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Select Stereo Tie Points

Select Stereo Tie Points

Collecting tie points is an essential step in the DEM extraction process. The DEM Extraction Module provides a standalone tool that enables you to collect stereo tie points and save the results to an ASCII file.

  1. From the Toolbox, select Terrain > DEM Extraction > Select Stereo Tie Points. The Select Left Stereo Pair Image dialog opens.
  2. When you click OK in the Select Right Stereo Pair Image dialog, the RPCs are computed and the left and right stereo images open in new display groups. The Stereo Pair Tie Points for DEM Extraction dialog opens.
  3. Select tie points. See Viewing, Adding, Editing Tie Points for detailed information about this dialog and methods for generating, viewing, and editing tie points.
  4. Click Generate Tie Points Automatically, to have the tie points chosen for you. The Generate Tie Points Automatically dialog opens.
  5. Click OK to start the Automatic Tie Point Generation process. When the processing is done, the tie points are shown in the images, and the Stereo Pair Tie Points for DEM Extraction dialog looks similar to the following figure.
  6. If the Maximum Y Parallax value is greater than 10, you must edit the tie points.
  7. In the Stereo Pair Tie Points for DEM Extraction dialog, click OK when you are finished editing the tie points. An ENVI query dialog opens asking if you want to save the stereo tie points to an ASCII file.
    • Click Cancel to return to the Stereo Pair Tie Points for DEM Extraction dialog.
    • Click No to exit the Stereo Pair Tie Points for DEM Extraction dialog without saving the selected tie points.
    • Click Yes to save the stereo tie points to an ASCII file. The Save Stereo Pair Tie Points to ASCII dialog opens.
  8. In the Save Stereo Pair Tie Points to ASCII dialog, type the filename for the output file, or click Choose to navigate to the desired directory and filename.
  9. Click OK. The Stereo Pair Tie Points for DEM Extraction dialog closes, as do the stereo image display groups.



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