ER Mapper

ER Mapper
ER Mapper
Airphoto Tutorial
September 2008
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Table of Contents
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
About this manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Setting up practice datasets . . . . . . . . . . . . . . . . . . . . 1
Typographical conventions . . . . . . . . . . . . . . . . . . . . . 1
Airphoto mosaics and ER Mapper . . . . . . . . . . . . . . . . . . . . . 3
Overview of airphotos and applications . . . . . . . . . . . . 3
Types of airphotos . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Digitizing (scanning) of airphotos . . . . . . . . . . . . . . . . 4
Digital Orthophoto Quadrangles . . . . . . . . . . . . . . . . . 6
Creating airphoto mosaics . . . . . . . . . . .
Data load/import . . . . . . . . . . . . . . . . . . .
Image display . . . . . . . . . . . . . . . . . . . . .
Image geocoding . . . . . . . . . . . . . . . . . . .
Creating image mosaics . . . . . . . . . . . . . . .
Image enhancement and correction . . . . . .
Data saving and compression . . . . . . . . . . .
Map composition . . . . . . . . . . . . . . . . . . . .
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Image processing concepts . . . . . . . . . . . . . . . . . . . . 11
ER Mapper image processing . . . . . . . . . . . . . . . . . . . 12
Opening and viewing an image . . . . . . . . . . . . . . . . . . . . . 13
About the algorithms concept . . . . . . . . . . . . . . . . . . 13
What is an algorithm data view? . . . . . . . . . . . . . . . . . . . . 13
The Process Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1: Displaying an airphoto image . . . . . . . . . . . . . .
About loading data . . . . . . . . . . . . . . . . . . . . . . . . . . .
Open an image window and the Algorithm dialog . . . . . .
Load the airphoto dataset into the Pseudo Layer . . . . . .
Load the airphoto dataset into the Algorithm . . . . . . . . .
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2: Selecting layers and adjusting contrast . . . . . . .
Select the Layer tab in the Algorithm dialog . . . . . . . . . .
Display the histogram for the Red layer . . . . . . . . . . . . .
Apply a 99% clip transform to the data . . . . . . . . . . . . .
Apply a Histogram equalize transform to the data . . . . .
Use 99% Contrast Enhancement button . . . . . . . . . . . .
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3: Labeling and saving the algorithm . . . . . . . . . . .
Enter a description for the entire algorithm . . . . . . . . . .
Save the processing steps to an algorithm file on disk . . .
Add comments to the algorithm . . . . . . . . . . . . . . . . . .
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4: Reloading and viewing the algorithm . . . . . . . . . . . 26
Table of Contents
iii
Open a second image window . . . . . . . . . .
Open the RGB algorithm you created earlier
View the algorithm comments . . . . . . . . . .
Close both image windows and the Algorithm
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Using GeoTIFF/TFW images . . . . . . . . . . . . . . . . . . . . . . . 29
Georeferencing information . . . . . . . . . . . . . . . . . . . . 29
About GeoTIFF/TFW . . . . . . . . . . . . . . . . . . . . . . . . . 29
GeoTIFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
TFW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
GeoTIFF/TFW and foot-based projections . . . . . . . . . 30
\GeoTIFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
TFW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . . 31
1: Edit the TIFF image header . . . . . . . . . . . . . . . .
Examine the current header information . . . . . . . . . . . .
Open the Change Datum/Projection/Cell size wizard . . . .
Open the TIFF image . . . . . . . . . . . . . . . . . . . . . . . . . .
View the TIFF image georeferencing information . . . . . .
Save the TIFF image as GeoTIFF . . . . . . . . . . . . . . . . .
Display the GeoTIFF image . . . . . . . . . . . . . . . . . . . . .
View the GeoTIFF georeferencing information . . . . . . . .
Close all windows . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Image orthorectification . . . . . . . . . . . . . . . . . . . . . . . . . 41
About image rectification . . . . . . . . . . . . . . . . . . . . . 41
Ground Control Points . . . . . . . . . . . . . . . . . . . . . . . . 42
About orthorectification . . . .
DEM file . . . . . . . . . . . . . . . . .
Camera file . . . . . . . . . . . . . .
About fiducial points . . . . . . . .
Advanced orthorectification . . .
Input data requirements . . . . .
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Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . . 47
1: Orthorectify an airphoto using GCPs . . . . . . . . . . . 48
Open the Geocoding Wizard . . . . . . . . . . . . . . . . . . . . . . . 48
Enter terrain and camera details . . . . . . . . . . . . . . . . . . . . 49
Create a Camera file . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Edit the fiducial points . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Setup Ground Control Points . . . . . . . . . . . . . . . . . . . . . . 60
Edit Ground Control Points . . . . . . . . . . . . . . . . . . . . . . . . 61
Pick a second GCP in the lower-left of the reference image . 63
Try some other features on the Geocoding Wizard GCP Edit dialog
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Rectify the image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Evaluate the image orthorectification . . . . . . . . . . . . . . . . 67
Display the two images to evaluate registration . . . . . . . . . 68
Close all windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
2: Orthorectify an airphoto using Exterior Orientation . .
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Table of Contents
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Open the Geocoding Wizard . . . . . . . . . . . . . .
Enter Exterior Orientation parameters . . . . . . .
Rectify the image . . . . . . . . . . . . . . . . . . . . .
Evaluate the image orthorectification . . . . . . .
Display the two images to evaluate registration
Close all windows . . . . . . . . . . . . . . . . . . . . .
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Reprojecting images . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
UTM and State Plane projections . . . . . . . . . . . . . . . . 75
UTM projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
State plane projections . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . . 76
1: Import an image into ER Mapper . . . . . . . . . . . . . . 76
Importing a TIFF image . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Open the TIFF import dialog . . . . . . . . . . . . . . . . . . . . . . . 77
2: Reproject the image . . . .
Open the Geocoding WIzard . .
Map to Map setup . . . . . . . . .
Rectify the image . . . . . . . . .
Close all windows . . . . . . . . .
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Assembling image mosaics . . . . . . . . . . . . . . . . . . . . . . . . 85
About assembling mosaics . . . . . . . . . . . . . . . . . . . . 85
Requirements for mosaics . . . . . . . . . . . . . . . . . . . . . . . . 85
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . . 86
1: Creating mosaics automatically . . . . . . . . . . . . .
Start the Image Display and Mosaic wizard . . . . . . . . . .
Select file types to mosaic . . . . . . . . . . . . . . . . . . . . . .
Select mosaic properties . . . . . . . . . . . . . . . . . . . . . . .
Select display method . . . . . . . . . . . . . . . . . . . . . . . . .
Select display band . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mosaic and display the images . . . . . . . . . . . . . . . . . . .
Turn the top image on and off . . . . . . . . . . . . . . . . . . .
Zoom in to the geographic extents of any image dataset .
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2: Creating an RGB image mosaic . . . . . . . . . . . . . . . 91
Change the image display method . . . . . . . . . . . . . . . . . . 91
3: Adding a GeoTIFF image to the mosaic
Add an extra image to the mosaic . . . . . . . .
Save the mosaic algorithm to disk . . . . . . . .
Close all image windows and dialog boxes . . .
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Color balancing image mosaics . . . . . . . . . . . . . . . . . . . . . 97
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . . 97
1: Color balancing the mosaic . . . . . . . . . . . . . . . . . . 97
Open the airphoto mosaic . . . . . . . . . . . . . . . . . . . . . . . . 97
Close the image window and Algorithm dialog . . . . . . . . . 105
Table of Contents
v
Compressing images . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
About Enhanced Compression Wavelet (ECW) compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . 107
1: Saving a compressed image to disk . .
Input image to be compressed . . . . . . . . . .
Compressed image file name . . . . . . . . . . .
Compress to Grayscale, RGB or Multi . . . . .
Select Compression ratio . . . . . . . . . . . . . .
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Exporting to GIS systems . . . . . . . . . . . . . . . . . . . . . . . 115
About use in GIS systems . . .
Cropping or subsetting images .
Spatial resolution (cell size) . . .
Raster formats for GIS and DMS
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Using compressed images in GIS applications . . . . . 117
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . 117
1: Defining an area of interest . . . . . . . . . . . . . . . . . 117
Open the final mosaic algorithm . . . . . . . . . . . . . . . . . . . 117
Zoom into the project area . . . . . . . . . . . . . . . . . . . . . . 118
2: Creating a UDF dataset . . . . . . . . . . . . . . . . . . . . 119
Setup the algorithm for dataset output . . . . . . . . . . . . . . 119
Save the project area to a full resolution UDF dataset . . . . 120
Display the new dataset in RGB . . . . . . . . . . . . . . . . . . . 121
View information about the new dataset . . . . . . . . . . . . . 121
Save the project area to a half resolution UDF dataset . . . 122
Display the half resolution dataset in RGB . . . . . . . . . . . . 123
View information about the half resolution dataset . . . . . . 124
Geolink the subset images to see the resolution difference 124
3: Creating a “.hdr” file for ESRI products . . . . . . .
Close the half resolution subset image window . . . . . . . .
Zoom out on the full resolution subset image . . . . . . . . .
Create the “.hdr” file for the ER Mapper dataset . . . . . . .
Close the subset image window . . . . . . . . . . . . . . . . . .
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4: Saving a subset image to a TIFF file . . . . . . . . . . 128
Zoom into the project area . . . . . . . . . . . . . . . . . . . . . . 128
Save the project area to a true color (24-bit) TIFF file . . . . 128
Display the new dataset in RGB . . . . . . . . . . . . . . . . . . . 129
View information about the new dataset . . . . . . . . . . . . . 130
Save the project area to a half resolution ER Mapper dataset . .
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Display the half resolution dataset in RGB . . . . . . . . . . . . 131
View information about the half resolution dataset . . . . . . 132
Close the image windows and the Algorithm dialog . . . . . . 132
Windows® applications (OLE)
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About ER Viewer . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
What is OLE? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
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Table of Contents
Sharing image files using OLE . . . . . . . . . . . . . . . . . . . . 134
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . 135
1: Using OLE to display images . . . . . . . . . . . . . . . . 135
Start Microsoft Word (or other OLE-enabled word processor) . .
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Open the Windows® Explorer . . . . . . . . . . . . . . . . . . . . 136
Drag an algorithm image file into the Word document . . . . 136
Zoom and roam using the ER Viewer toolbar . . . . . . . . . . 136
Return to the Word application . . . . . . . . . . . . . . . . . . . . 137
Insert the ECW compressed image into the document . . . . 137
Zoom into and center the compressed image . . . . . . . . . . 137
Copy and paste the compressed image . . . . . . . . . . . . . . 137
(Optional) Save your word processing document. . . . . . . . 138
Image Web Servers . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
ER Mapper Image Web Server . . . . . . . . . . . . . . . . . 139
Server side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Client side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Hands-on exercises . . . . . . . . . . . . . . . . . . . . . . . . . 142
1: Open an image in ER Mapper . . . . . . .
Load the image into an algorithm . . . . . . . .
Saving the image as an algorithm . . . . . . . .
Reloading the algorithm . . . . . . . . . . . . . .
Using the History file . . . . . . . . . . . . . . . . .
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2: Open an image in ArcView ® GIS . . . . .
Open a URL file . . . . . . . . . . . . . . . . . . . .
Zoom, pan and measure the image . . . . . . .
Close ArcView® GIS . . . . . . . . . . . . . . . . .
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Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Table of Contents
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viii
Table of Contents
About this manual
This manual is intended to get you started with using ER Mapper to
create mosaics of digital aerial photographs. It provides simple stepby-step procedures that give you hands-on practice using advanced
features of the software.
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
accessible directly from the on-line help system.)
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
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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.
Setting up
practice datasets
The exercises in this manual assume that ER Mapper is installed and
licensed, and that the example airphoto datasets have been installed
in the “examples\functions_and_features\airphoto_tutorial”
directory.
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
About this manual
button.”
1
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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.”
2
About this manual
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 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:
Types of airphotos
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land use/land cover mapping
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urban and regional planning
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environmental assessment
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civil engineering
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geologic and soil mapping
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agricultural and forestry applications
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water resource and wetland applications
There are generally four types of airphotos in common use, and
these are created by using specific types of film in the camera:
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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 grayscale on a computer.
Airphoto mosaics and ER Mapper
3
Digitizing
(scanning) of
airphotos
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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.
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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 (0.71.0) 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 grayscale.
•
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 (0.7-1.0)
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.
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 to convert
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.
Aerial photographs normally have fiducial marks around the
edges. The positions of these marks are crucial for
orthorectification. It is, therefore, essential that the scanner
used is large enough to include the fiducial marks in the scanned
image.
