Use Build RPCs to compute rational polynomial coefficient (RPC) information for the following:
- Scanned aerial photographs from a frame camera.
- Digital aerial photographs with a frame central projection (including Vexcel UltraCamD).
- Digital aerial photographs with a line central projection (including Leica ADS40/ADS80 and STARLABO TLS).
- Imagery from any generic pushbroom sensor (including ALOS PRISM and AVINIR, ASTER, Cartosat-1, FORMOSAT-2, GeoEye-1, IKONOS, IRS-C, KOMPSAT-2, MOMS, QuickBird, RapidEye, WorldView-1 and -2, and SPOT) as long as GCPs are available.
Note: ENVI automatically computes RPC map information for Leica ADS40/ADS80 files if the necessary ancillary files are present. ASTER, SPOT, and FORMOSAT-2 data files contain RPC information, which you can retain before orthorectification or DEM extraction and avoid using Build RPCs altogether.
RPCs are computed using a digital photogrammetry technique that uses a collinearity equation to construct sensor geometry, where the object point, perspective center, and image point are all on the same space line. The technique involves a series of transformations involving pixel, camera, image-space, and ground coordinate systems.
For single-image orthorectification, the technique includes two preprocessing steps to build the sensor geometry: interior orientation (which transforms the pixel coordinate system to the camera coordinate system), and exterior orientation (which determines the position and angular orientation parameters associated with the image). See Frame and Line Central Projections Background for more information.
Once RPCs are computed, the RPC information is added to the input file header so that you can use the file with DEM Extraction.
See the following sections to begin: