ER Mapper extension for ArcView and display ER Mapper
imagery (.ers) files and algorithm (.alg) files.
Start ArcView GIS
1 Start the ArcView GIS software on your system.
2 If the Welcome to ArcView GIS dialog appears, click Cancel.
3 Click the Maximize
button in the upper-right corner of the ArcView GIS
application window (if it is not already maximized)
ArcView GIS expands to fill your desktop.
Load the ER Mapper extension
1 From the File menu, select Extensions....
2 On the Extensions dialog, click on the box next to ‘ER Mapper Algorithms
and Imagery’ (a check mark should appear).
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3 Turn on the ‘Make Default’ option, then click OK.
turn on ER Mapper
extension
load extension
on startup
The ER Mapper Imagery Extension for ArcView GIS loads. You can now display
ER Mapper algorithm and imagery files. Since you selected ‘Make Default,’ the
extension will load automatically each time you start ArcView GIS.
Open an ER Mapper-format (.ers) image file
1 If the Project window is not open, select File > New Project.
2 On the Project window, click New to open a View window. (It should titled
‘View1’.)
3 Click the Add Theme
button (or select View > Add Theme).
4 On the Add Theme dialog, select ‘Image Data Source’ from the ‘Data
Source Types’ list. (ER Mapper imagery and algorithms are always image
data sources in ArcView GIS.)
5 Double-click on the folder where ER Mapper is installed. Then open the
‘examples\applications\land_information’ folder.
A list of ER Mapper imagery (.ers) and algorithm (.alg) files appears.
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6 Scroll down to the bottom, then double-click on the file
‘spot_xs_07aug88.ers.’
load image
7 Click the check box next to the ‘Spot_xs_07aug88’ theme to turn it on.
ArcView GIS displays a SPOT XS color satellite image of the San Diego,
California area. This is a 3-band color infrared image, so vegetated areas appear in
red tones.
turn on theme
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This image file is in ER Mapper’s native ‘.ers’ imagery format. The extension
enables ArcView GIS to read it as one of its native formats. (ER Mapper’s imagery
format is composed of a binary data file and an ASCII header ‘.ers’ file similar to
the ‘.hdr’ files also used by ESRI products.)
8 Resize the ‘View1’ window to make the image larger.
Zoom, pan and measure the image
1 Click the Zoom In
tool, then drag a box over the central part of the
SPOT image to zoom into it.
2 Click the Pan
3 Click the Measure
area.
tool, then drag the image to view adjacent areas.
tool, then drag a line to view distances across an
The line length appears in the lower-left corner of the ArcView GIS dialog.
4 Move the mouse pointer around inside the image.
Geographic coordinates appear in the upper-right area indicating that the image is
georeferenced. (In this case to the UTM projection, so units are meters of Easting
and Northings.)
Tip:
When you load an ER Mapper imagery (.ers) file, the contrast is automatically
enhanced by the ER Mapper Imagery Extension (using a 99% linear contrast
stretch). You can further adjust image contrast if desired using Theme > Edit
Legend, however this is usually not necessary.
Open an ER Mapper algorithm (.alg) file
In ER Mapper, an algorithm is a list of processing steps or instructions ER Mapper
uses to transform a raw imagery file into a final, enhanced image on your screen or
printer. Algorithms let you define a “view” into your data that you can save, reload,
and modify at any time. By using the ER Mapper Imagery Extension, you can
display ER Mapper algorithms just like an other image data source.
Tip:
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You need a license for ER Mapper to create algorithms, but you only need the free
ER Mapper Imagery Extension to view them in ArcView GIS. This means that
anyone using ER Mapper can create algorithms and send them to you for viewing.
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1 From the Edit menu, select Delete Themes. When prompted to delete the
theme ‘Spot_xs_07aug88.ers’ click Yes.
The theme is deleted from your view.
2 Click the Add Theme
button (or select View > Add Theme).
The files in the ‘land_information’ directory should be displayed.
3 Open the ‘applications\airphoto\3_balancing’ folder.
A list of ER Mapper imagery (.ers) and algorithm (.alg) files appears.
4 Scroll down to the bottom, then double-click on the file
‘san_diego_airphoto_34_36_balanced_mosaic.alg’ (the next to last file).
balanced mosaic algorithm
5 Click the check box next to the theme to turn it on.
ArcView GIS displays a mosaic of two orthorectified color airphotos of the
downtown San Diego, California area. This image is created from an ER Mapper
algorithm, so it has several processing enhancements applied to the two airphoto
imagery (.ers) files used as input:
•
brightness and color variations within each image are normalized to remove
“hotspots” or light-to-dark variations across each photo
•
the contrast and brightness of the two normalized images are then balanced to each
other ensure uniform color and brightness across the mosaic
•
the seam between the two images is feathered to ensure a smooth transition between
the two images and make the mosaic truly “seamless”
6 Click the Zoom In
tool, then drag a box over the central part of the
mosaic image to zoom into it.
7 Click the Pan
tool, then drag the image to view adjacent areas.
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This example shows how you can access the power of ER Mapper algorithms to
apply complex image enhancements and display them directly with ArcView GIS.
This example uses only two airphotos, but you could just as easily display a mosaic
algorithm containing 100’s of megabytes (even gigabytes) of airphoto images.
Add a second view to display a merged satellite image
1 Click the Minimize
close it if desired).
button on the ‘View1’ window to minimize it (or
2 On the Project window, click New to open a new View window. (It should be
titled ‘View2’.)
3 Click the Add Theme
button (or select View > Add Theme).
The files in the ‘3_balancing’ directory should be displayed.
4 Open the ‘examples\functions_and_features\data_fusion’ folder.
A list of ER Mapper algorithm (.alg) files appears. These algorithms all show
different ways of merging (or “fusing”) two different images into one.
5 Double-click on the file ‘brovey_transform.alg.’
6 In the ‘View2’ window turn on the ‘Brovey_transform’ theme.
ArcView GIS displays a color image of the San Diego, California area. This is a
merge of a Landsat TM satellite image (bands 5, 4 and 2) and a SPOT
Panchromatic satellite image. By merging the two types of data, you get the high
spatial detail provided by the SPOT Pan image (10-meter resolution) with the
multispectral color information provided by the Landsat TM image (seven bands at
30-meter resolution).
The Brovey Transform is a mathematical way of combining the two images that
also greatly enhances the color. Merging or fusion techniques like this are used to
combine the strengths of different satellite sensors and create up-to-date views of
the earth’s surface.
7 Enlarge the ‘View2’ window to make the image larger.
8 Zoom in and pan to different parts of the image using the Zoom In
Pan
and
tools.
The image shows a high resolution, color-enhanced view of the area. As with the
airphoto mosaic, the ER Mapper algorithm creates this image interactively from the
two separate Landsat and SPOT satellite imagery files. (The Brovey Transform
technique usually requires up to three intermediate image files to be created when
using traditional imaging software, but ER Mapper performs the processing in real
time from the two source images without creating intermediate files.)
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9 Click the Zoom to Full Extent
button (or select View > Full Extent) to
zoom out to the full image extents again.
Add a second theme (algorithm) showing thematic land cover
1 Click the Add Theme
button (or select View > Add Theme).
The files in the ‘data_fusion’ directory should be displayed.
2 Open the ‘functions_and_features\classification_display’ folder.
3 Double-click on the file ‘isoclass_classification.alg.’
4 In the ‘View2’ window turn on the ‘isoclass_classification’ theme.
ArcView GIS displays a thematic color image of the same area of San Diego.
Different colors correspond to different types of landuse in the area. This image
was created from a 1985 Landsat TM satellite image using ER Mapper’s
ISOCLASS unsupervised classification feature. Classification groups pixels with
similar spectral values into classes that can represent different types of landuse or
land cover.
5 Turn the ‘isoclass_classification’ theme on and off to compare it with the
‘brovey_transform’ merged satellite image theme.
Adding several themes showing different types of data or processing techniques as
backdrop images can be very helpful to aid analysis of your vector GIS data.
Add a third theme (algorithm) showing topography
1 Click the Add Theme
button (or select View > Add Theme).
The files in the ‘classification_display’ directory should be displayed.
2 Open the ‘examples\data_types\digital_elevation’ folder.
A list of ER Mapper algorithm (.alg) files appears. These algorithms all show
different ways displaying and processing digital elevation model (DEM) data files.
3 Double-click on the file ‘colordrape.alg.’
4 In the ‘View2’ window turn on the ‘Colordrape.alg’ theme.
ArcView GIS displays a color shaded relief (or “colordrape”) image of the same
area of San Diego. Colors represent elevation (reds are highest) and the shading
effect highlights topographic features such as hills and valleys. This image is
illuminated from the northeast, so shadows appear on the southwest side of terrain
features. ER Mapper has a built-in “realtime shading” feature that lets you
interactively change the shading parameters without creating output files.
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5 Turn the three themes on and off to compare them (if more than one is on,
the top theme covers the others).
turn on any
theme (drag
and drop to
reorder)
Add a third view to display an image and vector data
1 If desired, click the Minimize
it.
button on the ‘View2’ window to minimize
2 On the Project window, click New to open a new View window. (It should be
titled ‘View3’.)
