GIToolsV2_tutorial.pdf

Copyright Notice This publication is a copyrighted work owned by: PCI Geomatics 50 West Wilmot Street Richmond Hill, Ontario Canada L4B 1M5 www.pcigeomatics.com The information in this document is subject to change without notice and should not be construed as a commitment by PCI Geomatics. PCI Geomatics assumes no responsibility for any errors that may appear in this document. The software described in this document is furnished under a license and may only be used or copied in accordance with the terms of such license. No responsibility is assumed for the use or reliability of the information that is derived through the use of PCI Geomatics software. Copyright © 2010 by PCI Geomatics. All rights reserved. All copies must contain this notice in its entirety. Trademark Acknowledgements Geomatica, EASI/PACE, ImageWorks, GCPWorks, OrthoEngine, GeoGateway, RADARSOFT, FLY!, PCI Author, PCI Modeler, GeoAnalyst, and Agroma are registered trademarks of PCI Geomatics. InstallShield is a registered trademark of InstallShield Software Corporation. Microsoft is a registered trademark, and Windows is a trademark of Microsoft Corporation. MrSID is a registered trademark of LIZARDTECH Inc. Copyright 1995-2004. All rights reserved. UNIX is a registered trademark of UNIX System Laboratories Inc. All other trademarks and registered trademarks are the properties of their reserved owners.

Table of Contents QUICK GUIDE: GEOIMAGING TOOLS 2.0....................................................... 1

INTRODUCTION.............................................................................................. 1 BACKGROUND ............................................................................................... 1 DATA SOURCES AND PREREQUISITES ..................................................................... 2 SETTING UP YOUR WORK ENVIRONMENT.................................................................. 2

Setting up the work environment............................................................... 2 Creating an ArcCatalog folder connection .................................................... 3 Locating the GeoImaging Tools Image Correction toolbox.............................. 4

LESSON 1: BUILDING A MOSAIC USING A NOMINAL MATH MODEL ..................................... 5 Configuring and running the Ingest Raw Scenes tool..................................... 5 Configuring and running the Write RPDefs tool............................................. 8 Viewing the Images as a Mosaic in ArcMap.................................................10 About the mosaic and the geodatabase......................................................16

LESSON 2: BUILDING A MOSAIC WITH GCPS USING A PROCESS MODEL ............................16 Configuring and running the Raw to RPDef (with GCPs) model ......................17 Viewing the Images as a Mosaic in ArcMap.................................................19 About the mosaic and the geodatabase......................................................24

LESSON 3: COMPARING AND ANALYZING THE RESULTS................................................25 Comparing the alignment accuracy of both math models..............................25 Comparing the feature accuracy of both math models..................................28

The information in this document is subject to change without notice and should not be construed as a commitment by PCI Geomatics. PCI Geomatics assumes no responsibility for any errors that may appear in this document. Copyright © 2010 PCI Geomatics inc. All rights reserved.

1

Quick Guide: GeoImaging Tools 2.0 Introduction PCI’s GeoImaging Tools is a suite of tools that lets you view, process, and analyze your raster imagery within the ESRI ArcGIS environment. With the GeoImaging Tools - Image Correction module, you can read raw satellite images collected from a wide variety of sensors, refine the math model used for geometric correction, and export your data to the ESRI Raster Process Definition (RPDef) format for use in ArcGIS.

This tutorial will demonstrate how to use the image correction tools and process models (workflow) found in PCI’s GeoImaging Tools toolbox. In the first lesson, you will use two of the image correction tools to ingest data with nominal georeferencing and write them to an RPDef file. You will then create a mosaic, add the generated RPDef files to it, and view the results in ArcMap.

In the second lesson, you will use a process model provided with the GeoImaging Tools to ingest the raw data, refine the data with ground control points (GCPs), and generate an RPDef file. You will then create a mosaic, add the generated RPDef files to it, and view the results in ArcMap.

Once the first two lessons have been completed, you will compare and analyze the results achieved.