Two factors affect the resolution, or size of features that can be
detected, in the digital image of the aerial photograph. These factors
are:
•
4
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.
Airphoto mosaics and ER Mapper
•
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.
Photo scale:
10000
24000
40000
Km. across:
2.3
5.5
9.1
Scanned image file sizes
# of
pixels
Pixel size in meters
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
21Mb
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 or via an Image Web
Server, in a format supported by ER Mapper. This will save you
having to scan the photos yourself.
Image formats supported by ER Mapper include:
•
ER Mapper Algorithm (.alg)
•
ER Mapper Raster Dataset (.ers)
•
ER Mapper Compressed Image (.ecw)
•
Windows® Bitmap (.bmp)
•
ESRI BIL and GeoSPOT (.hdr)
•
GeoTIFF/TIFF (.tif)
•
1 bit tiled tiff
•
1bit strip tiff (compressed and uncompressed)
•
1bit scanline tiff (compressed and uncompressed)
•
8 bit grayscale tiled tiff
•
8 bit RGB contiguous tiled tiff
Airphoto mosaics and ER Mapper
5
Digital
Orthophoto
Quadrangles
•
8 bit RGB separate tiled tiff
•
JPEG (.jpg)
•
USGS DOQQ (Grayscale)
•
RESTEC/NASDA CEOS (.dat)
Airphoto images can be supplied as Digital Orthophoto Quarter
Quadrangles, known as DOQQs.
A digital orthophoto is a digital image of an aerial photograph in
which displacements caused by the camera and the terrain have
already been removed. Therefore it combines the image
characteristics of a photograph with the geometric qualities of a
map. A DOQ image typically covers one-quarter of a 1:24,000 scale
USGS topographic map plus a little overlap. The resolution of the
image is quite high at one square meter per pixel. As a result of this
fine cell size, these images consume large quantities of disk space.
A DOQQ is a subset of a DOQ, in that it refers to a Digital Orthophoto
Quarter Quad. There are four DOQQs in a DOQ.
You can open DOQQ images directly in ER Mapper, and then use
ER Mapper wizards to mosaic and balance them.
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.
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.
6
Airphoto mosaics and ER Mapper
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.
Read/Import
digital
airphotos
Read digital airphoto image files stored on tape,
CD-ROM, etc. into ER Mapper. If necessary,
convert to ER Mapper image format
(using ER Mapper import utilities)
Initial
image display
& evaluation
View image data to evaluate
quality or area of 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.
Create
mosaic
of images
Balance
mosaic
of images
Assemble rectified, enhanced images into a mosaic.
Balance contrast across the mosaic, and minimize
visible seam lines between adjacent images.
Data saving
and/or
compression
Save the processed mosaic in a format suitable for use
in GIS and DMS applications, or for serving from an
Image Web Server.
Annotation
& map
composition
Setup map size/scale, and annotate mosaic of images
with text, lines, shaded polygons, legends, scale
bars, coordinate grids and other map objects.
Airphoto mosaics and ER Mapper
7
Data load/import
The first step in creating an airphoto mosaic is loading or importing
the data you want to use into ER Mapper. Typically the data might
be stored on magnetic tape, CD-ROM, or be available for download
from an Image Web Server over a network.
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 a “.ers” file extension
You can open image files in many different formats in ER Mapper
without having to import them as ER Mapper raster datasets. Some
of these formats contain embedded georeferencing information that
ER Mapper uses to mosaic the images. These formats include ECW
V2 compressed, GeoTIFF and USGS DOQQ. Some TIFF images have
an accompanying ‘World’ file, TIFW, that contains the georeferencing
information. ER Mapper creates a separate .ers header file for these
to accommodate statistical information used for balancing.
Image display
After loading or importing the image data, the next step is usually to
display the image 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:
•
black and white, or grayscale 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)
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 twodimensional 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
8
Raster image data is often 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.
Airphoto mosaics and ER Mapper
•
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, fiducial marks on the image and terrain
details.
If your application requires that your images be registered to one
another or rectified to a map projection, you can use ER Mapper’s
Geocoding Wizard to do this.
DOQQ images have already been orthorectified, so you do not
need to use ER Mapper to do it again.
The Geocoding Wizard only supports the ER Mapper Raster
Dataset format. Images in any other format that require
geocoding will have to be saved as ER Mapper Raster Datasets
first. This includes ECW compressed images.
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 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
mosaics images in a specified directory path.
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.
Airphoto mosaics and ER Mapper
9
Typical image enhancement operations include:
Data saving and
compression
•
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.
•
Color balancing–Use the ER Mapper Color Balancing Wizard to
balance mosaiced images to produce a seamless single image.
Once you have completed processing your data, ER Mapper lets you
save your image in a format suitable for serving, for use or further
processing.
•
ECW Compression enables you to save your imagery in
compressed format for use in other applications or serving from
an Image Web Server.
•
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
those in ECW compressed format, from within many GIS
products.
•
Hardcopy printing is often the final goal of processing and
annotating images, and ER Mapper provides 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.
Map composition
10
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.
Airphoto mosaics and ER Mapper
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 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).
For digitized airphotos, the DNs represent the intensity of reflected
light in the visible, infrared, or other wavelengths of the electromagnetic 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.
Airphoto mosaics and ER Mapper
11
ER Mapper image
processing
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.
With ER Mapper, you need to 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.
In ER Mapper, algorithms can be used for simple viewing of data
such as grayscale or RGB band combinations. Algorithms are also
used for complex processing and modeling 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.
12
Airphoto mosaics and ER Mapper
Opening and viewing an image
This chapter shows you how to open a digitized airphoto in TIFF
format, and how to display it as a color 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.
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:
Opening and viewing an image
•
Names of image 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
13
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 an image dataset directly (Open) and have ER Mapper
automatically display the image 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 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 labeled 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/surface
surface
list of layers
in surface
process diagra
for selected
layer
data
structure
diagram
panel
14
Opening and viewing an image
The Process Diagram
•
Data structure diagram: Shows a list of surfaces and layers
•
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
•
Process diagram: Used to control the processing operations
applied to image(s) in the currently selected layer (displayed
when Layer tab is selected).
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.
display and processing techniques, such as Layer for options for
the current layer, or Surface for options that apply to an entire
surface.
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.
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.
Button
Function
Load Dataset
Use to load an image dataset from disk, or edit or view
information or comments about an image.
Band Selection
Use to select one or more bands in the dataset for use in
generating an image (a drop-down list).
Formula
Use to enter, load, or save a formula to perform image algebra
and other arithmetic operations.
Opening and viewing an image
15
Button
Function
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.
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
What you will
learn...
Before you
begin...
These exercises show you how to open a digitized airphoto in
ER Mapper, display, enhance the image, and then save and reload a
simple image processing algorithm.
After completing these exercises, you will know how to perform the following tasks in
ER Mapper:
•
Load and display an image dataset
•
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.
1: Displaying an
airphoto image
Objectives
16
Learn to open an image window and the Algorithm dialog, load an image, and display
the image in color.
Opening and viewing an image
The sample airphoto tutorial datasets must be installed on your
computer before you can complete this exercise.
About loading data
You can open any of the following image data formats directly into
ER Mapper 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)
In this example you will open an image in TIFF format.
Open an image window
and the Algorithm dialog
1. From the View menu, select Algorithm....
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 (labeled “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.
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.
Opening and viewing an image
17
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 Input File dialog), select the
path ending with \examples.
3. Double-click on the directory named ‘functions_and_features’ and
then ‘airphoto_tutorial’ to open it.
4. Double-click on the image file named ‘1_3_rect.tif’ to load it.
ER Mapper will display only the red band of the color airphoto in a
pseudocolor layer.
18
Opening and viewing an image
5. View the red, green and blue bands individually by selecting them
from the band drop-down list.
select band
Load the airphoto dataset
into the Algorithm
Generally it is more useful to display the Red, Green and Blue bands
of color airphotos together, and not singly.
1. Close the image window, but leave the Algorithm dialog open.
The layer list and process diagram in the Algorithm dialog will now
be blank.
2. On the ER Mapper Standard toolbar, click the Open
button.
The Open file chooser dialog box appears.
3. From the Directories menu (on the Input dialog), select the path
ending with \examples.
4. Double-click on the directory named ‘functions_and_features’ and
then ‘airphoto_tutorial’ to open it.
5. Double-click on the image file named ‘1_3_rect.tif’ to load it.
ER Mapper will now load the Red, Green and Blue bands of the
airphoto into Red, Green and Blue layers, and display the image in
color.
If you open an image by clicking on the Open
or selecting
Open... from the File menu, ER Mapper will automatically display
the image according to the number of bands in the image. In this
instance, the image has three bands, so ER Mapper displays the
image as RGB.
It is often preferable to use the Image Display and Mosaic
Opening and viewing an image
19
Wizard
to open and display an image because it gives you
more control over how the image is displayed. This is described
in “Assembling image mosaics” on page 85.
2: Selecting layers
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.
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.
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 layer
1. In the Algorithm dialog, click on the right-hand Edit Transform
Limits
20
button (blue) in the Red layer process diagram.
Opening and viewing an image
Edit Transform Limits button
2. The Transform dialog box opens showing a histogram of the data
values in the current layer (Red in this case), and options for
modifying the image contrast.
transform line
color bar showing
colors in current
Color Table
(grayscale)
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. Peaks in the histogram show
where there are many pixels with similar data values, and
sometimes indicate identifiable features in an image.
Opening and viewing an image
21
The transform line maps the image data values on the X-axis to the
output display values on the Y-axis. A linear transform line, as shown
above, creates the same input and output histograms. A non-linear
transform line causes the output histogram to be different to the
input 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.
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 selected layer (and
automatically positions the transform line for you. Autoclipping is the
most commonly used contrast enhancement technique for image
datasets.
Autoclipping is not always desirable for airphotos (as opposed to
satellite images) because airphotos often contain data in the
areas that are clipped. This particular image is a good example
of where there is a significant amount of data in the lower
values.
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.
22
Opening and viewing an image
Apply a Histogram
equalize transform to the
data
1. On the Transform dialog, click the Histogram equalize
button.
Histogram equalize button
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 for the selected layer 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 an
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.
The transforms must be set for each layer individually. Use the
Transform dialog R, G and B buttons to select the required
layer.
Use 99% Contrast
Enhancement button
Now you will learn to use a faster, easier way to adjust the image
contrast.
1. On the main ER Mapper menu, click the 99% Contrast
Enhancement
Opening and viewing an image
button.
23
99% Contrast Enhancement
button
ER Mapper runs the algorithm again to display the airphoto, and
automatically adjusts the contrast for all the layers for you. This
button performs the following sequence or actions for you
automatically:
Process->Limits to Actual->Process->99% autoclip->Process
Again, the 99% Contrast Enhancement is not always desirable
for airphotos because it could remove important data from the
image. It is included in this tutorial for descriptive purposes only.
The Refresh
STOP
, 99% Contrast Enhancement
and
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.
3: Labeling 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 entire algorithm
1. In the Algorithm dialog, select the text in the Description text field
(it currently reads ‘Algorithm Not Yet Saved’).
24
Opening and viewing an image
(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 As... file chooser dialog opens.
2. In the Files of Type: field, select ‘ER Mapper Algorithm (.alg)’
3. 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.)
4. Double-click on the directory named ‘Miscellaneous’ and then
‘Tutorial’ to open it.
5. In the Save As: text field, click to place the cursor, then type the
following name for the algorithm file:
Airphoto_RGB
6. Click the Apply button to save the algorithm and OK to close the
dialog.
Your algorithm is now saved to an algorithm file on disk.
Add comments to the
algorithm
1. From the File menu (on the main menu) select Open...
2. From the Directories menu, select the path ending with the text
\examples.
3. Double-click on the directory named ‘Miscellaneous’ and ‘Tutorial’,
and then click on ‘Airphoto_RGB.alg’ to select it. Click on the
Comments button in the Open dialog.
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.
4. In the comments dialog, type the following information to describe
your algorithm:
This algorithm displays the red, green and blue bands
of an airphoto as a grayscale algorithm. A 99% autoclip
transform is used
to increase image contrast.
Opening and viewing an image
25
5. Click OK on the comments dialog to save your comments.
6. Click OK on the Open dialog to close it.
4: 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 RGB 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 ‘Miscellaneous\Tutorial’ directory to open it.
5. Your ‘Airphoto_RGB’ algorithm name should appear in the list.
6. Click once on your algorithm name to highlight it (do not double-
click).