3 Click the Add Theme
button (or select View > Add Theme).
The files in the ‘digital_elevation’ directory should be displayed.
4 Open the ‘examples\shared_data’ folder.
A list of ER Mapper image (.ers) and algorithm (.alg) files appears.
5 Double-click on the file ‘airphoto.ers.’
6 In the ‘View3’ window turn on the ‘Airphoto’ theme.
ArcView GIS displays a color aerial photo of a small area near downtown San
Diego, California.
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Overlay vector roads (in DXF format) on the airphoto
You can display any vector data such as shapefiles, coverages, and other supported
vector formats on your ER Mapper image data. In this example, you will overlay a
vector roads file of the corresponding area stored in DXF format.
1 From the File menu, select Extensions....
2 Click on the box next to ‘Cad Reader’ (if not already turned on), then click
OK.
This enables the CAD Reader extension, so ArcView GIS can now display DXF
and DWG vector files.
3 Click the Add Theme
button (or select View > Add Theme).
The files in the ‘shared_data’ directory should be displayed.
4 Open the ‘examples\data_types\autocad_dxf’ folder.
5 On the Add Theme dialog, select ‘Feature Data Source’ from the ‘Data
Source Types’ list.
6 Double-click on the file ‘roads.dxf.’
7 In the ‘View3’ window turn on the ‘Roads.dxf’ theme.
ArcView GIS displays a vector roads coverage over the airphoto.
8 If desired, select ‘roads.dxf’ theme and change the vector color and line
size to make them more visible. (Select Theme > Edit Legend, then
double-click on the vector in the Symbol column).
9 Close the views by clicking the Close
button on the view windows.
These simple examples show how you can use the power of ER Mapper algorithms
showing various “views” of your image data, and display them directly inside
ArcView GIS.
Open a URL file
The ER Mapper extension enables you to open an ECW compressed image, served
via an ER Mapper Image Web Server, inside arcview by specifying its URL. You
can then zoom into and roam over this image in real time. The Image Web Server
sends the compressed image blocks as they are requested.
The extension includes the facility to store image URLs in a ‘Favorites’ list so that
they can easily be accessed in later ArcView® sessions. You can also select URLs
from a ‘History’ list that displays the last 20 URLs requested.
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In order for you to do these exercises, the PC in which ArcView is installed must
have access to an Image Web Server over the Internet or private intranet. In this
example we will use the public ‘www.earthetc.com’ web site.
1 On the Project window, click New to open a new View window. (It should be
titled ‘View1’.)
2 Click the Add ECW Image Theme from an Image Web Server URL
button (or select View > Add URL Theme).
This should open the Image Theme URL dialog box.
3 Enter the following URL in the URL: field.
ecwp://www.earthetc.com/images/world/gtopo30.ecw
This URL will access the gtopo30.ecw compressed image file at the Earth
Resource Mapping www.earthetc.com web site. The protocol to be used is ECWP
(Enhanced Compression Wavelet Protocol).
Note: This step requires your PC to have Internet Access. If you are accessing another
Image Web Server on a local network, you must change the URL accordingly.
The 1 Km resolution image of the world was created by using the ER Mapper
Image Display and Mosaic Wizard to mosaic 30 gtopo DTMs (Digital Terrain
Maps). The resultant 2.8GB image was then compressed to 50 MB using ECW
compression.
4 Click on the OK button.
The image will be loaded as theme via the Internet. If you have a slow connection
to the Internet this step could take a few minutes. If your PC is not able to access
the www.earthetc.com web site, it will display an error message.
5 In the ‘View1’ window turn on the ‘Gtopo30.url’ theme.
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ArcView GIS displays the world image.
Turn on the theme
6 In the ‘View1’ window, select the ‘Gtopo30.URL’ theme and then select
Edit > Delete Themes to remove the theme. Answer Yes to the Delete
Themes query.
7 Click the Add ECW Image Theme
button (or select View > Add URL
Theme) to reopen the Image Theme URL dialog box.
The URL: field should now be blank.
8 From the History: list select the ‘ecwp://www/earthetc.com/images/world/
gtopo30.ecw’ entry.
The History: list contains the last 20 URLs entered. This saves you from having to
type in the full URL to re-open a recently accessed image.
The URL: field should now contain the URL that you selected from the History:
list. If you were to click on the OK button, it would re-load the image as a theme in
the ‘View1’ window.
9 Click on the Add to Favorites button to open the Add to Favorites dialog
box.
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This box allows you to select a directory and file name to store URLs that you are
likely to access again. The file names all have a .url extension.
You should note that there is already a ‘gtopo30.url’ entry in the
‘arcview\averm\urls’ directory. The ER Mapper extension automatically creates
these files in the default directory whenever you access a URL. The Add to
Favorites facility is really only required if you want to save the URL to another
directory and/or under another name.
10 Select the default directory, which should be ‘ARCVIEW\averm\urls’.
11 Enter World_<your initials>.url in the File Name: field and click on the
OK button to return to the Image Theme URL dialog box.
12 Click on the Open from Favorites button.
This opens the Open From Favorites dialog box
Automatically
created entry
Default favorites
directory
Your entry
13 Select the ‘arcview\averm\urls’ directory if it is not already selected.
14 Select the ‘World_<your initials>.url’ file which you previously added. There
should also be ‘gtopo30.url file’ that was automatically created by the
ER Mapper extension.
15 Click on the OK button to return to the Image Theme URL dialog.
The URL: field should now contain he full URL .
16 Click on the OK button.
The image will be loaded as theme via the Internet. If you have a slow connection
to the Internet this step could take a few minutes. If your PC is not able to access
the www.earthetc.com web site, it will display an error message.
You should also note that the theme name is now the same as that you entered for
the ‘Favorites’ file.
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17 In the ‘View1’ window turn on the ‘World_<your initials>.url’ theme.
The same world image will open with the new theme name.
Zoom, pan and measure the image
1 Click the Zoom In
tool, then drag a box over the central part of the
image to zoom into it.
2 Click on the Refresh View
Tip:
button to improve the image resolution.
If you are connected to the Internet via a slow link, you may have to click on the
Refresh View button a number of times to get the best resolution. This is because
ArcView® may display the image before it is fully downloaded from the server.
The Refresh View button reloads the image with all new information that has
been cached on the PC.
3 Click the Pan
tool, then drag the image to view adjacent areas.
4 Click on the Refresh View
5 Click the Measure
area.
button to improve the image resolution.
tool, then drag a line to view distances across an
The line length appears in the lower-left corner of the ArcView GIS dialog.
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Close ArcView GIS
1 If desired, save your views as an ArcView project using File > Save Project
As....
2 Close ArcView GIS by clicking the Close
window or selecting File > Exit.
What you
learned...
316
button on the application
After completing these exercises, you know how to perform the following tasks in
ArcView GIS using the ER Mapper Imagery Extension:
•
Enable the ER Mapper Imagery Extension after starting ArcView GIS
•
Display an ER Mapper image file (.ers) as an Image Data Source
•
Display an ER Mapper algorithm file (.alg) as an Image Data Source
•
Display a vector theme on an ER Mapper image
•
Display an ER Mapper URL file (.ecw) as an Image Data Source.
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19
MapInfo Users
This chapter explains how to use the free MapImagery plug-in for MapInfo
software to view ER Mapper imagery and algorithm files. (The free MapImagery
plug-in is developed by GID Australia.) It also explains how to obtain and install
the plug-in, and the additional imaging capabilities MapInfo users can gain by
using the plug-in in conjunction with ER Mapper.
Note: You must have a licensed copy of MapInfo version 4.5 or greater to install and run
the MapImagery plug-in. You do not need to have a copy of ER Mapper installed,
but this is recommended to gain access to sample ER Mapper imagery and
algorithms used in the following tutorial. (You can order the free ER Mapper
installation CD-ROM from www.ermapper.com.)
About the MapImagery plug-in for MapInfo
As imagery data sources become more important for GIS applications, the need to
efficiently display, process and enhance large image files also becomes more
important. GID Australia provides a plug-in that lets MapInfo users directly display
ER Mapper imagery and algorithms. This plug-in uses the ER Mapper processing
engine to display imagery within MapInfo.
Using the plug-ins, MapInfo users can choose from three levels of imagery support:
•
Level 1 (using the free MapImagery plug-in)–By installing the free MapImagery
plug-in, MapInfo users can directly display ER Mapper imagery and algorithms
from within MapInfo. You can also use the plug-in to display other imagery formats
directly supported by ER Mapper such as GeoTIFF, BMP, GeoSPOT and others.
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•
Level 2 (using the commercial MapImagery plug-in)–By installing the
commercial version of MapImagery plug-in, MapInfo users add advanced image
processing capabilities to MapInfo. These include contrast enhancement,
convolution filtering, image mathematics functions, color lookup tables, and much
more. The commercial version can also create ER Mapper algorithms. For
information on the commercial version, contact GID Australia at their web site at
www.gid.com. (GID Australia also makes other ER Mapper and MapInfo tools. See
their website for information.)
