ER Mapper Airphoto Tutorial September 2008 This space reserved for graphic. Left and right bleed. Copyright © 2008 ERDAS, Inc. All rights reserved. Printed in the United States of America. The information contained in this document is the exclusive property of ERDAS, Inc. This work is protected under United States copyright law and other international copyright treaties and conventions. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, or by any information storage or retrieval system, except as expressly permitted in writing by ERDAS, Inc. All requests should be sent to the attention of: Manager, Technical Documentation ERDAS, Inc. 5051 Peachtree Corners Circle Suite 100 Norcross, GA 30092-2500 USA. The information contained in this document is subject to change without notice. Government Reserved Rights. MrSID technology incorporated in the Software was developed in part through a project at the Los Alamos National Laboratory, funded by the U.S. Government, managed under contract by the University of California (University), and is under exclusive commercial license to LizardTech, Inc. It is used under license from LizardTech. MrSID is protected by U.S. Patent No. 5,710,835. Foreign patents pending. The U.S. Government and the University have reserved rights in MrSID technology, including without limitation: (a) The U.S. Government has a non-exclusive, nontransferable, irrevocable, paid-up license to practice or have practiced throughout the world, for or on behalf of the United States, inventions covered by U.S. Patent No. 5,710,835 and has other rights under 35 U.S.C. § 200-212 and applicable implementing regulations; (b) If LizardTech's rights in the MrSID Technology terminate during the term of this Agreement, you may continue to use the Software. Any provisions of this license which could reasonably be deemed to do so would then protect the University and/or the U.S. Government; and (c) The University has no obligation to furnish any know-how, technical assistance, or technical data to users of MrSID software and makes no warranty or representation as to the validity of U.S. Patent 5,710,835 nor that the MrSID Software will not infringe any patent or other proprietary right. For further information about these provisions, contact LizardTech, 1008 Western Ave., Suite 200, Seattle, WA 98104. ERDAS, ERDAS IMAGINE, IMAGINE OrthoBASE, Stereo Analyst and IMAGINE VirtualGIS are registered trademarks; IMAGINE OrthoBASE Pro is a trademark of ERDAS, Inc. SOCET SET is a registered trademark of BAE Systems Mission Solutions. Other companies and products mentioned herein are trademarks or registered trademarks of their respective owners. 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........ ........ ........ ........ ........ ........ ........ . . . . . . . . . .6 .. 8 .. 8 .. 8 .. 9 .. 9 . 10 . 10 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 . . . . . . . . . . . . . . . 16 . 17 . 17 . 18 . 19 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 . . . . . . . . . . . . . . . . . . . 20 . 20 . 20 . 22 . 23 . 23 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 . . . . . . . . . . . . . . . . . . . . . . . 24 . 24 . 25 . 25 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 ..... ..... ..... dialog . . . . . . . . . . . . . . . . . . . . . . . . 26 26 26 27 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 . 31 . 33 . 36 . 37 . 38 . 39 . 39 . 40 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 . . . . . . . . . . . . . . . . . . ........ ........ ........ ........ ........ . . . . . . . . . . . . . ........ ........ ........ ........ ........ . . . . . . . 42 . 44 . 44 . 45 . 46 . 46 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 64 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 . . iv Table of Contents 69 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 70 72 73 73 74 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 . . . . . . . . . . . . . . . . . . . . . . . . . . ........ ........ ........ ........ . . . . . . . . . . . . ........ ........ ........ ........ . . . . . . 79 . 79 . 80 . 81 . 83 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 . . . . . . . . . . . 86 . 86 . 88 . 88 . 88 . 89 . 89 . 90 . 90 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 . . . . . . . . . . ........ ........ ........ . . . . . 92 . 92 . 94 . 94 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 . . . . . . . . . . . . . . . . . . . . . . . . . . ........ ........ ........ ........ . 107 . 108 . 108 . 109 . 110 Exporting to GIS systems . . . . . . . . . . . . . . . . . . . . . . . 115 About use in GIS systems . . . Cropping or subsetting images . Spatial resolution (cell size) . . . Raster formats for GIS and DMS . . . . . . . . ......... ......... products . . . . . . . . . . . . . ........ ........ ........ . 115 . 115 . 116 . 116 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 . . . . . . . . . . . . . . . . . . . 126 . 126 . 126 . 126 . 127 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 . . 130 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) . . . . . . . . . . . . . . . . . . . . 133 About ER Viewer . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 What is OLE? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 vi 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) . . 136 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........ ........ ........ ........ . 142 . 142 . 144 . 144 . 145 2: Open an image in ArcView ® GIS . . . . . Open a URL file . . . . . . . . . . . . . . . . . . . . Zoom, pan and measure the image . . . . . . . Close ArcView® GIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........ ........ ........ . 145 . 145 . 148 . 148 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Table of Contents vii 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 • 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 • 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 • land use/land cover mapping • urban and regional planning • environmental assessment • civil engineering • geologic and soil mapping • agricultural and forestry applications • water resource and wetland applications There are generally four types of airphotos in common use, and these are created by using specific types of film in the camera: • 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 • Natural color–often called true color, is also sensitive to the same wavelengths of light as perceived by the human eye. Digitized natural color photos have three separate bands, one each for the blue (0.4-0.5 micrometers), green (0.5-0.6) and red (0.6-0.7) wavelengths of light. They are usually displayed using the RGB color system on a computer to recreate the same colors as on the photo print. Natural photos are commonly used for creating photo maps, or for mapping applications that require discrimination of the color of features. • Infrared–often shortened to “IR,” is sensitive to a range of wavelengths that includes the red, green and near infrared portions of the spectrum. The near infrared wavelengths (0.71.0) 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. 68 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. 98 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. 102 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. 104 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. 120 Exporting to GIS systems 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: Exporting to GIS systems 121 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.’ 122 Exporting to GIS systems 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 123 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. 124 Exporting to GIS systems 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. 125 • 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. 126 Exporting to GIS systems 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. Exporting to GIS systems 127 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)’. 128 Exporting to GIS systems 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 Exporting to GIS systems 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.’ 130 Exporting to GIS systems 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 Exporting to GIS systems 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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