7. 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.
View the algorithm
comments
1. On the Open dialog, click the Comments... button.
26
Opening and viewing an image
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 both 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:
Opening and viewing an image
•
Load and display an image dataset as an RGB 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
27
28
Opening and viewing an image
Using GeoTIFF/TFW images
This chapter explains how you can open and use GeoTIFF images and
TIFF images with TFW files in ER Mapper
Georeferencing
information
You can only mosaic images if they contain georeferencing
information; i.e. that which defines where the image is
geographically located. The ER Mapper Raster Dataset format has a
header file (.ers), separate from the data file which contains the
necessary georeferencing information. The ECW compressed format
has the georeferencing information embedded in the data file as do
GeoTIFF and DOQQ image formats. Other formats can have
associated ‘World’ or ‘Header (.hdr)’ files, similar to .ers header
files, that contain the georeferencing information.
ER Mapper can create .ers header files to hold georeferencing and
statistical information for image files in all supported formats.
ER Mapper uses the information in a .ers header file in preference to
that embedded in the image data file or contained in an associated
‘World’ file.
About
GeoTIFF/TFW
There are two ways of including georeferencing information with
raster images in the TIFF format (Tagged Image File Format) The
first way is to use an accompanying text file, called a ‘World’ File. The
second way is to incorporate the information directly into specially
identified tags in the TIFF file. In this case, the TIFF file is known as
a GeoTiff.
GeoTIFF
GeoTIFF is an industry-wide standard which has been developed by
several organizations in the GIS community for specifying
cartographic information in TIFF tags. Geographic information is
embedded in the TIFF data file in the form of descriptive tags.
TFW
The TFW file is a text file which contains georeferencing information
for an associated raw TIFF file. Known as a World file, it contains the
following information:
Using GeoTIFF/TFW images
•
x resolution
•
amount of translation
•
amount of rotation
•
negative of the y resolution
•
x ground coordinate of pixel 1,1 (upper left)
•
y ground coordinate of pixel 1,1 (upper left)
29
World files are not restricted to TIFF images, and are generally
named the same as the associated image file with a "W" appended.
For example, if the image file is named ‘image1.TIF’, the
corresponding world file is named ‘image1.TFW’.
GeoTIFF/TFW and
foot-based
projections
Below lists and describes the different GeoTiff and TFW foot-based
reprojections.
\GeoTIFF
GeoTIFF images do not have a standard unit (i.e feet or meters) for
the cell sizes. Generally the units are the same as those for the
projection (i.e. cell size is specified in feet for foot-based projections,
and meters for meter based projections). ER Mapper always
interprets the cell size to be in meters, even for foot-based
projections. This could cause problems when you open a GeoTIFF
image (e.g. created with MapInfo® or ArcView® GIS™) with a footbased projection in ER Mapper for processing, and then save it for
use in the original or another application. ER Mapper solves this
potential problem by calculating the correct cell sizes in meters when
opening a GeoTIFF image with a foot-based projection. It then
converts the cell sizes back to feet if you save the image in GeoTIFF
or ECW compressed format.
TFW
World files have the additional problem of not having datum or
projection information. Not knowing the projection, ER Mapper is not
able to determine whether to convert the cell sizes to meters, as it
can with GeoTIFF images.
For this reason, ER Mapper 6.1 introduced the Change
Projection/Datum/Cell Size wizard with which you can edit the
.ers ER Mapper header file associated with the image. It creates a
new .ers header file if one does not already exist. ER Mapper then
uses this information in the .ers header file instead of that in the
TFW World file.
With this wizard you can specify the following information:
•
datum and projection.
•
accept the existing cell size or you can enter a new cell size.
•
recalculate the cell sizes to be the correct value in meters.
Be careful that you enter the correct information. The wizard
only edits the header file, but does not reproject the image.
30
Using GeoTIFF/TFW images
Hands-on
exercises
What you will
learn...
Before you
begin...
These exercises give you practice using ER Mapper’s Change
Projection/Datum/Cell Size Wizard to edit TFW file information
After completing these exercises, you will know how to perform the following tasks in
ER Mapper:
•
Open a TIFF image in ER Mapper
•
Use the Change Projection/Datum/Cell Size Wizard to edit the
header information
•
Save the TIFF file in GeoTIFF format.
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: Edit the TIFF
image header
Objectives
Learn how to use ER Mapper’s Change Datum/Projection/Cell Size Wizard to create a
.ers header file for a TIFF image.
Examine the current
header information
1. Using Windows® Explorer (or similar) temporarily rename the
‘1_3_rect.tfw’ file in the
‘\examples\Functions_And_Features\Airphoto_Tutorial’
directory.
This is the ‘World’ file associated with the ‘1_3_rect.tif’ image file.
Renaming it effectively disassociates it from the image file.
2. On the ER Mapper Common Functions toolbar, click on the Load
Dataset
button.
3. On the Raster Dataset dialog, select ‘GeoTIFF/TIFF(.tif)’ in the
Files of Type field.
4. From the Directories menu (on the Select File dialog), select the
\examples path.
5. Double_click on the ‘Functions_and_Features’ directory to open
it.
6. Double_click on the ‘airphoto_tutorial’ directory.
7. Click on the image dataset ‘1_3_rect.tif’ to select it. Do not load it.
Leave the Raster Dataset dialog box open.
Using GeoTIFF/TFW images
31
8. Click on the Info button to display the Dataset Information dialog
box.
Notice that the Geodetic Datum and Map Projection fields are both
‘RAW’. This indicates that the image does not have any
georeferencing information.
9. Click on the Dataset Information dialog Close button.
10. Using Windows® Explorer (or similar), restore the ‘1_3_rect.tfw’
file to its correct name. This will re-associate it with the ‘1_3_rect.tif’
image file.
11. Click on the Raster Dataset dialog Info... button once again open the
Dataset Information dialog box.
32
Using GeoTIFF/TFW images
The image now has Datum, Projection and Cell Size information,
which ER Mapper extracts from the TFW file.
The TFW file contains the following information
•
The X and Y cell size dimensions
•
The real world coordinates of the image reference point, which is
located in the middle of the top left cell.
TFW files do not contain Datum and Projection information, so
ER Mapper defaults to displaying them as ‘WGS84’ and ‘LOCAL’.
Also the cell sizes could be in feet whereas ER Mapper always
assumes them to be in meters.
12. Click on the Dataset Information dialog Close button.
13. Click on the Raster Dataset dialog Cancel button to close the
dialog.
Open the Change
Datum/Projection/Cell
size wizard
1. From the Toolbars menu, select the Batch Processing toolbar.
2. Click on the
button to open the Change
Datum/Projection/Cell Size wizard.
The first page of the wizard explains the purpose and usage of the
wizard. You can obtain more information by clicking on the
Additional help button.
3. Click on the wizard Next> button.
Using GeoTIFF/TFW images
33
4. Click on the file chooser button
on the Input file field.
5. On the Select File dialog, select ‘GeoTIFF/TIFF(.tif)’ in the Files of
Type field.
6. From the Directories menu (on the Select File dialog), select the
\examples path.
7. Double-click on the ‘Functions_and_Features’ directory to open it.
8. Double-click on the ‘airphoto_tutorial’ directory.
9. Double-click on the image dataset ‘1_3_rect.tif’ to select it.
10. Select ‘This image only’ for the search criteria.
You can do batch conversions on a number of image files in the same
directory by selecting the appropriate search criteria. This would be
particularly useful if you intend mosaicing a large number of images,
and need to edit their georeferencing information first.
11. Click on the wizard Next> button.
The next wizard page contains the existing image information
contained in the TFW World file associated with the image. The
wizard does not change the TFW file in any way, but rather creates
a .ers header file with the new information.
ER Mapper will ignore the World (TFW) file if a .ers header file
already exists.
12. Enter the changes to be included in the .ers header file.
34
Using GeoTIFF/TFW images
13. Click on the chooser
button on the Datum field.
14. In the Datum Chooser dialog box, double click on the ‘NAD83’ entry
to select it.
15. Click on the chooser
button on the Projection field.
16. In the Projection Chooser dialog box, select the ‘utm’ projection
type from the left-hand list, and then double click on the ‘NUTM11’
projection in the right-hand list to select it.
Using GeoTIFF/TFW images
35
17. Select ‘Do not change’ in the Cell Size field.
The sizes are already in meters, so there is no need to convert them.
If we were using a foot-based projection, the sizes would most likely
have been in feet, and would thus have had to be converted to
meters.
ER Mapper always interprets the units to be meters. If you select
the Convert to meters option, the wizard will divide the
displayed value by 3.048 so that it is correct in meters. The
Convert to feet option reverses the calculation.
18. Click on the Next> button, and then click Next> again on the
Confirm changes page.
The wizard will create a .ers header file for the TIFF image and edit
it to include the datum, projection, cell size and cell size unit values
you entered.
19. Click Close on the status dialog, and Finish on wizard page.
When you open the image in ER Mapper, ER Mapper will ignore the
TFW World file in favor of the .ers header file. You can now use
ER Mapper to process the image, and then save it in any of the
supported formats including GeoTIFF or ECW compressed.
ER Mapper does not change the TFW World file. It creates a new
.ers header file for use within ER Mapper, and then uses the
information in the .ers header if the image is saved with
georeferencing information.
Open the TIFF image
We will now open the TIFF image in ER Mapper.
1. Click on the Open button on the Standard toolbar.
36
Using GeoTIFF/TFW images
2. On the Open dialog, select ‘GeoTIFF/TIFF(.tif)’ in the Files of
Type field.
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 ‘airphoto_tutorial’ directory.
6. Double-click on the image dataset ‘1_3_rect.tif’ to load it into an
algorithm.
ER Mapper will display the image.
View the TIFF image
georeferencing
information
1. On the ER Mapper Common Functions toolbar, click on the Load
Dataset
button.
2. On the Raster Dataset dialog, select ‘GeoTIFF/TIFF(.tif)’ in the Files
of Type field.
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 ‘airphoto_tutorial’ directory.
6. Click on the image dataset ‘1_3_rect.tif’ to select it. Do not load it.
7. Click on the Info button to display the Dataset Information dialog
box.
Using GeoTIFF/TFW images
37
Notice that the Geodetic Datum and Map Projection fields are what
you entered with the Change Datum/Projection/Cell size Wizard.
ER Mapper extracts this information from the .ers header file.
8. Click on the Dataset Information dialog Close button and the
Raster Dataset dialog Cancel button.
Save the TIFF image as
GeoTIFF
You will now save the TIFF image in GeoTIFF format. ER Mapper will
extract the georeferencing information from the .ers header file and
embed it in the GeoTiff image data file.
1. From the File menu, select Save As....
2. On the Save As... dialog box, in the Files of Type: field, select
‘GeoTIFF/TIFF’.
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 ‘airphoto_tutorial’ directory.
6. In the Save as: field, enter “1_3_rect_geo.tif”. (The ‘.tif’ extension
will be added automatically if you omit it.)
7. Click OK to close the Save As... and open the Save As
GeoTIFF/TIFF dialog box.
8. On the Save As GeoTIFF/TIFF dialog box, click on the Defaults
button.
This ensures that the settings are the same as those of original TIFF
image.
9. Click on the Options... button to open the GeoTIFF Options dialog
box.
10. Select the Save Geotiff Information option and click on the OK
button.
This specifies that the georeferencing information in the .ers header
file is to be included in the image data file. If you do not select this
option, the image will be saved as a normal TIFF file. Any
georeferencing information would then have to be included in a
separate TFW World file.
38
Using GeoTIFF/TFW images
11. Make sure that the Maintain aspect ratio and Delete output
transforms options are both selected in the Save As
GeoTIFF/TIFF dialog box.
Click on the OK button.
ER Mapper indicates the progress of the save via a status dialog box.
12. Click OK in the confirmation dialog.
Display the GeoTIFF
image
1. On the Standard toolbar, click the Open
button.
2. On the Open dialog box, in the Files of Type: field, select
‘GeoTIFF/TIFF’.
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 ‘airphoto_tutorial’ directory.
6. Double-click on the image file ‘1_3_rect_geo.tif’ to load it.
ER Mapper will display the same image as before.
View the GeoTIFF
georeferencing
information
1. On the ER Mapper Common Functions toolbar, click on the Load
Dataset
button.
2. On the Raster Dataset dialog, select ‘GeoTIFF/TIFF(.tif)’ in the Files
of Type field.
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 ‘airphoto_tutorial’ directory.
6. Click on the image dataset ‘1_3_rect_geo.tif’ to select it. Do not load
it.