Background PCI’s GeoImaging Tools – Image Correction modules provides a method for viewing and geometrically correcting raw satellite data in ArcGIS. Satellite data is distributed in a number of different formats, which until now, could not be directly read into ArcGIS. PCI’s Image Correction modules are used to convert raw satellite imagery, from a variety of different sensors, into an RPDef format (Raster Process Definition File), which can be interpreted by ArcGIS applications, such as ArcMap. In addition to providing a means of importing raw satellite data into ArcGIS, PCI’s GeoImaging Tools – Image Correction toolbox includes a powerful set of orthorectification tools, used to geometrically correct raw satellite imagery. When geographically accurate reference data is available, the Refine Raw Scenes with GCPs tool can be used to automatically search both the raw scene and the reference data (Image raster or vector) to collect Ground Control Points (GCPs). GCPs are a set of positions that relate features from a raw scene to the same features in the reference layer. The collection of GCPs is performed automatically and the results are temporarily stored in the ingested PCIDSK (.pix) link file, along with the orbital information and nominal math model. The GCPs are then used to refine the math model, which provides a more accurate geometric correction.

When a series of adjacent images are provided, Tie Points (TPs) can be collected, using the Refine Raw Scenes with Tie Points tool. Tie points are used to better align overlapping features in abutting images. The collection of TPs is performed automatically and the results are stored in the ingested PCIDSK file. The TPs, along with the GCPs, are used to refine the math model, producing an orthorectified image.


2

The Write RPDef tool is used to translate the auxiliary information held in the PCIDSK link file (i.e. GCPs, TPs, orbital information, math model, etc.) to an RPDef file. The information is translated in a way that can be used by ArcGIS applications to import and accurately apply an on-the-fly geometric correction of satellite data.

Data sources and prerequisites This tutorial requires the following software:

• ArcGIS 10.0 with an ArcEditor or ArcInfo license • GeoImaging Tools 2.0

The data required for this tutorial can be downloaded free from PCI Geomatics.

To download the tutorial data:

1. Using your web browser go to the GeoImaging Tools web page at:

http://www.pcigeomatics.com/gitools

2. Locate and download GeoImagingDemo.zip. (under additional information section)

Setting up your work environment Before working with GeoImaging Tools, you will set up your work environment. A well-organized work environment will ensure that all of the input and output data sets are readily accessible.

This tutorial assumes that your working directory is located on the C:\ drive. If you are using another drive, simply replace the ‘C’ at the beginning of each path with the letter of the drive you are using.

Setting up the work environment 1. Locate the GeoImagingDemo.zip file that you downloaded from the PCI public

FTP site.

2. Right-click on the zip file to display the context menu and select Extract All.

3. The Extraction Wizard opens.

4. Change the output directory to C:\GeoImagingDemo and click Next

5. Click Browse and navigate to the C root of your system.

6. Click Make New Folder, and name the new folder GeoImagingDemo.

7. Click OK to return to the Extraction Wizard, then click Next to continue.

8. Click Finish to complete the extraction.

Your working environment should be located at the root of your C drive, organized as follows:

C: - Root of C: drive GeoImagingDemo – Parent Folder

Ingested – Empty folder used to hold the ingested data RawScenes – Contains 10 raw SPOT-4 scenes Reference – Contains 1 DEM and 1 geocoded vector layer representing roads and 1 Landsat-7 mosaic (orthos) RPDefs – Empty folder used to hold output RPDef files


3

Creating an ArcCatalog folder connection 1. Open ArcMap 10 or later

2. Locate the Catalog toolbar, which is generally found on the right hand side of the ArcMap window

3. On the Catalog toolbar, click the Connect to Folder.

4. In the Connect to Folder window, navigate to the GeoImagingDemo directory.


4

5. Click OK.

Locating the GeoImaging Tools Image Correction toolbox 1. Open ArcMap

2. In the ArcGIS Catalog window, expand the Toolboxes branch by double clicking on it or single clicking

3. Double click the Systems Toolboxes branch or single click next to the toolbox to expand it.

4. Locate the PCI GeoImaging Tools – Image Correction toolbox and double-click to expand the toolbox or single click .

You should see four image correction tools and three process models. Two of these tools and one of the models will be used in the following lessons.


5

Lesson 1: Building a mosaic using a nominal math model This lesson provides a basic introduction for using PCI’s GeoImaging – Image Correction tools. You will ingest a series of adjacent SPOT4 images and visualize them as a mosaic, using a nominal math model. The workflow used in this lesson does not collect Ground Control Points (GCPs) or Tie Points (TPs) and therefore, relies on the accuracy of the math model provided in the SPOT4 datasets.

The following steps provide instructions to configure and run the Ingest Raw Scenes tool and the Write RPDefs tool, supplied in the PCI GeoImaging – Image Correction toolbox. This lesson provides a simple workflow used to translate the SPOT4 data into a format that can be read and viewed by ArcGIS applications. Once you have created the RPDef files, which are used to hold the images’ auxiliary information, you will view all 10 SPOT4 scenes in a basic mosaic, using ArcMap.