•
Level 3 (using the free MapImagery plug-in with a licensed copy of
ER Mapper)–By purchasing a license for ER Mapper, MapInfo users can access
the full range of high-level ER Mapper image processing functions, and display the
images within MapInfo using the free or commercial MapImagery plug-in.
ER Mapper provides functions for easily creating seamless, color balanced mosaics
of many large image files such as airphotos. It also provides advanced image
processing functions such as orthorectification, image reprojection, multispectral
classification, color shaded reliefs, raster to vector conversion, image merging/
fusion, support for over 100 imagery formats and over 200 hardcopy printing
devices, and much more.
How to obtain the free MapImagery plug-in
You can obtain the free MapImagery plug-in from three sources:
•
The GID Australia web site–GID Australia regularly updates the MapImagery
plug-in and posts the latest version on their web site at www.gid.com. Navigate to
the “products and services” area and download the free MapImagery plug-in.
•
The ER Mapper web site–You can download the plug-in from the ER Mapper web
site at www.ermapper.com. Navigate to the “free software” area and download the
MapInfo plug-in.
•
The ER Mapper installation CD-ROM–The plug-in can be installed as a separate
component from the ER Mapper installation CD-ROM. (Note that this may not be
the latest version. Check the GID Australia web site for the latest update.)
Hands-on exercises
These exercises show you how to use the free MapImagery plug-in for MapInfo.
What you will
learn...
318
After completing these exercises, you will know how to perform the following
tasks in MapInfo using the free MapImagery plug-in:
•
Display an ER Mapper image file (.ers) as a MapInfo table
•
Display an ER Mapper algorithm file (.alg) as MapInfo table
•
Overlay MapInfo vector and tabular table data on an ER Mapper image
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Chapter 19 MapInfo Users ● 1: Open an ER Mapper image file
•
Before you
begin...
Choose MapImagery setup options to control image display and printing
Before beginning these exercises, you must have installed MapInfo version 4.5 or
higher and the free version of the MapImagery plug-in on your system.
Note: These exercises use sample ER Mapper imagery and algorithm files from the
ER Mapper installation CD-ROM. You may also follow the general procedures
using your own ER Mapper imagery (.ers) or algorithm (.alg) files.
1: Open an ER Mapper image file
Objectives
Learn to use the MapImagery plug-in to display ER Mapper imagery (.ers) files
and to zoom, pan and measure distances on the image.
Note: You can use the following procedure to open any image formats supported by
MapImagery, including TIFF, Windows BMP, JPEG, SPOTView, ESRI BIL, and
others. (Additional formats are added periodically, so make sure you are using the
latest version of MapImagery.)
Start MapInfo
1 Start the MapInfo software on your system.
2 If the Quick Start dialog appears, click Cancel on it.
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In the MapInfo application window, you should see the MapImagery plug-in
enabled as both a floating toolbar and menu:
MapImagery menu and toolbar
3 Click the Maximize
button in the upper-right corner of the MapInfo
application window (if it is not already maximized)
MapInfo expands to fill your desktop.
Open an ER Mapper-format (.ers) image file
1 Click the Open Image
button on the MapImagery toolbar (or select
MapImagery > Open Image).
Open Image
The option lets you open several types of imagery files directly inside MapInfo.
2 On the Open Image Files dialog, open the ‘Files of Type’ list.
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A list of all the supported imagery formats displays. You can open ER Mapper
imagery (.ers) and algorithm (.alg) files, as well as TIFF and BMP and compressed
formats such as ER Mapper’s compressed wavelet (.ecw), and JPEG. (Make sure
the ‘All Image Files’ option is selected when closing the list.)
3 Double-click on the folder where ER Mapper is installed. Then open the
directory ‘examples\Applications\Land_Information.’
A list of ER Mapper imagery (.ers) and algorithm (.alg) files appears.
4 Scroll down to the bottom, then double-click on the file
‘SPOT_XS_07Aug88.ers.’
5 If you see a message asking to overwrite the existing .alg file, click Yes.
The Choose Algorithm Style dialog appears. This lets you select how you want
MapImagery to display the image.
6 Select the ‘Automatic contrast stretching’ option, then click OK.
7 If you see a message asking to overwrite the previous .tab file, click Yes.
The MapImagery Projection dialog appears.
8 Select the correct MapInfo projection items (as follows), then click OK:
•
MapInfo Category–>Universal Transverse Mercator (NAD27 for US)
•
MapInfo Category Members–>UTM Zone 11 (NAD27 for US)
•
MapInfo Units–meters
MapImagery displays a SPOT XS color satellite image of the San Diego, California
area in a new map window. This is a 3-band color infrared image, so vegetated
areas appear in red tones. The spatial resolution (pixel size) is 20 meters.
Note: When you open image or algorithm file, MapImagery creates a MapInfo table (.tab)
file to allow correct coordinates and georeferencing. You may be prompted to
overwrite this file; see “Table (.tab) files created by MapImagery” in part 3 in this
chapter for details on when and why to do this.
Zoom, pan and measure the image
1 Click the Zoom-in
button on the Main toolbar, then drag a box around
the central part of the SPOT image to zoom in on it.
2 Click the Grabber
tool, then drag the image to view adjacent areas.
3 Click the Ruler
tool, then drag a line between two points on the image
and double-click to end it.
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The distance along the line is displayed in the pop-up Ruler dialog.
4 Select Map > View Entire Layer, then click OK on the pop-up dialog.
The image zooms out to the full extents of the SPOT satellite image.
View geographic coordinates on the image
1 Select Map > Options.
2 On the Map Options dialog, select degrees or meters for ‘Coordinate
Units’ (whichever you prefer).
3 Under ‘Display in Status Bar,’ click ‘Cursor Location.’ Then click OK.
4 Move the cursor around inside the satellite image.
Geographic coordinates appear in the Status Bar (lower-left area). The coordinates
are in Latitude/Longitude (if you chose degrees) or meters of Eastings and
Northings in the UTM projection (if you chose meters).
5 Select File > Close All to close all current tables (in case any others were
also open).
2: Open ER Mapper algorithm files
Objectives
Learn to use the MapImagery plug-in to display ER Mapper algorithm (.alg) files,
and to add several images as different layers in your map.
Open an ER Mapper algorithm (.alg) file
In ER Mapper, an algorithm is a list of processing steps or instructions ER Mapper
uses to transform a raw imagery file into a final, enhanced image on your screen or
printer. Algorithms let you define a “view” into your data that you can save, reload,
and modify at any time. By using the MapImagery plug-in, you can display
ER Mapper algorithms just like any other imagery file.
Tip:
You can create algorithm files with ER Mapper or with the commercial
version of the MapImagery plug-in. You only need the free MapImagery plug-into
view algorithm files in MapInfo.
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1 Click the Open Algorithm
button on the MapImagery toolbar (or
select MapImagery > Open Algorithm).
Open Algorithm
The files in the ‘Land_Information’ directory should be displayed.
2 Backup one directory (to ‘Applications’). Then double-click on the ‘Airphoto’
folder, then double-click on the ‘3_balancing’ folder.
A list of ER Mapper imagery (.ers) and algorithm (.alg) files appears.
3 Double-click on the ‘San_Diego_Airphoto_34_36_Balanced_Mosaic.ers’
file.
4 If you see a message asking to overwrite the previous .tab file, click Yes.
5 The correct MapInfo projection parameters are displayed, then click OK.
MapImagery displays a mosaic of two orthorectified color airphotos of the
downtown San Diego, California area. This image is created from an ER Mapper
algorithm, so it has several processing enhancements applied to the two airphoto
imagery (.ers) files used as input:
•
brightness and color variations within each image are normalized to remove
“hotspots” or light-to-dark variations across each photo
•
the contrast and brightness of the two normalized images are then balanced to each
other ensure uniform color and brightness across the mosaic
•
the seam between the two images is feathered to ensure a smooth transition between
the two images and make the mosaic truly “seamless”
6 Click the Zoom-in
button on the Main toolbar, then drag a box around
the central area of the airphoto mosaic.
MapImagery applies the algorithm processing to the airphotos, then zooms in to
display your area of interest.
7 Click the Grabber
tool, then drag the image to view adjacent areas.
MapImagery applies the algorithm processing, then pans to display the adjacent
area.
8 Select File > Close All to close all current tables (in case any others were
also open).
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This example shows how you can access the power of ER Mapper algorithms to
apply complex image enhancements and display them directly within MapInfo.
(Each one of these airphotos is over 30MB in size.) This example uses only two
airphotos, but you could just as easily display a mosaic algorithm containing 100’s
of megabytes (even gigabytes) of airphoto images.
Note: When you have displayed an image and selected the projection information in
MapInfo, MapImagery remembers this in the future. See “Choosing map projection
information” in part 3 in this chapter for more information on how and when to
select projections.
Set the option to add multiple images to the current mapper
For this next example, you will add several images as layers in the same mapper
window. MapImagery has setup options to make this easier.
1 Click the MapImagery Options
button (on the MapImagery toolbar),
or select MapImagery > MapImagery Options.
2 Click the General tab. Under ‘When Opening an Algorithm Table’ select the
‘Add to Current Mapper’ option. Click OK.
This tells MapImagery to add new images to the same mapper, rather than open a
new mapper each time.