Using GeoTIFF/TFW images
39
7. Click on the Info button to display the Dataset Information dialog
box.
Notice that the Geodetic Datum and Map Projection fields are the
same as those of the original TIFF image. There is also no
‘1_3_rect_geo.ers’ header file, so ER Mapper extracts this
information from the GeoTIFF file.
8. Click on the Dataset Information dialog Close button and the
Raster Dataset dialog Cancel button.
Close all windows
1. Close all image windows using the window system controls:
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...
40
After completing these exercises, you know how to perform the following tasks in
ER Mapper:
•
Use the Change Datum/Projection/Cell size Wizard to create and
edit a .ers file
•
Save the TIFF image with georeferencing information in GeoTIFF
format.
Using GeoTIFF/TFW images
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 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.
This geometric correction process is known as rectification.
The ER Mapper Ortho and Geocoding Wizard can perform four
different types of rectification.
•
Triangulation
•
Polynomial
•
Orthorectification using Ground Control Points (GCPs)
•
Advanced Orthorectification using exterior orientation
The method you use, with its corresponding degree of accuracy,
depends on the amount of information you have about the sensor
equipment, the platform it is mounted on and the terrain being
scanned or photographed.
For airphotos it is preferable to use Orthorectification rather than
Triangulation and Polynomial. For this reason, this chapter
concentrates on Orthorectification.
Image orthorectification
41
Some airphoto datasets have already been rectified before being
opened in ER Mapper. These include orthorectified datasets such
as the USGS Digital Ortho Quad (DOQ) series, GeoTIFF images
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).
Ground Control
Points
A common way to rectify an image 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.
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 image
About
orthorectification
42
•
The raw image is simply a digitized airphoto that has been
imported into ER Mapper
•
The reference image is any other dataset, hardcopy map, or set
of known coordinate points that can be used to correct the raw
image. 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).
Orthorectification is more accurate than Linear or Polynomial
rectification because it corrects local and global distortions in the
image by adjusting for camera characteristics, platform positions
and terrain details. This is particularly important for airphotos
because they are generally of a higher resolution than satellite
images. The following pictures demonstrate how airphoto images
can be distorted by variations in terrain, and the effects of height
correction in orthorectification.
Image orthorectification
It is possible to use Polynomial and Triangulation rectification to
correct for terrain variations, provided you choose enough GCPs. The
following table shows the numbers of GCPs you would require for
Polynomial rectification.
Polynomial
GCP Requirements
order
Minimum
Recommended
Linear
3
6
Quadratic
6
12
Cubic
10
20
nth
Not possible
Not possible
Terrain type
From the table you can see that, if the terrain is generally flat, you
can use Linear order Polynomial rectification with 6 GCPs. For
satellite images covering larger areas, where you need to correct for
the earth’s curvature, you will need Quadratic order Polynomia1
rectification with 12 GCPs. For gently undulating terrain you should
use cubic order polynomial rectification with a recommended 20
GCPs. Selecting this number of GCPs per image is time-consuming
process that still does not rectify images with real-world type terrain.
Triangulation rectification does allow you to rectify images with more
rugged terrains, but can require hundreds of manually selected GCPs
per image.
Image orthorectification
43
Orthorectification, on the other hand, requires you to enter only 4 to
6 GCPs, and to identify the positions of fiducial points on the edges
of the image. You have to supply the terrain details to the ER Mapper
Geocoding Wizard in the form of a DEM (Digital Elevation Model). If
the terrain is relatively flat, you can use an average height value.
The ER Mapper orthorectification does not correct images for the
curvature of the earth. This is only significant for individual
images of areas that are longer than 20km, which precludes
most airphotos.
DEM file
A DEM is an image that comprises regularly gridded Z (height) data.
If the height information is only available as contours, breaklines or
XYZ ascii files, you can use the ER Mapper Gridding Wizard to create
a DEM. Refer to the ER Mapper User Guide for information on the
Gridding Wizard. The accuracy of the orthorectification depends on
the resolution of the DEM. The following table gives a rough guide to
the DEM resolutions required:
Airphoto scale
Required accuracy
Height data
1:10,000 - 1:15,000
1 - 2 meters
1 - 2 meter contours
1:20,000 - 1:30,000
2 - 5 meters
5 meter contours
1:40,000+
5+ meters
10 meter contours
Camera file
ER Mapper stores camera characteristics in a camera file for use by
the Geocoding Wizard. The camera file information is derived 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. ER Mapper provides
a Camera Wizard which steps you through the process of creating a
camera file.
To create a camera file you require to have the following information
and this is normally provided by the company which acquired the
aerial images:
Camera Identification: Manufacturer, model, lens serial number and
date calibrated.
Camera attributes: Focal length, X and Y offset to principal point, and
location of fiducial points.
44
Image orthorectification
About fiducial points
Fiducial points are marks (a small circle with a cross inside) inserted
around the edges of airphotos by metric cameras. These fiducial
points, either at 4 corners (4 fiducial points) or at 4 corners and 4
middle points at the edges of the airphoto (8 fiducial points) are used
to accurately relate the airphoto to the principal point which is the
center of the airphoto. The positions of these fiducial points are
adjusted in the aerial camera so that the intersection of lines through
opposite fiducial marks identifies the principal point on the focal
plane.
It is important to correctly position the airphoto so that fiducial
points are correctly related to the principal point (explained later in
this chapter). In the example used in the exercises in this chapter,
the dark strip (where camera and flight information are mentioned)
of the airphoto is on the left side meaning the flight direction is from
left to right and the fiducial points at the 4 corners are defined as
below:
•
Bottom-Right corner = Fid1(+x; -y)
•
Bottom-Left corner = Fid2 (-x; -y)
•
Top-Left corner = Fid3 (-x; +y)
•
Top-Right corner = Fid4 (+x; +y)
If the flight direction is from right to left, as shown above, then the
positions of the fiducial points at the 4 corners, to include in the
camera file for the orthorectification process, are defined as below:
Image orthorectification
•
Bottom-Right corner = Fid3 (-x; +y)
•
Bottom-Left corner = Fid4 (+x; +y)
•
Top-Left corner = Fid1 (+x; -y)
•
Top-Right corner = Fid2 (-x; -y)
45
Similarly, the values for the middle top and middle bottom and
middle left and middle right would be interchanged. In effect, in
cases where the flight direction is from right to left, you need to
rotate the airphoto clockwise 180 degrees to that the data strip will
be on your left. In this position the North direction will be top-bottom
-Y axis.
While carrying out orthorectification you do not have to select
the ‘All 8’ option which uses all eight fiducial points marked by
the camera. You can reduce the amount of work by selecting
either the ‘4 Middle’ or ‘4 Corners’ option.
Advanced
orthorectification
In the case of Advanced Orthorectification, the image data supplier
provides exterior orientation values that describe the exact position
of the aircraft at the time the image was taken, and how this relates
to the image. This does away with the necessity to plot Ground
Control Points. The following exterior orientation parameters are
specified:
•
Attitude omega: The tilt angle (roll) of the aircraft; i.e. the
•
Attitude phi: The swing angle (pitch) of the aircraft; i.e the
•
Attitude kappa: The azimuth angle (yaw)of the aircraft; i.e the
rotation about the Z axis.
•
rotation about the X axis (direction of travel).
rotation about the Y axis.
Exposure center XYZ: The co-ordinates of the exposure center of
the image.
If you do not have the exterior orientation parameters, then you
have to specify about 4 to 6 GCPs for the Geocoding Wizard to
compute them.
The format of exterior orientation parameters generated by
different photogrammetry devices can vary considerably from
device to device, and you might need to modify them to be
compatible with ER Mapper.
Input data requirements
46
You must have the following information available to able to use the
Geocoding Wizard to orthorectify an image:
•
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)
Image orthorectification
•
GCPs referenced by their XYZ coordinates.(Not required if you
have the exterior orientation parameters.
The diagram below illustrates the required inputs for
orthorectification.
The Geocoding Wizard only supports images in ER Mapper
Raster Dataset format. If the image is in another format, then
you should either save it in ER Mapper Raster Dataset format or
use the import utilities to import it as an ER Mapper Raster
Dataset.
Hands-on
exercises
What you will
learn...
These exercises give you practice using ER Mapper’s Geocoding
Wizard to orthorectify an airphoto image.
After completing these exercises, you will know how to perform the following tasks in
ER Mapper:
Image orthorectification
•
Use the Geocoding Wizard to orthorectify an airphoto
•
Use the Camera Wizard to create a Camera File from a calibration
report
47
Before you
begin...
•
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 airphoto image of San Diego taken in 1997. 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
button in the
Common Functions toolbar.
The Geocoding Wizard will open with the 1) Start tab selected.
48
Image orthorectification
2. Click the Load Algorithm or Dataset
button in the Input
file: field to open the file chooser.
3. From the Directories menu, select the path ending with the text
\examples.
4. Select the directory ‘Applications\,Airphoto\1_Geocoding’ and then
double-click 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 could have chosen the Orthorectify using exterior
orientation option.
6. Select the 2) Ortho Setup tab.
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.
Image orthorectification
49
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.
7. 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.
8. Click on the Load input DEM File
button to open the file
chooser.
9. 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.
10. Click on the Camera Wizard
button to open the Camera
Wizard dialog.
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.
50
Image orthorectification
2. Click on the Next> button to go to the Camera identification page.
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:3 Year: 2006
4. Click on the Next> button to go to the ‘Camera attributes page’.
Image orthorectification
51
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:
•
X offset to principal point: 0
•
Y offset to principal point: 0
152.793
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 offcenter, and this is represented by the X and Y offsets to the principal
point. The diagram below illustrates this by exaggerating the lens
distortion.
52
Image orthorectification
While the focal length information is critical, you can generally
set the principal point offsets to 0 because lens distortion will be
negligible compared to that introduced by the scanner.
6. Click on the Next> button to go to the ‘Number of Fiducial points’
page
See section About fiducial points regarding the right orientation of
your airphoto depending on whether the flight direction was
from left to right or right to left.
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.
Image orthorectification
53
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:
54
•
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
Image orthorectification
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. The
flight direction is not always from left to right (as in this exercise,
with data strip on left side of the image and North direction in
bottom-top +Y axis). If the flight direction is from right to left
the data strip will be on the right. Then you need to rotate the
airphoto clockwise 180 degrees so that the data strip will be on
your left. In this position the North direction will be top-bottom
-Y axis. In this position you specify the fiducial points at 4
corners and 4 middle points (Top-Left (+x -y); Top-Right (-x y); Bottom-Left (+x +y); Bottom-Right (-x +y). Likewise,
Middle-Left (+x+y); Middle-Right (-x+y); Middle-Top (-x-y) and
Middle-Bottom (+x+y)) in the Camera File.
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 ‘functions_and_features\airphoto_tutorial’, and
then enter ‘camera_<your initials>’ in the Save as: field.
14. Click on the OK button to return to the Camera Wizard.
Image orthorectification
55
15. The file name and directory you entered should now be displayed in
the Camera file: field.
16. Click on the Finish button to return to the Geocoding Wizard.
17. Click the Load Camera File
button in the Geocoding Wizard
Camera file: field to open the file chooser.
18. From the Directories menu, select the path ending with the text
\examples.
19. Select the directory ‘functions_and_features\airphoto_tutorial’, and
then double-click on the ‘camera_<your initials>’ file you saved.
20. Click on the 3) Fiducial Point Edit tab.
Edit the fiducial points
This wizard page enables you to enter the locations of the fiducial
points on the image into ER Mapper.
Images scanned by lower quality scanners often have fiducial
points that are difficult to see. It often helps to increase the
image contrast before orthorectifying them.
ER mapper opens two image windows one in OVERVIEW ROAM
mode, and the other in ZOOM mode.
56
Image orthorectification
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.
4. In the OVERVIEW ROAM window, click on the Fiducial mark on the
top left corner of the image.
Image orthorectification
57
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.
In the case of an airphoto taken from an aircraft flying in the
right to left flight direction, though in the table you would click
Top-Left (under the Name column) in the table, you would
actually have to select the bottom-right corner fiducial point on
the image. This is due to the fact that the image was taken from
an aircraft flying from right to left. Rotate the airphoto 180
degree clockwise and place the dark strip to the left to find out
the corresponding fiducial points to that of the Top-Left name
convention of the Geocoding Wizard. The image bottom-right
corresponds to the Top-Left name convention of the Geocoding
Wizard. The image bottom-left corresponds to the Top-Right
name convention of the Geocoding Wizard. The image top-right
corresponds to the Bottom-Left name convention of the
Geocoding Wizard. The image top-left corresponds to the
Bottom-Right name convention of the Geocoding Wizard.
