After you pre-process certain data files and choose to perform orthorectification, ENVI’s orthorectification tools may prompt you for an associated RPC file because the necessary tags from the original file are no longer present or associated with the processed files. In the case of ASTER, SPOT, or FORMOSAT-2 data, ENVI calculates the RPCs from information in the original files, so there is no external source for the RPCs and you cannot perform orthorectification.

You can retain RPC information from ASTER, SPOT, and FORMOSAT-2 data files by storing the information in an ENVI header file prior to processing the data. Perform the following steps:

  1. Open the ASTER, SPOT, or FORMOSAT-2 file.
  2. From the Toolbox, select Raster Management > Edit ENVI Header. The File Selection dialog appears.
  3. Select the data file, and click OK.
  4. In the Edit Raster Metadata dialog, scroll to the RPC or RSM Projection Emulation section.
  5. Click the RPC Projection Emulation Enabled toggle button to select On.
  6. Click OK in the RPC Parameters dialog, then again in the Edit Raster Metadata dialog to retain the new header settings.

These steps prompt ENVI to calculate the RPCs and write them to an ENVI header file (.hdr) in the same directory as the data file. Now you can process the data. The RPCs in the header file are passed to the processed file so that you can perform orthorectification.