Open a merged satellite image algorithm
1 Click the Open Algorithm
button on the MapImagery toolbar (or
select MapImagery > Open Algorithm).
The files in the ‘3_Balancing’ directory should be displayed.
2 Backup to the ‘examples’ directory. Double-click on the
‘Functions_and_Features’ folder, then double-click on the ‘Data_Fusion’
folder.
A list of ER Mapper algorithm (.alg) files appears. These algorithms all show
different ways of merging (or “fusing”) two different images into one.
3 Double-click on the file ‘Brovey_Transform.alg.’
4 The correct MapInfo projection parameters are displayed, then click OK.
MapImagery displays a color image of the San Diego, California area. This is a
merge of a Landsat TM satellite image (bands 5, 4 and 2) and a SPOT
Panchromatic satellite image. By merging the two types of data, you get the high
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spatial detail provided by the SPOT Pan image (10-meter resolution) with the
multispectral color information provided by the Landsat TM image (seven bands at
30-meter resolution).
The Brovey Transform is a mathematical way of combining the two images that
also greatly enhances the color. Merging or fusion techniques like this are used to
combine the strengths of different satellite sensors and create detailed, up-to-date
views of the earth’s surface.
5 Use the Zoom-in
tool to zoom into the image. Then use the Grabber
tool to pan around inside it.
MapImagery applies the algorithm processing to merge the two image files, then
displays your new area of interest.
The image shows a high resolution, color-enhanced view of the area. As with the
airphoto mosaic, the ER Mapper algorithm creates this image interactively from the
two separate Landsat and SPOT satellite imagery files. (The Brovey Transform
technique usually requires up to three intermediate image files to be created when
using traditional imaging software, but ER Mapper performs the processing in real
time from the two source images without creating intermediate files.)
6 Select Map > View Entire Layer, then click OK on the pop-up dialog.
The image zooms out to the full extents of the merged satellite image.
Add a second image (algorithm) showing thematic land cover
1 Click the Open Algorithm
button on the MapImagery toolbar (or
select MapImagery > Open Algorithm).
The files in the ‘Data_Fusion’ directory should be displayed.
2 Open the ‘examples\Functions_and_Features\Classification_Display’ folder.
3 Double-click on the file ‘ISOCLASS_Classification.alg.’
4 The correct MapInfo projection parameters are displayed, then click OK.
MapImagery displays a thematic color image of the same area of San Diego.
Different colors correspond to different types of landuse in the area. This image
was created from a 1985 Landsat TM satellite image using ER Mapper’s
ISOCLASS unsupervised classification feature. Classification groups pixels with
similar spectral values into classes that can represent different types of landuse or
land cover.
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Add a third image (algorithm) showing topography
1 Click the Open Algorithm
button on the MapImagery toolbar (or
select MapImagery > Open Algorithm).
The files in the ‘Classification_Display’ directory should be displayed.
2 Open the ‘examples\Data_Types\Digital_Elevation’ folder.
A list of ER Mapper algorithm (.alg) files appears. These algorithms all show
different ways displaying and processing digital elevation model (DEM) data files.
3 Double-click on the file ‘Colordrape.alg.’
4 The correct MapInfo projection parameters are displayed, then click OK.
MapImagery displays a color shaded relief (or “colordrape”) image of the same
area of San Diego. Colors represent elevation (reds are highest) and the shading
effect highlights topographic features such as hills and valleys. This image is
illuminated from the northeast, so shadows appear on the southwest side of terrain
features. ER Mapper has a built-in “realtime shading” feature that lets you
interactively change the shading parameters without creating output files.
View the three images (layers) in the mapper
1 Click the Layer Control
Layer Control).
button on the Main toolbar (or select Map >
2 In the Layer Control dialog, turn off the Visible checkboxes for the
‘Colordrape’ and ISOCLASS_classification’ layers, then click OK.
Turn off Visible
checkbox for layers
MapImagery redisplays the Brovey Transform algorithm.
3 If desired, repeat step 2 to view other images (turn on only the one you
want, then click OK).
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4 If desired, save your workspace using File > Save Workspace.
5 Select File > Close All to close any open tables.
3: Overlay MapInfo vector data
Objectives
Learn to overlay MapInfo vector and point table data on an ER Mapper algorithm
image. In this case, you will display a world shaded relief image generated by an
ER Mapper algorithm, then overlay MapInfo data of a Lat/Long grid, world
capitals, and country borders.
Open an ER Mapper world topography algorithm
1 Click the Open Algorithm
button on the MapImagery toolbar (or
select MapImagery > Open Algorithm).
2 Backup to the ‘examples’ folder, open the ‘applications’ folder, then open the
‘World_Topography’ folder.
A list of ER Mapper imagery (.ers) and algorithm (.alg) files appears.
3 Double-click on the ‘World_Topography.alg’ file.
4 If you see a message asking to overwrite the previous .tab file, click Yes.
5 Select the correct MapInfo projection items (as follows), then click OK:
•
MapInfo Category–>Longitude / Latitude
•
MapInfo Category Members–>Longitude / Latitude
•
MapInfo Units–degrees
MapImagery displays a color shade relief image (a “colordrape”) of the world.
Colors of the land areas represent elevation (magenta are the highest, red are the
lowest). Ocean areas are colored blue, and bathymetric features such as mid-ocean
ridges are shown by the shading effect.
Note: When displaying data that is in a Longitude Latitude coordinate system, it is
important to select ‘degrees’ as the map projection units. This lets you overlay any
other data that is also stored in degrees.
View Longitude Latitude coordinates on the image
1 Select Map > Options.
2 On the Map Options dialog, select degrees for ‘Coordinate Units.’
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3 Under ‘Display in Status Bar,’ click ‘Cursor Location.’ Then click OK.
4 Move the cursor around inside the satellite image.
Longitude Latitude coordinates appear in the Status Bar. (Negative Longitudes
indicate the western hemisphere, and negative Latitudes indicate the southern
hemisphere.)
Overlay a Longitude Latitude coordinate grid
1 Select File > Open Table.
2 On the Map Options dialog, open the ‘WORLD’ directory (under the
MapInfo ‘Data’ directory).
3 Double-click on the ‘GRID15.TAB’ file.
MapInfo overlays a Longitude Latitude grid (graticule) with a 15-minute grid
spacing.
Overlay a table of world capital cities
1 Select File > Open Table.
2 Double-click on the ‘WORLDCAP.TAB’ file.
MapInfo overlays the locations of world capital cities.
3 Click the Layer Control
button on the Main toolbar (or select Map >
Layer Control). Turn on auto labelling, then click OK.
Turn on
Auto Label
MapInfo redisplays the world map with labels (city names) plotted next to the
symbols. (If desired, you can make the labels bigger, change fonts, and so on by
selecting Layer Control again and clicking Labels...).
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Overlay a table of vector country borders
1 Select File > Open Table.
2 Double-click on the ‘WORLD.TAB’ file.
MapInfo overlays the borders of countries on the world map.
Turn off the GRID15 and WORLDCAP layers
1 Click the Layer Control
button again. Turn off the ‘GRID15’ and
‘WORLDCAP’ layers, make the ‘WORLD’ layer editable, then click OK.
Turn off display
of GRID15 and
WORLDCAP
Make WORLD
layer editable
MapInfo redisplays the map without the grid and capital cities layers.
Make the Africa country border polygons transparent
1 Click the Marquee Select
button on the Main toolbar, then drag a
selection box around the continent of Africa.
MapInfo selects all the polygons in your selection marquee.
2 Click the Region Style
> Region Style).
button on the Draw toolbar (or select Options
3 On the Region Style dialog, select the ‘Pattern’ of ‘None,’ then click OK.
The selected region polygons redisplay without the fill pattern, so you can see the
country borders in relation to the ER Mapper world topography image.
4 Click Zoom-in
on the Main toolbar, then drag a box around the African
continent to zoom in on it.
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Query the country data or go to other areas of the world
1 If desired, use the MapInfo query tools to get information about the
countries, or follow the same steps as above to make country borders for
other regions transparent.
2 (Optional.) Save your workspace using File > Save Workspace.
4: MapImagery settings and options
Objectives
Learn to understand the way MapImagery handles and displays imagery, and how
to setup default options to control the way images are displayed and printed in
MapInfo. (There are no exercises here, only information.)
Table (.tab) files created by MapImagery
When you open an ER Mapper imagery or algorithm file (or any other supported
format), MapImagery automatically creates a MapInfo table (.tab) file for the
image. The table file contains information on the map projection, image extents,
viewing resolution, and other information MapInfo needs to properly display the
image. When you open an image or algorithm file that was already opened in the
past, MapImagery prompts you to overwrite the previously created table file in case
you have changed any parameters since then.
You would want to overwrite the existing table file in the following cases:
•
You selected the wrong map projection information the first time. Click Yes to
overwrite the existing table file for the image, and select the correct projection
information for the future.
•
You change the ‘Supersampling Factor’ on the MapImagery Options dialog’s
Supersampling tab. This option lets you manipulate the quality of images within
MapInfo, but is also tied to the image extents and coordinates saved in the table file.