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.
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.
58
Image orthorectification
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 labeled.
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.
Image orthorectification
59
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.
This is the already rectified image containing coordinate information.
Setup parameters for the image rectification
The Datum, Projection, and Coordsys Description fields in the
Output Coordinate Space box show the coordinate system of the
output rectified file. These parameters are included automatically
from the ‘CORRECTED’ (rectified) Airphoto image.
60
Image orthorectification
The Datumshift Code field shows the datumshift method used for
reprojection. Normally, the default method is fine. Click the Change
Datumshift Code button to change it when going from NAD27 to
NAD83(HARN) because the method is specific to each state.
7. Click on the Change button. The ERMapper Coordinate System
Chooser dialog opens showing available coordinate systems.
8. If necessary, change the settings to what is displayed above.
9. Click OK to close the ERMapper Coordinate System Chooser
dialog.
10. Select the Geocoding Wizard 5) GCP Edit tab.
Edit Ground Control
Points
Image orthorectification
61
ER Mapper opens several image windows and dialog boxes. You
should see a screen setup similar to this one:
If your system does not position the windows automatically,
rearrange them as shown above before proceeding.
Pick a GCP in the upper-left part of the reference image
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.
11. 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.
In this example, the reference image extents are, unfortunately,
much smaller than those of the raw image. This means the you
will have to confine the GCPs to fall within the reference image
extents. You should try to select them over as wide an area as
possible, so the first four should be in the four corners of the
reference image.
12. 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
13. 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
62
Image orthorectification
14. Use the two ZOOM windows to adjust the positions of the GCP.
15. Click on the Set Z height from DEM
button to fill in the ‘Height’
field for that GCP.
The wizard will compute the height at that position from the
‘San_Diego_DEM.ers’ DEM file that you specified earlier. The
accuracy of this value depends on the DEM resolution. If you have a
definite height value for that GCP, you can also click on the ‘Height’
field and enter it manually.
You have now picked a GCP in the image.
Pick a second GCP in the
lower-left of the
reference image
1. On the Geocoding Wizard Edit GCP dialog, click the Add new GCP
button.
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
2. 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
3. Use the two ZOOM windows to adjust the positions of the GCP.
4. Click on the Set Z height from DEM
button to fill in the ‘Height’
field for that GCP.
The wizard will compute the height at that position from the
‘San_Diego_DEM.ers’ DEM file that you specified earlier. The
accuracy of this value depends on the DEM resolution. If you have a
definite height value for that GCP, you can also click on the ‘Height’
field and insert it manually.
You have now picked a second GCP in the image.
5. Following the above steps, pick another four GCPs near the upper-
right, lower-right and middle of the reference image.
The more GCPs you pick, the lower the possibility of errors. For
orthorectification you need at least four, with six being the
recommended number.
Image orthorectification
63
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.
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.
64
Image orthorectification
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 time saving facility is available once you have positioned four
points.
13. Click Save on the Geocoding Wizard dialog.
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.
2. From the Directories menu, select the path ending with
\examples.
3. Double-click on the ‘functions_and_features\airphoto_tutorial’
directory to open it.
4. Enter the filename ‘San_Diego_orthorectified’ (start with your
initials), then click OK.
Image orthorectification
65
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
•
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
not visible in the currently active image window.
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.
6. Select the Custom extents option and enter the Easting/Northing
values shown below.
66
Image orthorectification
These values are the extents coordinates for the reference image.
Note that the Latitude and Longitude values change automatically as
you change the Eastings and Northings values.
7. Click on the OK button to exit the Geocode Output Extents dialog
box. and return to the Geocoding Wizard.
8. 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. If you do not enter a null cell value, it will default to that
in the reference image.
Cells having the null cell value will be treated by ER Mapper as
being transparent. This can be very useful if you want to remove
black or white edges around individual images to be mosaiced.
All you have to do is set the null cell value to 0 for black, or 255
for white. You must, however, use this with care because it can
have the undesirable effect of rendering wanted black or white
areas in the image transparent as well.
9. 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.
10. Select Display rectified image to display the image after it is
rectified.
11. 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.
12. When the operation finishes, click OK of the successful completion
dialog.
13. 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.
14. Do not close the image window with the orthorectified image
Evaluate the image
orthorectification
1. On the main menu, click the Edit Algorithm
button to open the
Algorithm window.
2. The Algorithm window shows the Red, Green and Blue layers of the
orthorectified image.
Image orthorectification
67
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.
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:
2. Click Close on the Algorithm window to close it.
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Image orthorectification
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
button in the
Common Functions toolbar.
The Geocoding Wizard will open with the 1) Start tab selected.
2. Click the Load Algorithm or Dataset
button in the Input
file: field to open the file chooser.
3. From the Directories menu, select the path ending with the text
\examples.
4. Select the directory “Applications\,Airphoto\1_Geocoding” and then
double-click 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.
Image orthorectification
69
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.
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:
70
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
Image orthorectification
Field Name
Description
Enter Value
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
483681.44788264
the exposure center of
the image.
Exposure center Y
The Y co-ordinate of
3621463.0778646
the exposure center of
the image.
Exposure center Z
The Z co-ordinate of
3182.9321414632
the exposure center of
the image.
Scale
The scale of the image 0.0000487450079603
expressed as a
98
decimal value.
The following diagram illustrates the relationship between the
parameters.
The Phi, Kappa and Omega values can be negative or positive,
depending on the direction of rotation.
The format of the exterior orientation values is not consistent for
the different devices that can be used to generate them. Before
using them on a set of airphotos, it is advisable to orthorectify
one image using GCPs and then compare the results.
2. Click on the Choose Coordinate System button to open the ER
Mapper Choose Coordinate System dialog.
3. Select the coordinate system as shown below.
Image orthorectification
71
NAD27 / UTM Zone 11N is the coordinate system.
4. Click on the 5) Rectify tab.
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 ‘functions_and_features\airphoto_tutorial’
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.
72
Image orthorectification
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
Evaluate the image
orthorectification
1. On the main menu, click the Edit Algorithm
button to open the
Algorithm window.
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.
Image orthorectification
73
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:
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...
74
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.
Image orthorectification
Reprojecting images
This chapter describes how you would use the ER Mapper Geocoding
Wizard to change an image projection or datum.
UTM and State
Plane projections
An example of where you are likely to want to change the image
projection or datum is in the United States of America where your
airphoto image could have a Universal Transverse Mercator
projection, and you need to mosaic it with images that have a State
Plane projection. You can use the ER Mapper Geocoding Wizard to
change from a UTM to the required State Plane projection.
UTM projections
UTM, Universal Transverse Mercator, is a system of world
coordinates like latitude and longitude, from 80 degrees south
latitude to 84 degrees north latitude, except the measurements are
in meters and UTM lines are orthogonal (are always at right-angles
to each other).
UTM Northing is the distance north from the equator in meters and
Easting is the distance east from central meridians of (60) 6-degreewide zones starting at longitude 180 degrees. Northing is also
divided into 8-degree zones from south to north using the letters C
to X with the equator at M/N, (A,B and Y,Z being reserved for the
UPS coordinate system at the poles).
All measurements are POSITIVE by incorporating a system of "false"
easting and northing by adding an arbitrary number to the central
meridians (500,000m) and 10,000,000m to the distance south of the
equator in the southern hemisphere.
State plane projections
The United States of America use a system of map projections for
various regions. This system is known as the “State Plane Coordinate
System (SPCS)”. The Lambert Conformal Conic projection is the
most widely used, with Transverse Mercator projections being used
for States with predominantly north to south extents. The panhandle
of Alaska is mapped using the Oblique Mercator projection. The
Lambert Conformal Conic is a conic projection usually based on two
standard parallels. It can represent the pole as a single point. This
projection is good for mapping a region, continent and at medium or
large scale.
Older maps are projected onto the Clarke 1866 spheroid with tie
point at Meade’s Ranch in Kansas (datum NAD27). More recent maps
are projected onto the 1983 datum (datum NAD83).
Constraints
Reprojecting images
The Geocoding wizard only supports images in the ER Mapper Raster
Dataset format. Images in other formats, including ECW
compressed, have to be originally imported or saved as ER Mapper
Raster datasets before you can reproject them. Because of the size
of some images, you may have to reproject individual images before
mosaicing them rather than reprojecting the whole mosaiced image.
75
Hands-on
exercises
What you will
learn...
Before you
begin...
These exercises give you practice using ER Mapper’s Geocoding
Wizard to change an image projection from a UTM to a State Plane.i
After completing these exercises, you will know how to perform the following tasks in
ER Mapper:
•
Use the ER Mapper Import utilities to import a TIFF image into
ER Mapper Raster Dataset format.
•
Use the Geocoding Wizard to change an image projection.
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: Import an
image into
ER Mapper
Objectives
Equation 1
Learn how to import a TIFF image into ER Mapper.
For this exercise, you will import the TIFF image, ‘1_3_rect.tiff’, that
you modified in Chapter 3, “Using GeoTIFF/TFW images”. For this reason
you must do that exercise before starting this one.
You have to import this image as an ER Mapper Raster Dataset
because the Geocoding Wizard supports only ER Mapper Raster
Datasets.
Importing a TIFF image
76
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 is in TIFF format. 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:
Reprojecting images
You should have the following three files in your
‘examples\Functions_And_Features\Airphoto_Tutorial’ directory:
1_3_rect.tif
The image data file.
1_3_rect.tfw
The “world” TFW header file originally supplied with the TIFF
image file. This is a text file that contains georeferencing
information, but does not include the datum or projection of the
image.
1_3_rect.ers
An ER Mapper header file created by the Change
Projection/Datum/Cell Size Wizard in the exercise in Chapter
3, “Using GeoTIFF/TFW images”. This header file does include the
image datum and projection, and will be used by ER Mapper rather
than the TFW file.
When you import the TIFF image, ER Mapper will extract the
georeferencing information from the associated TFW file if a .ers
header file does not exist. You would then have to use the
ER Mapper Change Projection/Datum/Cell Size Wizard to
add the datum and projection information, as explained in
Chapter 3, “Using GeoTIFF/TFW images”.
Open the TIFF import
dialog
1. From the Utilities menu, select Import Graphics formats, then
select Raster Translated Images, then Import.
Reprojecting images
77
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 box.
2. Click the file chooser
button on the right side of the Import
File/Device Name field.
The Input File Selection dialog box opens.
3. In the Files of Type: field, select ‘GeoTIFF/TIFF(.tif)’.
4. From the Directories menu (on the Input File dialog), select the
path ending with \examples.
5. Double-click on the directory named ‘functions_and_features’ and
then ‘airphoto_tutorial’ to open it.
6. Double-click on the image file named ‘1_3_rect.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 ‘Miscellaneous’ followed by
‘Tutorial’
10. In the Save As: field, enter the text imported_airphoto then click
OK.
11. Click OK on the Import Raster_Translated dialog.
78
Reprojecting images
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:
•
‘imported_airphoto’ (the binary data file)
•
‘imported_airphoto.ers’ (the ASCII header file)
2: Reproject the
image
Objectives
Learn how to change the image datum and projection.
Open the Geocoding
WIzard
1. Click on the Ortho and Geocoding Wizard
button in the
Common Functions toolbar.
The Geocoding Wizard will open with the 1) Start tab selected.
2. Click the Load Algorithm or Dataset
button in the Input
file: field to open the file chooser.
3. From the Directories menu, select the path ending with the text
\examples.
Reprojecting images
79
4. Select the directory ‘Miscellaneous\Tutorial’ and then double-click on
‘imported_airphoto.ers’ to select it.
This is the image that you imported earlier.
5. Select the Geocoding Wizard Map to map reprojection option.
6. Select the 2)Map to Map Setup tab.
Map to Map setup
The Geocoding Wizard Map to Map Setup page displays the datum
and projection of the input image, and allows you to enter new
settings to which the image can be reprojected.
In this example you are going to change the UTM type projection,
‘NUTM11’ to a State Plane Lambert Conformal Conic (lamcon2) type
projection, ‘L2CAL6F83’. This is ‘NAD83’ datum zone 6 in feet. State
Plane projection projections are bounded by county borders, so the
choice of projection depends on the county covered by the image.
The State Plane System was developed in the 1930s and was
originally based on the North American Datum 1927 (NAD27). While
the NAD27 State Plane System has been superseded by the NAD83
System, maps in NAD27 coordinates are still in use.
1. Click the Choose Coordinate System button in the Output
Coordinate Space section.