Note: This example creates a basic mosaic which does not use cutlines or apply color balancing.

Lesson Objectives • Use the basic PCI GeoImaging – Image Correction tools • Ingest raw satellite scenes so that they can be further processed using

other PCI image correction tools • Create RPDef files that hold the (Approximate Geometric Correction) • Add the ingested scenes to a mosaic dataset, which will apply an on-the-

fly geometric correction using a nominal model. • Can use in arc tools

Configuring and running the Ingest Raw Scenes tool 1. In the PCI GeoImaging Tools – Image Correction toolbox, double-click the

Ingest Raw Scenes tool.

The Ingest Raw Scenes window opens.


6

2. Click the Browse button beside the Input Raw Raster Folder box.

The Input Raw Raster Folder window opens.

3. In the Look in list, navigate to Folder Connections and select C:\GeoImagingDemo.

4. Select the RawScenes folder.

5. Click Add.

6. In the Ingest Raw Scenes window, click the Browse button beside the Output Folder (optional) box.

7. In the list of folder connections, select C:\GeoImagingDemo.

8. Double-click the Ingested folder.

9. In the Name box, type Nominal.


7

10. Click Save.

11. Click OK in the Ingest Raw Scenes window.

12. In the process log that appears, look for the line “Scene Ingested Successfully” to ensure that the tool process was successful.

13. Click Close on the Ingest Raw Scenes window.

Summary:

You have now ingested the raw SPOT4 satellite data into a series of linked PCIDSK (.pix) files. The PCIDSK link files do not contain image rasters, but instead point to the SPOT4 image files (IMAG_01.DAT) minimizing data duplication.

In Windows, navigate to C:\...\GIToolsImgCorrDemo\Ingested\Nominal\ to view the PCIDSK link files.

The PCIDSK Link files provide a writable file that can be used to store and refine the math models when GCPs and or TPs are collected. This lesson is limited to preparing


8

and viewing the SPOT4 scenes without refining the math model. Lesson 2 provides step-by-step instructions of how to collect GCPs, necessary to improve the math model.

Configuring and running the Write RPDefs tool 1. In the PCI GeoImaging Tools – Image Correction toolbox, double-click the

Write RPDefs tool.

The Write RPDefs window opens.

2. Click the Browse button beside the Ingested Raster Folder box.


4. Double-click the Ingested folder to open it.

5. Select the Nominal folder, then click Add.

6. Click the Browse button beside the Output RPDef Folder box.

7. Navigate to C:\...\GeoImagingDemo directory

8. Open the RPDefs folder.

9. In the Name box, type NominalRPDefs.

10. Click Save.

11. Click the Browse button beside the DEM Raster (optional) box.

Note: The geometric correction takes into account distortions caused by relief effect. Therefore, an accurate digital elevation model (DEM) of the area being corrected is required.

12. Double-click the Reference folder to open it.


9

13. Double-click the DEM_CDED_50k folder.

14. Select the flt_3x3_dem_ell.flt file.

15. Click Add.

Your Write RPDefs tool settings should look similar to the following:

16. Click OK on the Write RPDefs tool.

17. View the process log to ensure that the RPDefs were generated successfully. Look in the NominalRPDefs directory to see the 10 generated RPDef files.


10

18. Click Close on the Write RPDefs window.

Summary:

You have now successfully created a series of RPDef files, which are used to view and apply the on-the-fly nominal geometric correction to the SPOT4 scenes, in ArcMap.

In Windows, navigate to C:\...\GIToolsImgCorrDemo\RPDefs\Nominal RPDefs\ to view the RPDef files that were just created.

Viewing the Images as a Mosaic in ArcMap Now that you have ingested the SPOT4 data and generated the RPDef files, we will use native ArcMap tools to create a File Geodatabase, add a Mosaic Dataset, add the RPDef files to the Mosaic dataset and view the images as a mosaic in ArcMap.

Creating the File Geodatabase

1. In the Catalog tree, expand the Folder Connections branch.

2. Right-click on C:\GeoImagingDemo and select New > File Geodatabase

A new geodatabase is created.