If you change the supersampling factor, you must regenerate the table files for all
imagery files you opened in the past. Click Yes to overwrite the existing table file
for the image to update the supersampling setting. (If you do not overwrite the
existing table file, your image will display but the map coordinates will be wrong,
so this is very important.)
Algorithm (.alg) files created by MapImagery
When you open an ER Mapper imagery (.ers) or other supported image file,
MapImagery automatically creates an ER Mapper-format algorithm file for the
image (in addition to a MapInfo table file). The algorithm file tells MapImagery
how to display the image file, and is independent from the image file itself.
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When you open an image file that was already opened in the past, MapImagery
prompts you to overwrite the previously created algorithm file. You should do this
if you want to change the contrast enhancement option you selected the first time
you opened the image. Otherwise, you do not need to overwrite it.
Choosing map projection information
When you open an ER Mapper or other image file for the first time, or when you
choose to overwrite an existing table (.tab) file, you are presented with MapInfo
projection options. These options let you choose the correct map projection and
coordinate units, and these are important to make sure that georeferenced images
display with correct coordinates in MapInfo.
Since the image often originated in ER Mapper, it usually has georeferencing
information attached to it (stored in the .ers header file). You need to match the
ER Mapper projection information to the equivalent information in MapInfo. Once
you do this one time for a given projection type, MapImagery remembers this
setting and will automatically set the MapInfo defaults for you when you open
another image that has the same ER Mapper projection parameters.
To match the ER Mapper projection information to the MapInfo equivalent,
examine the ER Mapper information at the top, then make the appropriate
selections from MapInfo projection database:
ER Mapper datum,
projection, units
Select corresponding
MapInfo Category,
Member and Units
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The Supersampling setting
When you open an ER Mapper or other image file, MapImagery processes and
displays the image data at a predefined resolution. This is called supersampling,
and is controlled by the ‘Supersampling Factor’ on the MapImagery Options
dialog’s Supersampling tab. For example, if you set supersampling to 8, then an
8x8 pixel area is displayed for every underlying pixel.
You should set the supersampling factor according to these guidelines:
•
Use lower values to speed display of very large images, or mosaic algorithms
containing many images. Lower values may not produce optimal hardcopy prints
however.
•
Use higher settings to improve detail in on the screen when smoothing is enabled in
the ER Mapper algorithm, and when hardcopy printing from MapInfo.
Contrast enhancement options
When you open an ER Mapper imagery (.ers) file and are prompted to create an
algorithm for it, clicking Yes displays the Choose Algorithm Style dialog. This
dialog lets you choose how contrast will be adjusted to improve the image
presentation:
•
Create an algorithm with No contrast stretching–This displays the image without
enhancing the contrast. Use this option if you wish to view the image without
enhancement or if your image is already contrast enhanced. Non-photographic
images like digital terrain models (DEMs) may look better when displayed this way,
or may look better with contrast stretching.
•
Create an algorithm with Automatic contrast stretching–This displays the image
with a linear contrast enhancement to improve color and brightness. Use this option
for images that are not already contrast enhanced (like satellite images) or if your
images look too dark or light or lack contrast using the no stretching option.
The type of contrast enhancement applied is a linear contrast stretch that “clips” (or
saturates) a certain percentage of brightest and darkest pixels at the high and low
ends of the image histogram. The amount of clipping (percentage) is set in the
MapImagery Options dialog’s Algorithm Generation tab. A 99% clip
applies a mild contrast enhancement that look good on many types of images. If the
image still lacks contrast, choose 97.5. (The smaller the percentage the more
contrast, but experiment for best results.)
Note: The algorithm file contains the contrast enhancement settings, so the setting you
choose is automatically applied to all images you open (if you choose to overwrite
an existing algorithm file). If you have a problem image, try smaller percent values
for that image, then set the default back to 99% so it is used in the future.
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Close MapInfo
1 Close MapInfo by clicking the Close
or selecting File > Exit.
What you
learned...
button on the application window
After completing these exercises, you know how to perform the following tasks in
MapInfo using the free MapImagery plug-in:
•
Display an ER Mapper image file (.ers) as a MapInfo table file
•
Display an ER Mapper algorithm file (.alg) as MapInfo table file
•
Overlay MapInfo vector and tabular table data on an ER Mapper image
•
Choose MapImagery setup options to control image display and printing
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20
Autodesk World
Users
This chapter explains how to use the capabilities of the Autodesk World software to
display ER Mapper imagery and algorithm files as backdrops. This chapter covers
steps similar to those described in the Autodesk World software documentation and
help system.
Note: You must have a licensed copy of Autodesk World 2.0 to run this tutorial. You do
not need to have a copy of ER Mapper installed, but this is recommended to gain
access to sample ER Mapper imagery and algorithms used in the following tutorial.
(You can order the free ER Mapper installation CD-ROM from
www.ermapper.com.)
About Autodesk World’s ER Mapper image viewing engine
As imagery data sources become more important for GIS applications, the need to
efficiently process, enhance and display large image files also becomes more
important. Many projects require the analysis of vector GIS drawing data by
presenting it over image backdrops that show a “real world” perspective. For
example, you gain a better understanding of parcel ownership, tax zones, zip codes,
and many other vector entities by overlaying them on an airphoto showing landuse
and buildings.
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Autodesk World incorporates the ER Mapper viewing engine, which lets you
incorporate nearly any type of image data into your projects. These include aerial
photographs, satellite images, digital elevation (topography) images and many
more image types.
By incorporating the ER Mapper image viewing engine, Autodesk World users are
not restricted by limited image handling capabilities as are some other GIS
products. You can directly display ER Mapper imagery and algorithms, and image
formats with location information such as GeoTIFF, ESRI/GeoSPOT HDR, and
others. In addition, you can experience the full power of ER Mapper algorithms
from within Autodesk World.
Using Autodesk World with ER Mapper
By using Autodesk World in conjunction with a copy of the ER Mapper software,
you gain access to the extensive capabilities of this powerful integrated mapping
and image processing product, including:
•
Import and display over 100 different image formats
•
Use advanced image processing functions such as contrast enhancement,
multispectral classification, vegetation indexes, color shaded reliefs, filtering,
merging images, and many others.
•
Directly read TIFF, GeoTIFF, Windows BMP, ER Mapper images and algorithms,
ESRI BIL, SPOTView and Universal Data Format (UDF) imagery without the need
for import or conversion
•
Easily view the entire project area in one image–no limits on image file sizes
•
Geocode, orthorectify or reproject imagery easily to precisely register with GIS
vector drawing data
•
Automatically display, mosaic and color balance numerous images
•
Combine imagery, vector and tabular data from any number of sources
•
Create and edit vector data over imagery backdrops, and highlight features of
interest and save them as vectors with ER Mapper’s raster to vector conversion tools
Hands-on exercises
These exercises show you how to use the ER Mapper image display capabilities
within Autodesk World.
What you will
learn...
After completing these exercises, you will know how to perform the following
tasks in Autodesk World:
•
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Chapter 20 Autodesk World Users ● 1: Inserting an ER Mapper image
Before you
begin...
•
Enhance the image contrast and apply image smoothing
•
Choose equivalent coordinate systems in Autodesk World and ER Mapper
•
Insert an ER Mapper smart data algorithm into an Autodesk World drawing
•
Stack and change the order of multiple images in a drawing
•
Combine image and vector drawing data in a project
Before beginning these exercises, you must have installed Autodesk World
version 2.0 or higher on your system. These exercises use sample ER Mapper
imagery and algorithm files from the ER Mapper installation CD-ROM. You may
also follow the general procedures using your own ER Mapper imagery (.ers) or
algorithm (.alg) files.
1: Inserting an ER Mapper image
Objectives
Learn to insert ER Mapper imagery (.ers) files into an Autodesk World drawing.
(You can also use the following procedure to open any image formats directly
supported by ER Mapper, including TIFF and GeoTIFF, Windows BMP,
SPOTView, ESRI BIL, and others.)
The ER Mapper imagery (.ers) format stores image data in its “raw” form. That is,
the imagery may not be processed or enhanced for best presentation. When you
insert an ER Mapper image, Autodesk World gives you options to enhance the
imagery as it is loaded and displayed.
Start Autodesk World
1 Start the Autodesk World software on your system.
2 Click the Maximize
button in the upper-right corner of the Autodesk
World application window (if it is not already maximized).
Autodesk World expands to fill your desktop. You should start with a new project.
3 If you do not already have a new (empty) project open, start one by
choosing File > New, then clicking Blank Template.
4 If the Display Manager window is open, close it.
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Set the coordinate system for the new project
All projects have an associated coordinate system. If you are beginning with an
ER Mapper image that has location information as your “basemap,” you should
choose the same coordinate system as the image for your project.
1 Choose File > Properties.
2 Click the Coordinate System tab, then click Change....
3 On the Project Detail dialog, select UTM27-11 from the Coordinate
System list.
This selection specifies a coordinate system using the NAD27 datum and the
Universal Transverse Mercator (UTM) map projection (zone 11 in the northern
hemisphere). The coordinate units are meters, so locations are defined in meters of
Eastings and Northings.
4 Click OK on the Project Detail dialog, then click OK on the Project
Properties dialog.