80
Reprojecting images
2. Expand the Projected category in the Category column on the left
side of the Coordinate System Chooser.
3. Expand the US-State Plane NAD27-EXACT subcategory.
4. Select NAD83 (ftUS).
5. Select NAD83 / California zone 6 (ftUS) in the Name Column on
the right side of the Coordinate System Chooser.
6. Click OK to save your changes and close the Coordinate System
Chooser.
7. Click on the 3) Rectify tab to go to the final wizard page.
Rectify the image
Reprojecting images
The Geocoding Wizard Rectify page allows you to enter the file name
for the reprojected image. It also displays information about the
image and enables you to change the extents and cell size.
81
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 ‘Miscellaneous/Tutorial’ directory to open it.
4. Enter the filename ‘imported_airphoto_reproj’ in the Save as text
field, then click OK.
You should notice that the reprojected file size is 38.51 MB, which is
approximately the same size as the original image. This is usually a
good indicator that the new projection is compatible with the
original.
5. Leave the Null cell value box unchecked, so that the reprojected
image has the same null value as the original image.
The null cell value is the value that the cell must have for ER Mapper
to interpret it as a null cell (i.e. transparent). This is normally 0. The
Geocoding Wizard gives you the option of leaving the null cell value
to be that of original image (if one exists), or entering a new value.
6. Select the Display rectified image option, and click on the Save
File and Start Rectification button.
This will save the reprojection information in the .ers header file of
the original image, and start the wizard creating the new reprojected
image.
ER Mapper displays a status box that indicates the progress of the
reprojection, and indicates successful completion.
82
Reprojecting images
7. Click OK to close the completion dialog box.
ER Mapper will display the reprojected image,
‘imported_airphoto_reproj’, in an image window.
8. Click on the Geocoding Wizard dialog Close button to exit the
wizard.
Close all windows
1. Close all image windows using the window system controls:
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...
Reprojecting images
After completing these exercises, you know how to perform the following tasks in
ER Mapper:
•
Import a Tiff image in ER Mapper
•
Change the image project from a UTM to a State plane
projection.
83
84
Reprojecting images
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
•
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).
Image display priority
By changing the order of the algorithm layers containing the
separate images, you can control image display priority (that is,
which images appear on top of others in the event of overlap).
Images loaded into the uppermost layer of any type always appear
on top of any other images in layers below where overlap occurs
between them.
Assembling image mosaics
85
Images 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 image, you can display the entire extents of the high
resolution image by putting its layer(s) on top in the algorithm layer
list.
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 grayscale and RGB image
mosaic algorithms.
What you will
learn...
After completing these exercises, you will know how to perform the following tasks in
ER Mapper:
The ER Mapper Image Display and Mosaic Wizard provides the
easiest and most efficient way of mosaicing images, and should be
used where possible.
•
Before you
begin...
Use the Image Display and Mosaic Wizard to speed creation of
grayscale 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
mosaics
automatically
Objectives
Learn how to speed the creation of grayscale and RGB mosaic algorithms using the
Image Display and Mosaic Wizard.
Start the Image Display
and Mosaic wizard
1. On the Common Functions toolbar, click the Image Display and
Mosaic Wizard
button.
The Select files to display and mosaic page of the Image Display and
Mosaicing Wizard opens
2. Click the Load Image
86
button.
Assembling image mosaics
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 ‘airphoto_tutorial’ directory.
6. Double-click on the image dataset ‘1_4_rect.ecw’ to select it.
This is a 1GB high resolution airphoto of San Diego that has been
orthorectified and compressed with ER Mapper ECW compression.
You can save disk space by compressing the individual images
before mosaicing them.
7. 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.
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.
Assembling image mosaics
87
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, but can have different
cell sizes. They are also in the same directory.
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.
1. Select the Feather blend mosaic between images options. Do
not select the other two options.
It is not necessary to define and use stitch regions here. You will see
later that the Image Balancing Wizard does this automatically.
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 grayscale display option and Manually select display
method properties.
88
Assembling image mosaics
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
grayscale.
1. Select band ‘B1:Red’ from the drop-down menu.
This specifies that the Red band of the image is to be displayed as
grayscale.
2. Click on the Next> button to go to the next wizard page.
Mosaic and display the
images
The wizard searches the current directory and mosaics and displays
the following images:
•
1_4_rect.ecw
•
1_5_rect.ecw
•
2_6_rect.ecw
•
2_7_rect.ecw
3. For the moment, leave the Image Display and Mosaic Wizard
has finished page open.
4. Drag the lower border of the image window downward about 50%.
5. 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 airphoto
images.
6. On the main menu, click the Edit Algorithm
button.
The Algorithm dialog box opens.
Assembling image mosaics
89
You now have a algorithm that displays band 1 of each dataset as a
grayscale image mosaic.
7. 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 left 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’ (‘1_4_rect.ecw’) 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 ‘1_4_rect.ecw’ dataset
(but also displays part of the lower dataset that occupies the same
extents).
90
Assembling image mosaics
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.
4. Right-click in the image window again, and select Zoom to All
Datasets from the Quick Zoom menu.
ER Mapper zooms out to display the full extents of the mosaiced
image.
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 grayscale mosaiced image as an RGB image.
Change the image display
method
1. On the Image Display and Mosaic Wizard has finished wizard
page, which should still be open, click on the Back to Change
display method button.
This will return you to the Select display method 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.
Assembling image mosaics
91
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. Leave the Image wizard has finished wizard page open for the
moment.
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.)
3: Adding a
GeoTIFF image to
the mosaic
Objectives
Learn how to add an additional image to the mosaic.
We use the Image Display and Mosaicing wizard to add a GeoTIFF
image to the mosaic.
Add an extra image to the
mosaic
The ‘airphoto_tutorial’ directory contains the image file that you
saved in GeoTIFF format in a previous exercise. The Display and
Mosaic Wizard did not automatically include it in the mosaic because
it is in a different format to the other image files. You can, however
manually add it to the mosaic.
This procedure is included to demonstrate that it is possible to
mosaic images with different file formats. In this case it would
have been better to have compressed the GeoTIFF image with
ECW v2 first, and then have let the wizard automatically include
it in the mosaic with the other ECW v2 compressed images.
1. On the wizard dialog, select the Back to Change file button.
The wizard will go back to the file input page.
92
Assembling image mosaics
2. Click on the <Back button to go back one page.
3. Select the Add more to this window option, and then click on the
Next> button.
4. On the Select files to add to display wizard page, click on the file
chooser button.
5. In the ‘airphoto_tutorial’ directory, double-click on the
‘1_3_rect_geo.tif’ file to select it.
6. Make sure that only the Manually set display method option is
selected before clicking on the Next> button.
The wizard will add the ‘1_3_rect_geo.tif’ image to the mosaic, and
automatically set the display mode to Red Green Blue.
Assembling image mosaics
93
7. Click on wizard Finish button to close it.
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. Open the ‘functions_and_features\airphoto_tutorial’ directory.
5. In the Save As: text field, type the following filename:
airphoto_mosaic
This name denotes that it is a mosaic of airphotos.
6. Click OK to save the algorithm.
Your mosaic algorithm is now saved to an algorithm file on disk.
7. Click Finish on the Image Display and Mosaic Wizard has
finished wizard page.
Close all image windows
and dialog boxes
1. Close the image windows by selecting Close from the File menu.
94
Assembling image mosaics
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:
Assembling image mosaics
•
Use the Image Display and Mosaic Wizard to speed creation
of grayscale and RGB mosaics
•
Turn images on or off in a mosaic
•
Add images to mosaics
95
96
Assembling image mosaics
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.
Hands-on
exercises
What you will
learn...
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.
After completing these exercises, you will know how to perform the following tasks in
ER Mapper:
•
Before you
begin...
Use the Image Balancing Wizard to balance and color match an
airphoto 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: 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.
2. From the Directories menu, select the \examples path.
3. Open the ‘functions_and_features\airphoto_tutorial’ directory.
4. Double-click on the algorithm ‘airphoto_mosaic.alg’ to open it.
This is the algorithm that you saved in the previous exercise. It
comprises one GeoTIFF and four ECW compressed airphotos of San
Diego that were mosaiced using the Image Display and Mosaic
Wizard.
Open the Image Balancing Wizard for Airphotos
1. Click on the Image Balancing Wizard for Airphotos
button
on the Common Functions toolbar to open the wizard.
Color balancing image mosaics
97
The wizard processes the currently active image window
2. Select the Images have changed and need reanalyzing option.
The wizard 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 prior to 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.
ER Mapper creates header (.ers) files for the images to store the
analysis information if they do not already exist.
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Color balancing image mosaics
Select how to balance the images
In addition to color balancing, you also have a number of options for
displaying the image. These are described below:
Original
Remove any color balancing and display the
unbalanced images.
The white boxes in the diagram show the
extents of the individual images with their
black edges removed.
Balanced
Display the balanced images but do not clip
edges.
Balanced
Display the balanced images and remove the
with no
black or white edges.
black/white
It is preferable not to select this option when
edges
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.
Some images are supplied with their
black edges already removed, in
which case it is not necessary to
select this option.
Balanced
with clip
regions
When mosaicing images, compute clip
regions to hide the edges between images.
Clip regions are areas of overlap that are
trimmed off to create a seamless join. 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.
Color balancing image mosaics
99
Correct for
If your image has large areas with low
water areas. contrast, such as water, they could be
discolored by the balancing process. Select
this option to prevent this happening.
Show clip
regions as
vector
overlays
Outline the clip regions in 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. Select ‘None’ in the Blue Haze Filter field.
The Image Balancing Wizard uses this field for handling effects
caused by having a “blue haze” filter on the camera lens at data
capture time.
4. 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 tempbalance 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.
100
Color balancing image mosaics
For this exercise we will match the color to the ‘1_3_rect_geo.tif’
image.
1. Select the Match colors to individual file 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 ‘1_3_rect_geo.tif’.
3. Select the Apply 99% clip option to improve the contrast, and click
on the Next button.
Generally you would not select the Apply 99% clip option if you
are going to compress the image, because you usually want the
compressed image to be the same as the original.
The wizard will display the status of the color matching which could
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
button
on the process diagram.
This will open the Formula Editor.
Color balancing image mosaics
101
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 areas of
the image that fall within the automatically created clip region,
‘Image Clip’. Raster cells 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.
Note that the formula applied is the same as that for the top red
layer.
4. Click three times more on the Red button, to move to the three lower
red layers.
Not that, in all 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.
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.
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Color balancing image mosaics
8. View the histograms and transforms of all the Red layers by clicking
on the Red
button.
A histogram is a plot showing the range of pixel values on the X-axis
against their relative frequency on the Y-axis.
The transform line maps the data values on the X-axis to the display
brightness on the Y-axis. The Y-axis values will always be 0 to 255,
but the X-axis values depend on the image data. The X-axis values
in our example image are from 0 to 255. A linear transform line will
create an output histogram that is the same as the input. You can
alter this line to create different output histogram, which is shown as
a separate unfilled graph.
To match the colors, the wizard has changed the transform lines so
that the output histograms for each layer are the same. The
following histograms of two of the layers illustrates this.
Color balancing image mosaics
103
9. Repeat the above for the Green and Blue layers.
In all cases note how the wizard has matched the histograms for the
five 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.
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Color balancing image mosaics
3. Open the ‘functions_and_features\airphoto_tutorial’ directory.
4. In the Save As: text field, type the following filename:
airphoto_mosaic_balanced.alg
1. This name denotes that it contains a balanced mosaic of the airphoto
images.
2. Click OK to save the algorithm.
Your balanced algorithm is now saved to an algorithm file on disk.
At this stage, the only disk space being used is that to store the
original one GeoTIFF and four compressed images. It is now
possible to save the balanced mosaic in any image format,
including ECW compressed.
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:
Color balancing image mosaics
•
Use the Color Balancing Wizard for Airphotos to balance and color
match the mosaiced images.
•
Open the Formula Editor to view the formula that the wizard
applies to the layers.
•
Open the Transform dialog to view the histograms and
transforms.
105
106
Color balancing image mosaics
Compressing images
This chapter shows you how to save your large mosaic as a
compressed image.
About Enhanced
Compression
Wavelet (ECW)
compression
ER Mapper compresses images using wavelet compression
technology that 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.
Hands-on
exercises
What you will
learn...
These exercises show you how to save images in ECW compressed
format using the Compression Wizard.
For these exercises, we will be using the airphoto mosaic algorithm
we created and color balanced previously.
