In step 2 of 9 of the DEM Extraction Wizard, you select the source of your stereo GCPs. This is an optional step, since the default selection is No GCPs (relative DEM values only). You can either accept the default and click Next to move on to Step 4 of the Wizard, or you can select one of two other choices as the source of your GCPs.

  1. Choose the source of the stereo GCPs by selecting one of the following choices (for information on relative and absolute DEMs, see Output DEM Types):
    • No GCPs (relative DEM values only): This is the default selection. You can elect to not use GCPs, in which case Step 3 of 9 (GCP Collection) is skipped. Choosing this option would result in a relative DEM.
    • Define GCPs Interactively: This option requires that you manually enter, load, and edit GCPs that will tie the DEM to a planar map projection, therefore resulting in an absolute DEM.
    • Read GCPs From File: This option requires that you select a GCP file from which to read GCPs. You must provide a filename in the User Defined GCP File field.
  2. To load a pre-existing GCP file, click Select New GCP File. The Select Input GCP File dialog appears. Navigate to your GCP file and click Open to load it into the Wizard.
  3. The Examine and Edit Stereo GCPs option is only available if you have loaded a GCP file into the Wizard. Selecting No (default) results in skipping Step 3 of 9 (GCP Collection).

    4. Note: If you are reading GCPs from a file, you should click the Examine and Edit Stereo GCPs toggle button to select Yes, so you may view and edit the GCPs.

  4. Click Next to continue to the next step of the wizard.