This coordinate system is now assigned to your project, and is the same one used by
the ER Mapper images you will use in the upcoming examples.
Insert an ER Mapper-format (.ers) image into the drawing
1 Choose Insert > ER Mapper Image.
2 On the Insert ER Mapper Image dialog, click the Image tab, then click
Browse.
3 Double-click on the folder where ER Mapper is installed, then open the
‘examples/Applications/Airphoto/1_Geocoding’ folder.
A list of ER Mapper algorithm (.alg) files appears.
4 Turn off the ‘Bilinear Smoothing’ and ‘Contrast Stretching’ options. (These
will be explained later).
5 Click on the ‘Files of Type’ list to view the different image formats.
You can insert ER Mapper algorithms (.alg) and datasets (.ers), as well as TIFF,
BMP, ARC/INFO-GeoSPOT HDR, and others.
6 From the ‘Files of Type’ list, select Datasets (*.ers).
7 Double-click on the file ‘San_Diego_Airphoto_34_rectified.ers.’
8 Click the Zoom All
button or choose View > Zoom All.
Autodesk World displays a color aerial photograph of the downtown San Diego,
California area. This image has been rectified to the NAD27 datum and UTM zone
11 map projection, so it has geographic location information (true earth
coordinates).
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Zoom in to a small area to see the pixel resolution
1 Click the Zoom Window
button (or choose View > Zoom Window),
then drag a very small box over part of the photo to zoom into it.
If needed, do this again until you can see the small square areas that comprise the
digital image. These squares are called pixels (for picture elements), and are
roughly equivalent to the smallest object you can see in the photo. In this image,
each pixel is about 1 meter in diameter, which is termed “1-meter resolution.”
Reload the image with smoothing and contrast enhancement
1 Choose Insert > ER Mapper Image.
2 This time turn on the ‘Bilinear Smoothing’ and ‘Contrast Stretching’ options.
3 From the ‘Files of Type’ list, select Datasets (*.ers).
4 Click Browse, then double-click on the file
‘San_Diego_Airphoto_34_rectified.ers’ again to reload it.
The airphoto image redisplays with improved contrast and a “smoother”
appearance.
•
Bilinear Smoothing improves the display of zoomed images or large hardcopy
prints by averaging the pixel values to remove the “blocky” look you saw previously
when smoothing was not turned on. (You only see the effect of smoothing when you
zoom into the pixel level.)
•
Contrast Stretching generally improves the image color and presentation by
increasing contrast between the light and dark areas. This option is recommended
when inserting most image files, otherwise they may lack contrast or look too dark
or light.
Zoom in and out in the image
1 Click the Zoom All
button or choose View > Zoom All.
The image zooms out to display the full extents of the airphoto.
2 Click the Zoom Window
button (or choose View > Zoom Window),
then drag a box over the central part of the photo to zoom into it.
3 Click the Zoom In
or Zoom Out
to zoom in or out by fixed amounts.
buttons, then click on the image
4 When finished, click the Zoom All
to zoom out to the full image extents.
button or choose View > Zoom All
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5 Once again, click Zoom Window
of the photo to zoom into it.
, then drag a box over the central part
Pan (scroll) the image
1 Click the Pan 2 Points
button (or choose View > Pan). Click on one
point in the photo, then click on a second point.
The image pans (scrolls) in the direction and distance you defined by your two
points. This is one way to view adjacent areas of an image.
2 Drag the scroll bars on the right or lower areas of the project window.
The image pans in the direction you drag the scroll bar.
View geographic coordinates on the image
1 Choose Tools > Format Options.
2 Click the Coordinate tab, select Latitude Longitude from the ‘Display
Type’ list, then click OK.
3 Point to various locations in the image.
The Latitude Longitude coordinates of the current cursor location appear in the
status bar. (The format is decimal degrees, and negative longitudes indicate the
western hemisphere.)
4 Choose Tools > Format Options again.
5 Click the Units tab, then select m from the ‘User Unit’ list.
6 Click the Coordinate tab, select Projection Coordinate from the ‘Display
Type’ list, then click OK.
7 Point to various locations in the image.
The UTM map projection coordinates appear in the status bar. (The format is
meters of Northings and Eastings in UTM zone 11.)
Close the project
1 Choose File > Close.
When asked to save the contents or save changes, click No.
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2: Inserting multiple coregistered images
Objectives
Learn to insert ER Mapper smart data algorithm (.alg) files into an Autodesk
World drawing. Also learn to “stack” multiple images covering the same
geographic area, and to turn images on/off and move them to the top of the
display.
An ER Mapper algorithm is a list of processing steps or instructions ER Mapper
uses to transform a raw image file into a final, enhanced image on your screen or
printer. An algorithm does not contain the actual image data, but only stores
references to it. (The actual image data is stored in ERS or other files.) When you
insert an ER Mapper algorithm into an Autodesk World drawing, it follows the
steps in the algorithm and displays the finished image accordingly.
Note: In order to precisely overlay multiple images (as you will do next), the images must
have the same coordinate system information.
Start a new project
1 Start a new project by choosing File > New, then clicking Blank Template.
Set the coordinate system for the new project
1 Choose File > Properties.
2 Click the Coordinate System tab, then click Change....
3 On the Project Detail dialog, select UTM27-11 from the Coordinate
System list.
Set the data viewing coordinate type
1 Choose Tools > Format Options.
2 Click the Units tab, then select m from the ‘User Unit’ list.
3 Click the Coordinate tab, select Projection Coordinate from the ‘Display
Type’ list, then click OK.
The display coordinates are now set to the units of the map projection (meters of
Northings and Eastings in UTM zone 11.)
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Create drawing layers to display three different images
1 Choose File > Data Manager.
The Data Manager dialog lets you add and controls layers in your drawings.
2 Click the Drawing Data tab to view drawing layers
Drawing Data tab
3 Right-click on ‘Drawing1’ then select New Layer.
A new ‘Layer1’ is added in addition to the default ‘0’ layer.
4 Click on the ‘Layer1’ text and change it to satellite image.
5 Right-click on ‘Drawing1’ again, select New Layer, then name the new layer
landuse image.
6 Right-click on ‘Drawing1’ again, select New Layer, then name the new layer
terrain image.
You should have three new labelled layers (the order does not matter for now):
new drawing layers where
images will be inserted
7 Click Close on the Data Manager dialog box.
Insert an ER Mapper satellite image algorithm (.alg) file
1 Choose Insert > ER Mapper Image.
2 On the Insert ER Mapper Image dialog, click the Image tab, then click
Browse.
3 On the Insert Picture dialog, select Algorithms (*.alg) from the ‘Files of
Type’ list.
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Note: When you insert an algorithm file, the Bilinear Smoothing and Contrast Stretching
options are disabled because the algorithm file contains the contrast enhancement
and other information.
4 Double-click on the folder where ER Mapper is installed, then open the
‘examples/Functions_And_Features/Data_Fusion’ folder.
A list of ER Mapper algorithm (.alg) files appears. These algorithms all show
different ways of merging (or “fusing”) two different images into one picture.
5 Double-click on the file ‘Brovey_Transform.alg.’
Tip:
You need a license for ER Mapper to create algorithms, but you can
insert and view them in directly in Autodesk World. This means that anyone using
ER Mapper can create algorithms and send them to you for use in your projects.
6 Click General tab, then select satellite image from the ‘Layer’ list.
select layer where
image will be inserted
You can insert ER Mapper algorithms (.alg) and datasets (.ers), as well as TIFF,
BMP, ARC/INFO-GeoSPOT HDR, and others.
7 Click OK to insert the image into the drawing layer, then click Zoom All
or choose View > Zoom All to display it.
Autodesk World displays a color image of the San Diego, California area. This is a
merge of a Landsat TM satellite image (bands 5, 4 and 2) and a SPOT
Panchromatic satellite image. By merging the two types of data, you get the high
spatial detail provided by the SPOT Pan image (10-meter resolution) with the
multispectral color information provided by the Landsat TM image (seven bands at
30-meter resolution).
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The Brovey Transform is a mathematical way of combining the two images that
also greatly enhances the color. Merging or fusion techniques like this are used to
create to combine the strengths of different satellite sensors and create up-to-date
views of the earth’s surface.
8 Click Zoom Window
(or choose View > Zoom Window), then drag a
box over the central part of the image to zoom into it.
The image shows a high resolution, color-enhanced view of the area. The
ER Mapper algorithm creates this image interactively from the two separate
Landsat and SPOT satellite imagery files. (The Brovey Transform technique
usually requires up to three intermediate image files to be created when using
traditional imaging software, but ER Mapper performs the processing in real time
from the two source images without creating intermediate files.)
9 When finished, click the Zoom All
to zoom out to the full image extents.
button or choose View > Zoom All
Insert a second algorithm image showing thematic landuse
1 Choose Insert > ER Mapper Image.
2 On the Insert ER Mapper Image dialog, click the Image tab, then click
Browse.
3 Double-click on the folder where ER Mapper is installed, then open the
‘examples/Functions_And_Features/Classification_Display’ folder.
A list of ER Mapper algorithm (.alg) files appears. These algorithms all show
different ways of merging (or “fusing”) two different images into one picture.