After completing these exercises, you will know how to perform the following tasks in
ER Mapper:
•
Before you
begin...
Use the Compression Wizard to save images in ECW compressed
format.
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: Saving a
compressed
image to disk
Objectives
Compressing images
Learn how to save large images in compressed format using the ER Mapper ECW
compression.
107
The compression process could take a long time because of the
large size of the image being compressed. It is suggested that
you time this exercise to allow the compression to take place
overnight.
1. From the main ER Mapper File menu, select Save as a
Compressed Image.
The Compression Wizard will open.
Input image to be
compressed
2. 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.
3. In the Input file: field, click the Select File
button.
4. From the Directories menu, select the \examples path.
5. Open the ‘functions_and_features\airphoto_tutorial’ directory, then
double-click on the algorithm ‘airphoto_mosaic_balanced.alg’ to
select it.
This is the image mosaic 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.
Compressed image file
name
1. In the Output file: field, click the Select File
108
button.
Compressing images
2. From the Directories menu, select the \examples path.
3. In the Select File dialog, choose ER Mapper compressed images
(.ecw) in the Files of Type field.
4. Open the ‘functions_and_features\airphoto_tutorial’ directory.
5. In the Open: text field, enter the text airphoto_mosaic_compressed
and separate each word with an underscore (_).
6. Click OK on the Select File dialog.
7. 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.
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
1. 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.
2. Click on the Next > button to continue
Compressing images
109
Select Compression ratio
1. Check the Compress for Internet usage box.
This option is for compressed images to be served on an ER Mapper
Image Web Server. 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 Image Web Server, refer to the ER Mapper web
site:
http://demo.ermapper.com
2. If necessary, change the Target compression 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.
110
Compressing images
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.
3. Click on the Finish button to start the compression process.
The compression of an image this large could take a long time
to complete.
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 ‘functions_and_features\airphoto_tutorial’ directory, then
double-click on the algorithm ‘airphoto_mosaic_balanced.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.
Compressing images
111
6. On the main menu, click on the New
button.
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 ‘functions_and_features\airphoto_tutorial’ directory, then
double-click on the file ‘airphoto_mosaic_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.
13. The image will enlarge to fill the image window.
14. Move the image windows so that they are next to one another.
15. 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:
•
After geocoding the images, compress them and store them
on disk.
•
Use the Image Display and Mosaic Wizard to mosaic the
compressed images.
•
Use the Balancing Wizard to balance and color match the
mosaiced image.
•
Use the Compression Wizard to compress the final image.
Close both image windows and dialog boxes
1. Close the image window using the window system controls:
2. Click Close on the Algorithm dialog.
Only the ER Mapper 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:
Compressing images
•
Compressing images
Save the image in compressed format using the ECW
compressor.
113
114
Compressing images
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.
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 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:
Exporting to GIS systems
115
Spatial resolution (cell
size)
Raster formats for GIS
and DMS products
116
•
Zoom into the desired area. You can do this visually by dragging
a zoom box with 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.
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:
•
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.
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® GIS 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® GIS 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.
Exporting to GIS systems
Using compressed
images in GIS
applications
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
What you will
learn...
Before you
begin...
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.
After completing these exercises, you will 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 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. Open the
‘functions_and_features\functions_and_features\airphoto_tutorial’
directory.
Exporting to GIS systems
117
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 display a particular building near
the center 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: 483881
•
Top Left - Northing: 3622145
•
Bottom Right - Easting: 483921
•
Bottom Right - Northing: 3622105
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.
5. Click Close on the Algorithm Geoposition Extents dialog.
118
Exporting to GIS systems
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).
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).
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 labeled ‘Red Layer,’ ‘Green Layer’ and ‘Blue Layer.’
layer labels become band
labels in output dataset
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.
Exporting to GIS systems
119
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.
4. Open the ‘functions_and_features\airphoto_tutorial’ directory
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 . This
creates a full resolution dataset.
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.
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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 Open 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
‘functions_and_features\airphoto_tutorial.’
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.
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 0.06 meter resolution), and file size (about 1.3 Mb in this case).
3. Click Close on the Dataset Information dialog.
4. Click Cancel on the Raster Dataset dialog to close it.
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 0.12 - 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 ‘airphoto_mosaic_balanced’).
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
‘functions_and_features/airphoto_tutorial.’
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6. In the Save As: field, enter the filename project_area_half, then
click OK.
7. This will be the filename for the new UDF dataset.
8. 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.
9. 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.
10. Change the values in the Width and Height fields as follows (the
original values divided by 2 and rounded up):
•
Cells Across (width) = 330
•
Cells Down (height) = 330
11. Click OK.
ER Mapper creates a new half-resolution output dataset on disk.
12. Click OK on the completion dialog.
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.
Exporting to GIS systems
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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
‘functions_and_features\airphoto_tutorial.’
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.
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
button.
2. On the Raster Dataset dialog, click the Info button.
It shows the number of rows and columns is half that of the other
dataset ‘Project_area_full,’ the cell size is approximately 0.12
meters, and the file size is about 326.7 KB (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).
3. 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).
4. 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.
5. Activate the other image window containing the ‘Project_area_full’
dataset.
6. On the Algorithm dialog, turn off the ‘Smoothing’ option.
7. 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.
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8. 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, you must reduce the level of detail in the image.
9. 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.
10. 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.
11. 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.
Exporting to GIS systems
•
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 save 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.
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•
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® GIS 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 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.
3. 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.
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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
‘functions_and_features\airphoto_tutorial.’
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.’
•
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 ESRIcompatible dataset (without actually creating a new image file, only
an ASCII header file.)
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.
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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 airport 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.
3. Enter the following values in the Eastings and Northings Top Left and
Bottom Right fields:
•
Top Left - Easting: 483350
•
Top Left - Northing: 3621735
•
Bottom Right - Easting: 483534
•
Bottom Right - Northing: 3621565
4. Click the Apply button.
ER Mapper zooms to the exact extents you entered, and shows part
of the airport area. This is the image you will save to a TIFF file. The
area displayed is 184 by 170 meters in size (in the Eastings and
Northings Size fields), and 3057 by 2833 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)’.
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3. From the Directories menu, select the path ending with the text
\examples.
4. Double-click on the directory named
‘functions_and_features\airphoto_tutorial.’
5. In the Save As: field, enter the filename project_area_full, then
click OK.
6. This will be the filename for the new tif file.
7. 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 (3067 by
2833). This creates a full resolution dataset.
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.
8. 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.
9. Click OK.
ER Mapper creates a new output dataset on disk.
10. Click OK on the completion dialog.
Display the new dataset
in RGB
1. On the main menu, select New from the File menu.
1. 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
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129
5. Double-click on the directory named
‘functions_and_features\airphoto_tutorial.’
6. Double-click on the dataset ‘Project_area_full.tif’.
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 0.06 meter resolution), and file size (about 25 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 ‘airphoto_mosaic_balanced’).
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
‘functions_and_features\airphoto_tutorial.’
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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) = 1533
•
Cells Down (height) = 1416
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.
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
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131
5. Double-click on the directory named
‘functions_and_features\airphoto_tutorial.’
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
button.
2. On the Raster Dataset dialog, click the Info button.
It shows the number of rows and columns is half that of the other
dataset ‘Project_area_full,’ the cell size is approximately 0.12
meters, and the file size is about 6.5 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...
132
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
Exporting to GIS systems
Windows® 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).
To use the OLE capabilities described here, make sure you first
install ER Viewer from the ERDAS installation DVD or download
it from the ER Mapper website at www.ermapper.com.
About ER Viewer
What is OLE?
Windows® applications (OLE)
ER Viewer is a free, easy-to-use image viewing application featuring
interactive roaming and zooming of very large image files. In this
example we use it as an OLE server application to let you view
images inside other 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
•
ER Mapper algorithms
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.
133
Image file
(source file)
image
object
image
object
image
object
spreadsheet
document
word processing
document
presentation
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
134
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:
•
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).
•
Word processing documents, spreadsheets, presentations, and
other applications can all share a single copy of the original
imagery files.
Windows® applications (OLE)
Hands-on
exercises
What you will
learn...
Before you
begin...
•
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 Algorithms to apply
complex processing enhancements that create beautiful images
interactively without changing the original image files.
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.
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 from one area to another
Before beginning these exercises, you must have installed ER Viewer on your system.
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.
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 OLEenabled application. You can use any other OLE-enabled word
processing application if desired (WordPerfect, Framemaker, and so
on).
Windows® applications (OLE)
135
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 Mosaic Unbalanced 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\functions_and_features\airphoto_tutorial’
3. Move the Word application window and the Explorer window side by
side (resize them if needed).
Drag an algorithm image
file into the Word
document
1. Drag the file ‘airphoto_mosaic.alg’ 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 is the image mosaic you
created in a previous exercise.
Zoom and roam using the
ER Viewer toolbar
1. In Word, double-click on the image.
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.
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.
ER Viewer zooms in to display the area you defined with your box.
3. Click the Hand Tool
button, then drag the image.
ER Viewer roams (or pans) to display the adjacent area of the image.
136
Windows® applications (OLE)
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.
Insert the ECW
compressed image into
the document
1. Press Enter twice to create two new lines below the image, then type
the text San Diego Airphoto Mosaic Balanced and Compressed.
2. In the Explorer window, open the ER Mapper home directory, then
open the directory
‘examples\functions_and_features\airphoto_tutorial’.
3. Drag the file ‘airphoto_mosaic_compressed.ecw’ 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 the compressed image mosaic you created earlier. When
compared to the already loaded algorithm, it demonstrates how the
balancing has enhanced the image.
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
compressed image
1. Double-click on the inserted image to display the ER Viewer toolbar.
2. Use the Zoom Tool
to zoom in on the central portion of the
image, then use the Hand Tool
to drag the image and center it.
When finished, click outside the image to return to the word
processing application.
Copy and paste the
compressed image
1. Click once on the compressed image to select it.
2. Press Ctrl+C (or select Edit > Copy) to copy it.
Windows® applications (OLE)
137
3. Press Enter twice to create two new paragraphs in your document.
4. Press Ctrl+V (or select Edit > Paste) to paste the 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.
(Optional) Save your
word processing
document.
1. Save your document, then close the application.
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
138
After completing these exercises, you know how to perform the following tasks in OLEenabled 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
Windows® applications (OLE)
Image Web Servers
Once you have created your airphoto mosaic, you need to consider
how you are going to use them, and how to make them available for
others to use. The Internet has become a popular way of distributing
data. However, the large sizes of airphotos and slow network
connections have precluded using the Internet to distribute them.
Traditionally, vendors have made ‘thumbnail” images, generally in
JPEG format, available on a web site. Users could then order the full
images which would be sent to them on a CD or other suitable
medium. The diagram below illustrates this:
Im a ge
thum bnails
CD
Larg e
Im a ge
Files
Server
ISP
Broadband
link
ER Mapper Image
Web Server
Image Web Servers
Internet
Client
Applic ation
ISP
Dial-up
link
The ER Mapper Image Web Server has changed the way images are
distributed. You can now make your large airphoto mosaics available
for download over the Internet or company intranet. Your users can
also view, zoom into and roam over this image in real time. The
combination of ECW v2 compression technology and the ECWP data
transfer protocol has made this possible.
139
Server side
The Image Web Server is available as an add-on to the Microsoft IIS
(Internet Information Server). For small numbers of clients (less
than 10) or evaluation purposes, you could use the Microsoft PWS
(Personal Web Server). The following diagram shows the server
architecture:
Large
Im age
Files
ECW
c om pression
Client
software
Iim age
Web
Server
IIS/PWS
Network
After installing the IIS or PWS, you can then add the Image Web
Server. As with any other web server you would have to define a
virtual directory for the image storage areas. You would then copy
your ECW compressed images into the server directory.
The Image Web Server also downloads controls to the client when
requested by that client.
For a client application to access an image stored in the Image Web
Server it must specify the URL of the image. The URL must include
the ECW protocol (ecwp) and the address of the Image Web Server.
A typical URL is as follows:
ecwp://earth.ermapper.com/images/hugeimage.ecw
This is embedded in the HTML string. The IIS uses this to detect
which incoming packets are destined for the Image Web Server, and
directs them there.
Client side
The ECW compressed image data is in the form of blocks, which the
Image Web Server can send separately as required.
When a client, in the form of an Internet Explorer or Netscape
browser, accesses an Image Web Server page it needs to have valid
control files installed. These controls enable the client to
decompress, read, and display ECW compressed images. The Image
Web Server can download these to the client when requested.
140
Image Web Servers
The following diagram illustrates the interactions between the client
and the Image Web Server.
