Hi Peter, I would suggest looking at the ENVI task for RPC orthorectification: http://www.exelisvis.com/...ctificationTask.html That link provides an example of how to use IDL to run the RPCOrthorectification task. This template can be extending to use multiple images with a for loop where the ImageFile, DEMFile, and GCPFile are defined in a list or just once if all your images use the same DEM and GCP. To make things easier than typing a list of 200 names of files, you can try to use FILE_SEARCH if all your files have the same file extension (http://www.exelisvis.com/...s/FILE_SEARCH.html).