4 Double-click on the file ‘Isoclass_classification.alg.’
5 Click General tab, then select landuse image from the ‘Layer’ list.
6 Click OK to insert the image into the layer and display it.
Autodesk World displays a thematic color image of the same area of San Diego.
Different colors correspond to different types of landuse in the area. This image
was created from a 1985 Landsat TM satellite image using ER Mapper’s
ISOCLASS unsupervised classification feature. Classification groups pixels with
similar spectral values into classes that can represent different types of landuse or
land cover.
Insert a third algorithm image showing terrain and topography
1 Choose Insert > ER Mapper Image.
2 On the Insert ER Mapper Image dialog, click the Image tab, then click
Browse.
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3 Double-click on the folder where ER Mapper is installed, then open the
‘examples/Data_Types/Digital_Elevation’ folder.
These algorithms all show different ways displaying and processing digital
elevation model (DEM) data files.
4 Double-click on the file ‘Colordrape.alg.’
5 Click General tab, then select terrain image from the ‘Layer’ list.
6 Click OK to insert the image into the layer and display it.
Autodesk World displays a color shaded relief (or “colordrape”) image of the same
area of San Diego. Colors represent elevation (reds are highest) and the shading
effect highlights topographic features such as hills and valleys. This image is
illuminated from the northeast, so shadows appear on the southwest side of terrain
features. ER Mapper has a built-in “realtime shading” feature that lets you
interactively change the shading parameters without creating output files.
View any of the three images
It is often helpful to “stack” multiple different types of images of the same
geographic area (as you did here). Images are treated as CAD entities in Autodesk
World, so you stack multiple images the same way you stack vector data–put each
image on a separate layer and just turn the layers on and off. You can also control
the redraw order (which image is on top) of the layers by dragging them around in
the Display Manager to achieve the desired ordering.
1 Choose View > Display Manager.
2 In the Display Manager dialog, turn off the Entity Style checkboxes for the
‘landuse image’ and the ‘terrain image.’
turn off landuse
and terrain images
3 Press F5 (or select View > Refresh View).
The merged color satellite image displays.
4 In the Display Manager, turn off the ‘satellite image’ checkbox and turn on
the ‘landuse image’ checkbox, then press F5.
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5 View any of the three images by turning on its layer and turning the other
two off, then pressing F5 to refresh the view.
These simple examples show how you can use the power of ER Mapper algorithms
to showing various “views” of your image data as backdrops for analysis of your
vector data in Autodesk World.
Close the project
1 If desired, save your project using File > Save As....
2 Choose File > Close to close the project.
3: Combining image and drawing data
Objectives
Learn to use both image (raster) and drawing (vector) data in a project. In this
example, you will overlay a network of roads on a small aerial photograph image.
Note: Before beginning, make sure the ‘AutoCAD DXF’ GDX driver has been added to
Autodesk World. Consult your Autodesk World documentation or on-line help if
needed to do this before continuing.
Start a new project
1 Start a new project by choosing File > New, then clicking Blank Template.
Set the coordinate system for the new project
1 Choose File > Properties.
2 Click the Coordinate System tab, then click Change....
3 On the Project Detail dialog, select UTM27-11 from the Coordinate
System list.
Set the data viewing coordinate type
1 Choose Tools > Format Options.
2 Click the Units tab, then select m from the ‘User Unit’ list.
3 Click the Coordinate tab, select Projection Coordinate from the ‘Display
Type’ list, then click OK.
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The display coordinates are now set to the units of the map projection (meters of
Northings and Eastings in UTM zone 11.)
Create a drawing layer to display an airphoto image
1 Choose File > Data Manager.
2 Click the Drawing Data tab to view drawing layers.
3 Right-click on ‘Drawing1’ then select New Layer.
4 Click on the ‘Layer1’ text and change it to airphoto image.
Insert an ER Mapper airphoto image into the drawing
1 Choose Insert > ER Mapper Image.
2 On the Insert ER Mapper Image dialog, click the Image tab, then click
Browse.
3 From the ‘Files of Type’ list, select Datasets (*.ers).
4 Double-click on the folder where ER Mapper is installed, then open the
‘examples/Shared_Data’ folder.
5 Double-click on the file ‘Airphoto.ers.’
6 Turn on the ‘Bilinear Smoothing’ and ‘Contrast Stretching’ options.
7 Click General tab, then select airphoto image from the ‘Layer’ list.
8 Click OK to insert the image into the layer and display it.
9 Click the Zoom All
button or choose View > Zoom All.
Autodesk World displays a color aerial photograph of small part of the downtown
San Diego, California area.
Open a DXF drawing to overlay on the airphoto image
1 Choose File > Data Manager.
2 Click the Drawing Data tab, then click the Open Drawing
button.
3 From the ‘Files of Type’ list, select Autodesk DXF File (*.dxf).
Note: If ‘Autodesk DXF’ does not appear as a filetype option, you need to install the
AutoCAD DXF GDX driver.
4 Open the ER Mapper ‘examples/Data_Types_AutoCAD_DXF’ folder.
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5 Double-click on the file ‘Roads.dxf.’
The DXF file is added as a layer in your project.
6 Click Close on the Data Manager, then click the Zoom All
choose View > Zoom All.
button or
Autodesk World displays a vector road network over the airphoto image. This is a
very simple example of combining image and drawing (vector) data. This is the
most common way you will be using the ER Mapper image handling capabilities
within Autodesk World.
Close the Autodesk World application
1 If desired, save your project using File > Save As....
2 Close Autodesk World by clicking the Close
window or selecting File > Exit.
What you
learned...
348
button on the application
After completing these exercises, you know how to perform the following tasks in
Autodesk World:
•
Insert an ER Mapper image into an Autodesk World drawing
•
Enhance the image contrast and apply image smoothing
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Chapter 20 Autodesk World Users ● 3: Combining image and drawing data
•
Choose equivalent coordinate systems in Autodesk World and ER Mapper
•
Insert an ER Mapper smart data algorithm into an Autodesk World drawing
•
Stack and change the order of multiple images in a drawing
•
Combine image and vector drawing data in a project
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A
System setup
This appendix describes the steps needed to install the training datasets so that
students can perform the hands-on exercises in this manual. Most of the hands-on
exercises in this workbook require students to access the airphoto example images
supplied with ER Mapper 6.
Note: Before beginning the installation, you must have at least 450 Mb of free disk space
(310 Mb for the files on the CD-ROM and 140 Mb additional space for files to be
created during the exercises.)
Windows installation of training datasets
1 Create a new directory named “airphoto_training” inside the directory
ERMAPPER/dataset.
This is the directory where the training datasets are assumed to reside.
2 Use the Windows File Manager or Explorer to copy all the files on the CDROM into the “ERMAPPER/dataset/airphoto_training” directory.
The datasets are now accessible to users performing the exercises.
The datasets are now accessible to users performing the exercises.
ER Mapper Workbook - Airphoto Mosaic Applications 351
Appendix A#System setup z Windows installation of training datasets
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B
Reference texts
This appendix provides references to textbooks that describe uses, interpretation
and processing of airphotos. These books will be very helpful to those who want to
learn more about interpretation of airphotos and their applications, and also
contain many references to other sources of data and publications.
Avery, E. A., and G. L. Berlin. 1992. Fundamentals of Remote Sensing and
Airphoto Interpretation, Macmillan Publishing Company, New York, N.Y, USA.
Faulkner, E. 1995. Aerial Mapping: Methods and Applications, CRC Press, Boca
Raton, Fla. USA.
Lillesand, T. M., and R. W. Kiefer. 1991. Remote Sensing and Image
Interpretation, John Wiley and Sons, Inc. New York, N.Y, USA.