3. Rename New File Geodatabase to Mosaic GeoDatabase.


11

Creating the Mosaic Dataset

1. In the Catalog tree, right-click Mosaic GeoDatabase and select New > Mosaic Dataset.

2. Ensure that the output location is pointing to Mosaic GeoDatabase.gdb.

3. Type Spot4_Nominal_Mosaic for the name of the mosaic data set.

4. Click the Spatial Reference button beside the Coordinate System box to browse for a coordinate system.

5. In the Spatial Reference Properties window, click Select. 6. Double-click the Geographic Coordinate Systems folder.

7. Double-click the World subfolder.

8. Select WGS1984.prj.

9. Click Add.

10. Click OK on the Spatial Reference Properties window.

The Create Mosaic Dataset window should have the following settings:

11. Click OK on the Create Mosaic Dataset window.


12

12. The SPOT4_Nominal_Mosaic dataset will be added as a layer to the Table of Contents pane, usually located on the left side of the view window.

13. Close the Create Mosaic Dataset window

Adding rasters (RPDef files) to the Mosaic:

1. In the Catalog tree, right-click on the SPOT4_Nominal_Mosaic data set.

2. Select Add Rasters.

The Add Rasters To Mosaic Dataset window opens.


13

3. In the Raster Type list, select Raster Process Definition.

4. Click the Browse button beside the Input box.

5. Navigate to C:\GeoImaging Demo\RPDefs\NominalRPDefs.

6. Select all of the files at once by holding down the Shift key.

7. Click Open.

8. Select the Update Overviews check box.

9. Use the Raster Pyramid Options defaults.

10. Expand the Advanced Options section.

11. Select the Build Raster Pyramids and Calculate Statistics check boxes.


14

The Add Rasters To Mosaic Dataset window should have the following settings:

12. Click OK on the Add Rasters To Mosaic Dataset.

The rasters are added to the mosaic; this may take a few minutes.


15

Viewing the Mosaic

1. In the ArcMap Table Of Contents, right-click the SPOT4_Nominal_Mosaic layer.

2. Select Zoom To Layer.

3. Select the Boundary, Footprint, and Image sublayers to activate them. (if they are not already activated)

The overview of your mosaic should look like this:

4. In the ArcMap window, select File > Save As to save the ArcMap project (.mxd).


16

About the mosaic and the geodatabase

The mosaic you just produced is stored in the Mosaic GeoDatabase.gdb file. The Mosaic GeoDatabase.gdb file references the raw imagery and generates a mosaic on-the-fly; therefore, changing the directory of, or deleting the raw data sets, will adversely affect the mosaic.

The images in the mosaic were geometrically corrected using a nominal math model, which explains why there are misalignments and accuracy issues (Figure below). This method works well when only approximate accuracy is required or when reference data cannot be obtained.

The next lesson will demonstrate a method for improving the alignment and accuracy of the images in the mosaic.

Lesson 2: Building a mosaic with GCPs using a process model In this lesson you will use a pre-constructed process model (Model – Raw to RPDef (With GCPs)), provided in PCI’s GeoImaging Tools - Image Correction Toolbox. The process model will allow you to setup and run the entire workflow within one panel, which includes: Ingesting the image, collecting GCPs, refining the math model and translating the information to a series of RPDef files. You will then add the RPDef files to a mosaic dataset and view them as a Mosaic in ArcMap.

You will be working with the same SPOT4 images used in lesson 1. This will allow you to compare the accuracy between the mosaics produced when a nominal math model is used (lesson 1) as oppose to a refined math model (lesson 2).

Objectives • Use a process model to complete the workflow in one step • Automatically collect GCPs


17

• Create RPDef files that use the GCPs to refine the math model (improved geometric correction)

• Add the ingested (raw) scenes to a mosaic geodatabase, which are geometrically corrected on-the-fly

Configuring and running the Raw to RPDef (with GCPs) model

1. In ArcMap, click the New Project button .

2. Select Blank Map as your template and click OK.

A new empty project is initialized.

3. In the PCI GeoImaging Tools – Image Correction toolbox, double-click Model – Raw to RPDef (with GCPs).

The Model – Raw to RPDef (with GCPs) window opens. It contains all of the required and optional inputs necessary to ingest the raw data, automatically collect the GCPs, refine the math model, and write the output RPDef files.

4. Click the Browse button beside the Input Raw Raster Folder box.


18


6. Select the RawScenes folder and click Add.

7. In the Model – Raw to RPDef (with GCPs) window, click the Browse button

beside the Ingested Folder box.

8. Double-click the Ingested folder.

9. In the Name box, type Refined.

10. Click Save.


beside the Primary Reference Raster box.

