Change Detection for Optical Functions

Transcription

1 Change Detection for Optical Functions Geomatica 2012 introduced new algorithms to facilitate Change Detection for Optical Functions. New algorithms include CHDETOP and EXPLORAS. The purpose of this tutorial is to provide you with a friendly and easy to follow step-bystep guide for using the new Change Detection algorithms for Optical Functions in PCI Geomatica 2013 using the CHDETOP and EXPOLRAS algorithms. CHDETOP - Detects differences between two input raster images ("new" and "reference"). Typically, the function is used on a pair of images from the same optical satellite sensor and, depending on the sensor; tasseled caps can be used to determine the changes. EXPOLRAS - Converts an input raster image to a binary image using a specified threshold value, then extracts polygons from the resulting binary image and filters them based on area and compactness values. The data for this tutorial can be found at the link below: ftp://ftp.pcigeomatics.com/pub/support/data/changedet.zip GEOMATICA FOCUS 1. Open Geomatica Application Bar Note: Focus will automatically open at the same time as the Geomatica Application bar Page 1

2 2. Navigate to the directory where you extracted the ChangeDet.zip content to. 3. Drag and drop the Level1_OptChgDet.gpr file into the Focus window. 4. A project opens that contains 4 map layers, but only the bottom layer is toggled on. Description: This is a Landsat-5 TM image captured in 1990 of the Prince George area in Northern British Columbia, Canada. This area is well known for the logging activities that occur here. This particular image is used as a reference (before) image in order to perform our change detection, which looks to quickly and easily identify vegetation loss (deforestation). 5. Toggle the third layer on. Page 2

3 Description: This is a Landsat-7 ETM+ image captured in 1999 of the same area as described above. This image is used as the input (after) image in which change detection is performed for. Specifically, this demo highlights and extracts areas in the 1999 image where vegetation has been removed. 6. Toggle the top (first) layer and the third layer on and off in sequence. The polygons created accurately highlight and identify where vegetation has been removed. 7. Toggle the 1 st and 3 rd layer on and off to show how well you were able to highlight and extract polygons of the areas where vegetation has been removed. GENERATING AN AREA REPORT 1. Open Algorithm Librarian In the Focus menu bar, click on Tools Algorithm Librarian 2. In the Algorithm Librarian window, click Find 3. Check the Match algorithm description using all Keywords 4. Uncheck the Match algorithm name 5. In the Find what text box, type Area Report Page 3

4 6. Click Find Next 7. AREAREPORT module is automatically selected. Click Open or double click on the module 8. In the Files tab, expand the Files tree branch and select the raster channel named Area 9. Click on the Input Params1 tab, and change Reporting Units to any unit that makes the most sense for your area (i.e. Square Kilometres) 10. Click Run Page 4

5 11. After the progress bar disappears, click on the Log tab Description: The log above shows the total area that has been deforested (left red box) as well as a relative measure (Right red box). INITIAL CHANGE DETECTION 1. Return to your Focus window with the Level2_OptChgDet.gpr project loaded 2. In the Focus menu bar, click on Tools Algorithm Librarian 3. In the Algorithm Librarian window, click Find 4. Check the Match algorithm description using all Keywords 5. Uncheck the Match algorithm name 6. In the Find what text box, type Optical Change 7. Click Find Next 8. The CHDETOP module is automatically selected Page 5

6 9. Double click on the module or click Open 10. The CHDETOP panel opens with the Files tab active 11. Expand the InputNew tree branch 12. Select all 6 channels from the 1999 image 13. Retract the InputNew branch and expand the InputRef branch 14. Select all 6 channels from the 1990 image 15. Retract the InputRef branch 16. In the Output Ports section (bottom of File tab) 17. Uncheck the Viewer-Grayscale Page 6

7 18. Check C:\PCI Geomatics\...\Untitled.pix 19. Click the Browse button for Output Ports 20. In File Selector, navigate to C:\...\ChangeDet\change 21. Name the file as opticalchange_demo.pix 22. Click Save 23. Click on the Input Params 1 tab 24. Change the Change detection algorithm to Intensity Ratio 25. Click Run 26. Once the Algorithm has finished running, close the module and minimize Algorithm Librarian Note: The output file is automatically added to the project 27. In Focus, click on the Files tab 28. Expand the branch for the top file (opticalchange_demo.pix) Description: The output change detection file contains 4 channels. The first channel is a SPANS (averaged image of the input 6 bands from the 1999 image). The second channel is a SPANS (averaged image of the reference 6 bands from the 1990 image). The third channel is the absolute values of change, as per the intensity ratio algorithm. Page 7

8 The fourth channel is a raster that ranks change based on percentiles (relative change). We will be using the fourth channel for identifying and extracting polygons of deforestation. 29. Right click on the fourth channel (Ranked Changes in Percentiles) and select View As Pseudocolor 30. The change image loads into Focus 31. Toggle this layer and the 1999 image layer on and off to show that deforestation change is generally provided the following colors: Bright red, purple and white. Page 8

9 EXTRACT CHANGE AS POLYGONS 1. Restore the Algorithm Librarian window 2. Click Find 3. Change Find what to Extract polygon 4. The EXPOLRAS algorithm is selected, double click on it or click Open 5. The EXPOLRAS algorithm module opens 6. In the Files tab, click Channel 4 (Ranked Changes in Percentiles) from the opticalchange_demo.pix file 7. Click Input Params 1 tab 8. Set the Threshold minimum value to Set the Minimum area (pixels) to Leave all other values as default Page 9

10 11. Click Run Description: Once the process has completed, the polygons will automatically be rendered in the viewer 12. Close The EXPOLRAS module and Algorithm Librarian 13. In Focus, zoom to 1:1 14. Toggle the Ranked Change layer off 15. Demonstrate how the polygons do a very nice job of outlining the areas where deforestation has occurred. This can be accomplished by toggling the 1999 image on and off Note: The area report or the change detection and extract polygon algorithms can be created for identifying and extracting other forms of change (i.e. new vegetation). Page 10