Im age
Web
Server
ISP
Internet
Broadband
link
ISP
Dial-up
link
Control
Larg e
Im a ge
Files
Browser
Send image URL to server
Send image information to client
Request blocks not already cached
Send requested bloc ks
Request blocks not already cached
Send requested bloc ks
Close view
When the client application accesses the image via the URL, it sends
a request to the Image Web Server for the information contained in
the image header.
Using this information, the browser can use mouse and key entries
to interactively request the control for a specific view of the image.
On receiving this request, the control checks which image blocks are
required, and requests the Image Web Server to send those that it
has not already cached. It then refreshes the display with the new
information. In this way the user can roam over and zoom into the
image in real time. Only the portion of the image actually being
viewed is decompressed. This minimizes the network bandwidth and
memory requirements for the client PC, with significant gains in
performance.
The control caches all the blocks that it receives and will not access
the server if all the required blocks are already cached. If there is
insufficient room to cache new blocks, it will flush the least recently
used from the cache.
Image Web Servers
141
To access the server from within applications other than the Internet
Explorer or Netscape browsers, you would first have to download the
applicable free plug-in from the ER Mapper web site. You can then
open the image in that application by specifying its URL, just as you
would if you were using a browser. In the case of Microsoft Office®
applications, you must have the free ER Viewer program installed on
your PC. You can then use Windows® OLE (Object Linking and
Embedding) to insert the images into your Office document. As with
the browsers, the plug-in enables you to roam and zoom
interactively with extremely efficient usage of the client PC's
resources.
Hands-on
exercises
What you will
learn...
Before you
begin...
These exercises show you how to open an image served over the
Internet via an Image Web Server. We will access the public
www.earthetc.com Image Web Server to get the image.
After completing these exercises, you will know how to perform the following tasks in
OLE-enabled Windows® applications:
•
Open an image in ER Mapper by specifying its URL
•
Open an image in ArcView® by specifying its URL
Before beginning these exercises, you must have installed ER Viewer and the ArcView®
plug-in on your system. Your PC must also be able to access the Internet.
1: Open an image
in ER Mapper
Objectives
Learn how to open an image served from an Image Web Server in ER Mapper.
Load the image into an
algorithm
1. Click on the Standard toolbar Open
button to display the Open
dialog.
2. Enter ‘ecwp://www.earthetc.com/images/usa/SanDiego3i.ecw’ in
the Open dialog Open: field
142
Image Web Servers
This is the URL for the ‘SanDiego3i.ecw’ image at the ER Mapper
public Image Web Server site. The Enhanced Compression Wavelet
Protocol (ecwp) is used to compress, transfer and decompress the
image.
3. Click OK on the Open dialog.
If your PC has access to the Internet, the image window will display
the compressed ‘SanDiego3i.ecw’ image. You will notice that the
imagery that we have used in previous exercises is a subset of this
much larger image.
4. Re-size the window as required and use the ZoomBox
tool to
zoom into the same part of the image that we have previously been
using.
Zoom into this part
of the image
ER Mapper will request the server for the image blocks pertinent to
your view and display the zoomed image. The server only sends the
blocks required for the view.
If the image appears blurred, try clicking on the Refresh
button. With slow network links ER Mapper might display the
image before it is fully downloaded. Clicking the Refresh
button forces ER Mapper to redisplay the image using all
information cached in the PC.
Image Web Servers
143
5. Click on the Edit Algorithm
button to open the Algorithm
window.
You should notice that the image has been loaded into Red Green
and Blue layers in the algorithm. You can now process the displayed
image using the process diagram buttons.
Saving the image as an
algorithm
1. From the File menu, select Save.
The Save As... dialog box allows you to save your image view in a
number of formats. If you do not want to save the actual image data,
you can save the view and any enhancements by saving the
algorithm.
2. In the Save As dialog select ‘ER Mapper Algorithm’ from the Files
of type list.
3. 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.)
4. Double-click on the directory named ‘functions_and_features’ and
then ‘airphoto_tutorial’ to open it.
5. In the Save As: text field, click to place the cursor, then type the
following name for the algorithm file:
Airphoto_mosaic_balanced_url
6. Click the OK button to save the algorithm and close the dialog.
The algorithm will be saved to disk.
7. Close the image window.
Reloading the algorithm
1. Click on the Open
button on the Standard toolbar to display
the Open dialog box.
2. Select your saved ‘Airphoto_mosaic_balanced_url.alg’ algorithm and
click OK.
ER Mapper will now display the image view from the
www.earthEtc.com Image Web Server. If the view is not cached on
the PC, it will request it over the Internet.
Once again, you may have to click on the Refresh button
a
number of times to get a clear image.
3. Close the image window.
144
Image Web Servers
Using the History file
ER Mapper keeps a list of the five most recently accessed URLs. If
you want to reload the image you can select it from this list instead
of having to type in the URL again.
1. Click on the Open
button on the Standard toolbar to display
the Open dialog box.
2. On the Open dialog box, select the ECW URL History menu.
This will display up to 5 most recently accessed URLs.
3. Select the required URL from the list and click OK.
4. ER Mapper will display the selected image.
5. Close the Image and the Algorithm windows.
2: Open an image
in ArcView® GIS
Objectives
Open a URL file
Learn how to open an image served from an Image Web Server in ArcView® GIS.
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.
1. Open the ArcView® application.
2. On the Project window, click New to open a new View window. (It
should be titled ‘View1’.)
3. Click the Add ECW Image Theme from an Image Web Server
URL
Image Web Servers
button (or select View > Add URL Theme).
145
This should open the Image Theme URL dialog box.
4. Enter the following URL in the URL: field.
ecwp://www.earthetc.com/images/usa/SanDiego3i.ecw
This URL will access the SanDiego3i.ecw compressed image file at
the Earth Resource Mapping www.earthetc.com web site. The
protocol used is ECWP (Enhanced Compression Wavelet Protocol).
5. Click on the OK button.
The image will be loaded as a 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.
6. In the ‘View1’ window turn on the ‘Sandiago3i.url’ theme.
ArcView® GIS displays the San Diego airphoto mosaic image.
Turn on the theme
146
Image Web Servers
7. In the ‘View1’ window, select the ‘Sandiego3i.URL’ theme and then
select Edit > Delete Themes to remove the theme. Answer Yes to
the Delete Themes query.
8. 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.
9. From the History: list select the
‘ecwp://www/earthetc.com/images/usa/Sandiago3i.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 reload the image as a theme in the ‘View1’ window.
10. Click on the Add to Favorites button to open the Add to Favorites
dialog box.
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 ‘sandiego3i.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.
11. 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
13. Select the ‘arcview\averm\urls’ directory if it is not already selected.
Image Web Servers
147
14. Select the ‘sandiego3i.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 the 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.
17. In the ‘View1’ window turn on the ‘Sandiego3i.url’ theme.
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
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
button to improve the image
resolution.
5. Click the Measure
tool, then drag a line to view distances
across an area.
The line length appears in the lower-left corner of the ArcView® GIS
dialog.
Close ArcView® GIS
1. If desired, save your views as an ArcView® project using File >
Save Project As....
148
Image Web Servers
2. Close ArcView® GIS by clicking the Close
button on the
application window or selecting File > Exit.
What you
learned...
Image Web Servers
After completing these exercises, you know how to perform the following tasks:
•
Display an ECW compressed image in ER Mapper via its URL
•
Display an ER Mapper URL file (.ecw) in ArcView® as an Image
Data Source.
149
150
Image Web Servers
Index
A
airphotos
contrast enhancement 20
exporting 107
importing 16
left to right 45
mosaic creation 6, 85
right to left 45
saving and exporting 115
scanning 4
types 3
Algorithm dialog
overview 14
Algorithm Geoposition Extents dialog box
Geolink options 125
algorithms
basic concepts 12, 13
commenting 25
creating automatically 14
creating manually 14
entering description 25
mosaics 97
process diagram 15
saving 25, 94, 104
ArcView
Add to Favorites button 147
Image Theme URL dialog 146
ArcView GIS ER Mapper plug-in
zoom and pan 148
autoclip transform
concept 22
Autodesk products
save/export from ER Mapper 116
Change Projection/Datum/Cell Size wizard 30
Color (RGB) 109
Color Balancing Wizard for Airphotos 97
comments
defining 25
viewing 27
Compression Wizard
Actual compression ratio 111
Compress to Grayscale or RGB 109
saving the compressed image 109
Target Compression ratio 110
contrast enhancement 20
D
data structure diagram 15
displaying datasets 18
displaying images 19
DOQQ 29
E
B
ECW compressed format 29
ECW URL History menu 145
Enhanced Compression Wavelet Protocol
(ecwp) 143
ER Mapper
introduction 3
raster datasets 8
ER Viewer
product capabilities 133
using as OLE server 133
ESRI products
save/export from ER Mapper 116
exporting data 10, 115
resampling cell size 122, 125, 130
to Autodesk products 116
to ESRI .hdr format 126
to MapInfo 116
to TIFF format 128
batch conversions 34
Batch Processing toolbar 33
F
C
camera calibration report 44
Camera file 55
Camera Wizard 50
Camera attributes page 51
Camera identification page 51
Fiducial point offsets page 53
Focal length 52
Number of Fiducial points page 53
X offset to principal point 52
Y offset to principal point 52
151
Fiducial points 45, 56
left to right 45
right to left 45
free imagery plugins for GIS and office applications 107
G
GCP Edit dialog box 64
GCP Setup tab 60
Geocode Output Extents dialog 66
geocoding
advanced orthorectification 46
Index
camera calibration report 44
Geocoding Wizard 41
Auto zoom 62
Exterior Orientation Setup tab 70
Fiducial Point Edit tab 56, 70
GCP Edit tab 61
GCP Setup tab 60
Map to map reprojection 80
Ortho Setup tab 49, 70
Orthorectify using exterior orientation 49,
69
Rectify tab 65, 72
Use a DEM file as height 50
geocoding. See rectification
georeferencing information, embedded in the
data file 29
GeoTIFF 29
GeoTiff format 29
GIS systems
exporting images to 107
raster image formats 116
resampling cell size for 116
subsetting images for 115
using images in 115
graphics formats
exporting to 10
ground control points
overview 42
H
hardcopy printing 10
histogram equalization 23
History file 145
I
Image Display and Mosaicing Wizard 86
image files. See raster datasets
image processing
concepts 11
ER Mapper algorithms 12
image rectification parameters 60
Image Web Server 143
client side 140
server side 140
image windows
loading datasets 18, 19
imagery
sharing via OLE 133
using in office applications 133
Import Raster_Translated dialog 78
importing a GeoTIFF image 76
importing airphoto images 76
152
L
Layer tab 15
layers 15
loading datasets 18, 19
M
map projections. See rectification 41
MapInfo
export from ER Mapper 116
link with ER Mapper 116
Microsoft Office applications 133
mosaicing 6
analyze images 98
capabilities 85
creating algorithms 97
display band 89
display method 88
feathering 99
file types 88
mosaic properties 88
requirements 85
RGB 123 91
setting display priority 85
turning images on/off 90
N
Null cell value 82
O
Object Linking and Embedding (OLE) 133
office applications
using imagery in 133
OLE
drag and drop images 136
overview 133
tutorial 133
orthorectification
Attitude kappa 46, 71
Attitude omega 46, 70
Attitude phi 46, 70
Camera Wizard 50
Exposure center X Y Z 71
exterior orientation 46, 49, 70
fiducial points 58
Focal length 52
Scale 71
X offset to principal point 52
Y offset to principal point 52
P
Postscript files
printing to 10
Index
printing images 10
process stream diagram 15
Projection Chooser dialog box 35
projections
State Plane 75
UTM 75
World (TFW) files 29, 30
World file 29
Z
zooming images
to specific dataset extents 90
R
raster datasets
description 11
mosaicing 97
mosaics 85
raster images
mosaicing 97
rectification
GCP display options 64
S
Save Geotiff Information 38
saving data 115
cropping/subsetting 115
for Autodesk products 116
for MapInfo 116
in UDF format 119
resampling cell size 122, 125, 130
to ESRI .hdr format 126
to TIFF format 128
State plane projections 75
surfaces 15
T
tab pages 15
TIFF format 29
TIFW 30
Transform dialog box 21
transforms
autoclipping 22
histogram equalization 23
viewing 21
U
UDF images 119
UTM projections 75
V
View Mode 15
W
warping images. See rectification 41
wavelet compression technology 107
word processing
inserting images via OLE 133
153
Index
154
Index
155
Index
156
Index
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