12. Double-click the Reference folder.

13. Double-click the oL7 folder.

14. Select Landsat7_Pan_Mosaic.tif. and click Add.

Note: The GCPs are automatically collected using an orthorectified Landsat-7 panchromatic image as the reference raster layer. This process scans both the reference and raw (input) images, applying a correlation technique that places GCPs on pixels where correlations are greater than the Minimum Acceptance Score, which is defaulted to 0.75.

15. In the Model – Raw to RPDef (with GCPs) window, keep the default values for the Search Radius and Line Width parameters.

16. Click the Browse button beside the Output RPDef Folder box.

17. Open the RPDefs folder.

18. In the Name box, type RefinedRPDefs.

19. Click Save.


beside the DEM Raster box.

21. Double-click the Reference folder.

22. Double-click the DEM_CDED_50k folder.

23. Select the flt_3x3_dem_ell.flt file.

24. Click Add.

25. Click OK in the Model – Raw to RPDef (with GCPs) window to run the model and create the RPDef files.

Note: The processing may take a few minutes.

26. In the process log that appears, look for the phrase “Succeeded at” to ensure that the process was successful. Verify that the desired outputs were created; the RefinedRPDefs folder should contain 10 RPDef files.


19

27. Click Close to close the Model – Raw to RPDef (with GCPs) window.

Viewing the Images as a Mosaic in ArcMap Creating the Mosaic Dataset

You can use the same geodatabase that was created in Lesson 1 or create a separate one.

1. In the Catalog tree, right-click Mosaic GeoDatabase and select New > Mosaic Dataset.


20

The Create Mosaic Dataset window opens.

2. Ensure that the output location is pointing to the Mosaic GeoDatabase.gdb.

3. In the Mosaic Dataset Name box, type Spot4_Refined_Mosaic.

4. Click the Spatial Reference button beside the Coordinate System box to browse for a coordinate system.

5. In the Spatial Reference Properties window, click Select. 6. Double-click the Geographic Coordinate Systems folder.

7. Double-click the World subfolder.

8. Select WGS1984.prj.

9. Click Add.

10. Click OK on the Spatial Reference Properties window.

The Create Mosaic Dataset window should have the following settings:

11. Click OK in the Create Mosaic Dataset window.

12. Close the Create Mosaic Dataset window

13. The SPOT4_Refined_Mosaic dataset will be added as a layer to the Table of Contents pane, usually located on the left side of the view window.


21

Adding Rasters (RPDef files) to the Mosaic

1. In the Catalog tree, right-click the Spot4_Refined_Mosaic data set.

2. Select Add Rasters.

The Add Rasters To Mosaic Dataset window opens.


22

3. In the Raster Type list, select Raster Process Definition.

4. Click the Browse button beside the Input box.

5. Navigate to C:\GeoImaging Demo\RPDefs\RefinedRPDefs.

6. Select all of the files at once by holding down the Shift key.

7. Click Open.

8. In the Add Rasters To Mosaic Dataset window, select the Update Overviews check box.

9. Use the Raster Pyramid Options defaults.

10. Expand the Advanced Options section.

11. Select the Build Raster Pyramids and Calculate Statistics check boxes.


23

The Add Rasters To Mosaic Dataset window should have the following settings:

12. Click OK.

The rasters are added to the mosaic; this may take a few minutes.

13. Close the Add Rasters to Mosaic Dataset window Viewing the Mosaic

1. In the ArcMap Table Of Contents, right-click the Spot4_Refined_Mosaic layer.

2. Select Zoom To Layer.


24

3. Select the Boundary, Footprint, and Image sub-layers to activate them (If not

already activated).

The overview of your mosaic should look like this:

4. In the ArcMap window, select File > Save As to save the ArcMap project (.mxd).

About the mosaic and the geodatabase

The mosaic you just generated is stored in the Mosaic GeoDatabase.gdb file that you created earlier. The Mosaic GeoDatabase.gdb file references the raw imagery and generates a mosaic on the fly; therefore, changing the directory of, or deleting the raw data sets, will prevent the mosaic from being rendered.

The images in the mosaic were geometrically corrected using GCPs to refine the math model. As such, the mosaic should have experienced significant improvements in alignment and feature accuracy. We will demonstrate and analyze this in the next lesson.

Once you are satisfied with the mosaic, you can use it in a separate application or export it to an image file (i.e. GeoTIFF). Should you wish to open the mosaic from


25

the geodatabase, simply click the Add Data button and open the Spot4_Refined_Mosaic raster located in the Mosaic GeoDatabase.gdb file.

