I don't believe SPOT comes with a separate RPC file. RPCs for SPOT are generated from the metadata in the DIM. EX does not directly support SPOT in DIMAP format but instead just opens the TIFF. So you would need to open the SPOT file in ENVI as DIMAP, turn on RPC emulation by editing the Header, and save it out as an ENVI format file. This should write the RPCs into the ENVI header which then could be input to the RPC orthorectification. Of course, if you have ENVI, you could do all of this within ENVI. I don't think EX can read any ALOS data and very few PRISM products come with RPCs. I don't think the format of the DEM matters as long as it is in a supported image format and the DEM can have a larger pixel size than the image.

Hi I highly appreciate your valuable response. Thank you very much. I have only ENVI EX to process data. I just found that ENVI EX support DIMAP, therefore I think that it can read directly SPOT image. Because you mentioned that RPC file is located in the metadata of DIM (I think it is XML file), do you think that the RPC Orthorectification od ENVI EX will automatically find the RPC file and run properly?

Ah, you are correct. The help states SPOT DIMAP is supported but EX does not appear to extract the metadata to generate the RPCs. It is not listed as a supported data type for RPC ortho in EX.

Hi, Thank you very much for your response. In conclusion, I can not use both ALOS and SPOT for the rpc orthorectification in ENVI EX right? Actually, I can not see SPOT DIMAP as supproted data type for RPC ortho in EX. How is about IKONOS, which is the supported data type for RPC Ortho in ENVI EX. do you have experience in using IKONOS? Does ENVI EX can read RPC in the metadata file of this data and process RPC Orthorectification for this data?

The ENVI EX documentation, under Using Workflows > About the RPC Orthorectification Workflow, says that IKONOS are supported. Here's the whole text from that Help section, since you seem to not have access to that documentation: The RPC Orthorectification workflow performs orthorectification of a single-scene image using the rational polynomial coefficients (RPC) model. Orthorectification geometrically corrects the data to remove distortions that occur during image capture. ENVI EX supports data from the following sensors: GeoEye-1 IKONOS OrbView-3 QuickBird WorldView-1 Data from each of these sensors typically include an ancillary RPC file. ENVI EX also supports the ENVI format with RPC INFO defined in the header and the NITF format with RPC information in the metadata. If you have both standard map information and RPC INFO in the header, you need to remove the standard map information in the ENVI header to continue. The following are required input for RPC orthorectification: The image to rectify RPC model Elevation information I hope that clarifies things for you. - Peg