ER Mapper Workbook - Airphoto Mosaic Applications 353
Appendix # z
354
ER Mapper Workbook - Airphoto Mosaic Applications
Index
A
airphotos
annotating 227
color balancing 157
composing maps 217
contrast enhancement 59
exporting 245
haze (blue cast) removal 172
importing 54
mosaic creation 20, 141
rectifying (geocoding) 89
saving and exporting 253
scanning 19
scanning and display 74
types 18
viewing overlap areas 181
Algorithm dialog
overview 51
Algorithm Geoposition Extents dialog box
Extents options 204
Geolink options 263
Zoom options 43
algorithm layers. See layers
algorithms
basic concepts 28, 49, 74
changing color table 58
commenting 69
ER Mapper Workbook - Airphoto Applications 355
Index
creating automatically 50
creating manually 50
entering description 69, 87
mosaics 143, 160, 166, 208
opening 38
plotting as map object 241
printing 242
process diagram 52
saving 69, 87, 155, 170, 194, 199, 201, 205, 214
using as templates 51
annotation. See map composition
ArcView GIS 301
ER Mapper imagery extension 301
ArcView GIS ER Mapper plug-in
how to obtain 302
loading 303
opening ER Mapper images 304
overview 301
tutorial 303
using with ER Mapper 302
vector data 310
zoom and pan 306, 315
autoclip transform
concept 65
setting percent clip 203
Autodesk products
save/export from ER Mapper 255
Autodesk World 335
bilinear smoothing 339
contrast enhancement 339
inserting ER Mapper images 337
setting coordinate system 338
tutorial 335
using images and drawing data 346
using multiple images 341
C
camera calibration report 113
Camera file 122
Camera Wizard 117
Camera attributes page 119
Camera identification page 118
Fiducial point offsets page 121
Focal length 119
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ER Mapper Workbook - Airphoto Applications
Index
Number of Fiducial points page 120
X offset to principal point 119
Y offset to principal point 119
clip masks for maps 224
Color (RGB) 247
Color Balancing Wizard for Airphotos 209
Color Mode
relation to layer type 86
color tables 58
comments
defining 69
viewing 71
composing maps. See map composition
compression of imagery 280
Compression Wizard
Actual compression ratio 249
Compress to Grayscale or RGB 247
saving the compressed image 247
Target Compression ratio 248
contrast enhancement 59
automatic 67
manual 62
D
data structure diagram 51
dialog boxes 32
text entry 34
displaying datasets 57
E
Enterprise wide imagery 277
definition 278
free ER Mapper plug-ins 279
problems 277
solutions 279
ER Mapper
compression technology 280
dialog boxes 32
file choosers 33
help system 34
introduction 17, 317
main menu 31
product capabilities 279
ER Mapper Workbook - Airphoto Applications 357
Index
raster datasets 22
toolbars 31
user interface 29
vector datasets 22
ER Mapper plug-ins
for ArcView GIS 301
for MapInfo (MapImagery) 317
for office applications 291
ER Viewer 283
how to obtain 283
measuring distances 287
opening images 285
panning (roaming) images 287
printing images 289
product capabilities 283
tutorial 284
using as OLE server 291
viewing image properties 289
zooming (magnifying) images 286
ESRI ArcView GIS 301
ESRI products
save/export from ER Mapper 255
exporting data 25, 253
resampling cell size 261, 264, 269
to Autodesk products 255
to ESRI .hdr format 264
to MapInfo 255
to TIFF format 266
F
feathering images 180, 192
fiducial points 123
file chooser dialog boxes 33
free imagery plugins for GIS and office applications 245
G
Gaussian equalization 66
setting std. dev. 67
GCP Edit dialog box 130
GCP Setup tab 126
Geocode Output Extents dialog 132
geocoding
advanced orthorectification 113
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ER Mapper Workbook - Airphoto Applications
Index
camera calibration report 113
Compute FROM function 101
GCP display options 103
picking first 4 GCPs 97
picking points from overview 101
RMS errors 100
Geocoding Wizard 113
Auto zoom 129
Auto Zoom option 103
Calculate from point button 101
Cell Attributes box 107
Exterior Orientation Setup tab 135
Fiducial Point Edit tab 122, 135
GCP Edit tab 98, 103, 127
GCP Setup tab 126
Ortho Setup tab 116, 135
Orthorectify using exterior orientation 116, 134
Output Coordinate Space dialog 127
Rectify tab 106, 131, 137
resampling 107
Use a DEM file as height 117
Zoom to current GCP button 103
geocoding. See rectification
GID Australia 317
GIS systems
exporting images to 245
raster image formats 255
resampling cell size for 254
subsetting images for 254
using images in 253
graphics formats
exporting to 25
using in map composition 241
ground control points
adjusting 103
labelling 105
locking 105
overview 90
picking 98
saving to dataset 106
viewing error bars 103
H
hardcopy printing 25
ER Mapper Workbook - Airphoto Applications 359
Index
haze corrections 172
help system 34
histogram equalization 66
I
Image Display and Mosaic Wizard 76, 160
Image Display and Mosaicing Wizard 149
image files. See raster datasets
image processing
concepts 25
enhancements 23
ER Mapper algorithms 27
traditional techniques 27
image rectification parameters 127
image windows
closing 46
loading datasets 57
measuring distances 111
moving 39
moving to front 45
opening 38
panning with buttons 42
resizing 40
selecting current 46
shaping to fit image 152
using multiple windows 44
viewing coordinates 110
zooming with buttons 42
zooming with mouse 41
imagery
compression 281
file formats 277
file sizes 277, 281
served over the internet 278, 279
sharing among applications 277
sharing via OLE 291
using in office applications 291
importing airphoto images 55
L
Layer tab 52
layers 52
adding 83
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Index
Annotation/Map Composition 217
changing type 84
deleting 83
dragging and dropping 147
duplicating 84
labelling 68
loading data into 82
moving between 85, 203, 204
moving up or down 81
selecting 79
selecting bands 84
setting display priority 147
shortcut menu 84, 147
with Color Mode 86
Line Style dialog box 228
loading datasets 57
OK vs Apply button 82
M
magnifying images. See zooming
map composition
adding inset images 241
area of polygon 229
basic concepts 217
clip masks 224
deleting objects 230
drag and drop objects 237
drawing annotation 228
drawing map objects 234
duplicating (cloning) objects 231
Fast Preview option 238
importing graphics formats 241
importing text 241
length of line 228
object attributes 241
object selection tools 230
page background color 223
Page Relative option 241
Page Setup options 242
polygon attributes 229
polyline attributes 228
resizing/positioning objects 239
saving to disk 239
selecting multiple objects 231
ER Mapper Workbook - Airphoto Applications 361
Index
selecting objects 228
setting map object attributes 225, 236
special features 241
text attributes 231, 232
map projections. See rectification 113
MapImagery plug-in 317
algorithm (.alg) files created by 330
commercial version 318
contrast enhancement 332
controlling image layers 326
free version 317
how to obtain 318
measuring distances 321
opening ER Mapper algorithms 322
opening ER Mapper images 320
overlaying vector data 327
setting image map projection 321, 331
table (.tab) files created by 330
tutorial 318
using with ER Mapper 318
viewing image coordinates 322
zoom and pan 321
MapInfo 317
export from ER Mapper 255
link with ER Mapper 255
MapImagery plug-in 317
measuring distances 111
mensuration 111
Microsoft Office applications 291
mosaicing 20
analyze images 209
basic steps 21
capabilities 142
creating algorithms 143, 208
display band 151
display method 151
feathering 210
file types 150
mosaic properties 150
requirements 141
RGB 123 154
setting display priority 142, 147
turning images on/off 147, 153
zooming to all datasets 146
mosaicking
creating algorithms 160, 166
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Index
viewing overlap areas 181
zooming to all datasets 164
mouse buttons 30
mouse pointer
Hand mode 41
Pointer mode 110
shapes 30
Zoom mode 40
ZoomBox mode 41
O
Object Linking and Embedding (OLE) 291
office applications
using imagery in 291
OLE
displaying images 294
drag and drop images 295
overview 292
tutorial 291
orthorectification
Attitude kappa 114, 136
Attitude omega 113, 136
Attitude phi 114, 136
Camera Wizard 117
Exposure center X Y Z 136
exterior orientation 114, 116, 135, 136
fiducial points 124
Focal length 119
Scale 137
X offset to principal point 119
Y offset to principal point 119
P
Page Setup dialog box 220
panning images
with buttons 43
with mouse 41
polygon attributes 229
area measurement 229
color and shading 229
polyline attributes 228, 229
polylines
color and style attributes 228
ER Mapper Workbook - Airphoto Applications 363
Index
editing points 228
length (geographic units) 228
smoothing (spline) 228
Postscript files
printing to 25
using in map composition 217
printing images 25, 242
process stream diagram 52
Pseudocolor color mode 58
R
Raster Dataset dialog 82
Apply button 82
OK vs Apply buttons 82
raster datasets
description 26
importing 22
mosaicing 177, 195, 207
mosaics 141
opening directly 75
raster images
mosaicing 207
rectification 23
adjusting GCPs 103
Compute FROM function 101
GCP display options 103, 130
picking first 4 GCPs 97
picking points from overview 101
RMS errors 100
Red Green Blue (RGB) color mode 73
Refresh Image button 39
regions 177
defining 183
hidden stitch lines 178
naming 185, 187
referencing in formulas 189
RMS errors 100
S
saving data 253
cropping/subsetting 254
for Autodesk products 255
for MapInfo 255
364
ER Mapper Workbook - Airphoto Applications
Index
in UDF format 257
resampling cell size 261, 264, 269
to ESRI .hdr format 264
to TIFF format 266
shortcut menus
layers 147
surfaces 181
surfaces 52
changing color mode 181
expanding/contracting 80
shortcut menu 181
T
tab pages 52
text attributes 231
Text Style dialog box 231
toolbars
displaying 37
hiding 37
overview 31
using 37
Transform dialog box 60
transforms
autoclipping 65, 203
Gaussian equalization 66
histogram equalization 66
viewing 60
viewing for other layers 85, 203, 204
U
UDF images 257
V
View Mode 52
vignetting 158
W
warping images. See rectification 113
wavelet compression technology 245
ER Mapper Workbook - Airphoto Applications 365
Index
wavelet image compression 280
windows. See image windows
word processing
inserting images via OLE 291
Z
zooming images
out to full extents 42, 44
to current dataset extents 148
to page extents or contents 227
to specific dataset extents 153
with buttons 43
with mouse 41
366
ER Mapper Workbook - Airphoto Applications
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