Lesson 3: Comparing and analyzing the results At this point you have generated two basic mosaics (missing cutlines, color balancing, etc.) and saved the outputs. It is now time to compare the positional accuracy of the two images. When considering positional accuracy, analysts are generally interested in two distinct characteristics: how well abutting images are aligned relative to each other, and the positional accuracy of image features relative to their true position. First, you will inspect the alignment accuracy by zooming in on a distinct feature at the abutment of two images. You will then evaluate the positional accuracy of features relative to their true position using a National Road Network vector layer as the control.

Comparing the alignment accuracy of both math models

1. In ArcMap, click the New Map File button.

2. Select the Blank Map template and click OK.

3. Click the Add Data button.

4. In the Look in drop down list, select C:\GeoImagingDemo

5. Navigate to and open the Mosaic GeoDatabase.gdb file that you created in Lesson 1 (Actually a folder).

6. Use the Shift key to select both the SPOT4_Nominal Mosaic and the Spot4_Refined Mosaic.

7. Click Add.

8. Both mosaics are added to the new project.

9. If SPOT4_Nominal_Mosaic is the top layer skip steps 10 and 11

10. In the ArcMap Table Of Contents, select the SPOT4_Nominal_Mosaic layer.

11. Click and drag the layer so that it is above the Spot4_Refined_Mosaic layer.

12. Click the Go To XY button , located in the ArcMap Toolbar

13. Enter the coordinate Long: -120.652, Lat: 50.741

14. Click the Pan to button

Note: The position of your cursor is displayed at the bottom-right corner of the ArcMap application window.


26

This should center the map space about the coordinate 120.652, 50.741.

15. Once the coordinate point is approximately centered, change the scale of the map space to 1:150,000. To do this, type 1:150,000 in the current scale box on the Standard toolbar, and press Enter.


27

The rendered image should be similar to the following:

16. Toggle the top mosaic (Nominal) layer on and off by selecting and clearing the

SPOT4_Nominal_Mosaic layer check box in the ArcMap Table Of Contents.

The purpose of this comparison is to demonstrate the improved positional accuracy of neighboring images in a mosaic. As mentioned above, there are two main


28

characteristics to look for in a mosaic with regards to positional accuracy: abutting images are well-aligned with one another, and features in the image are accurately georeferenced. This section considers the former, which analyzes the improved alignment of adjacent images when refining the math model using GCPs.

To effectively evaluate the improved alignment when refining a math model using GCPs, it is necessary to zoom in on a distinct feature at the abutment of two images, which is what the above steps accomplished. As you switch back and forth between the SPOT4_Nominal_Mosaic and the Spot4_Refined_Mosaic layers, you should notice that the refined math model resulted in an improved alignment between two images. The following image displays the region around coordinate 120.652, 50.741 at a scale of 1:150,000 for both the SPOT4_Nominal_Mosaic and the Spot4_Refined_Mosaic. This region of interest (ROI) provides a good example of the improved alignment of images in a mosaic when GCPs are used to refine the math model.

Comparing the feature accuracy of both math models

1. Ensure that both mosaic layers are displayed in ArcMap.

2.

3. Click the Add Data button.

4. In the Catalog tree, navigate to C:\GeoImagingDemo\Reference\NRN.

5. Select ROADSEG.shp and click Add.

6. Click Close when warned about the transformation.

Road segments clipped from the National Road Network data set are added to the map.

7. Click the Go To XY button .


29

8. Enter the coordinate Long: -121.234, Lat: 50.587 to center it in the map space.

9. In the current scale box, change the scale to 1:150,000.

Your rendered image should be similar to the following:

10. Toggle the top mosaic (Nominal) layer on and off by selecting and clearing the

SPOT4_Nominal_Mosaic layer check box in the ArcMap Table Of Contents.


30

11. Compare how well the ROADSEG layer agrees with the corresponding road

features in the image.

The purpose of this comparison is to demonstrate the improved positional accuracy of image features relative to a geocoded reference layer (true position) when GCPs are used to refine the math model.

Begin by analyzing the accuracy of the nominal mosaic relative to the geocoded vector layer. Notice that there is a large displacement between the positions of the roads in the image relative to the position of the corresponding vector layer. Next, compare this image with the refined mosaic. Notice that the road vector layer almost perfectly overlays the corresponding road segments in the image. This example demonstrates that it is possible to achieve significant improvements in accuracy when GCPs are used to refine the math model.

Documents

GIToolsV2_tutorial.pdf