There is a lot of ENVI functionality that is not revealed to the public at large in order to maintain market value for the ENVI product. I can certainly share with you this much: '.envi' files tend to be flat binary data files, the structure of which is all described in a file of matching name with the '.hdr' extension. The '.hdr' is an ASCII text file and you will find many of the field descriptions in such a file to be completely intuititive, e.g. "bands", "samples", "lines", "data type". From this, you can usually figure out what pixel grid to create in IDL that can hold a READU import of the contents of the '.envi' file. After that, though, knowing how to visualize the data that you import into the pixel grid can be, for some data sets, very complicated. For complicated visualizations ENVI does not reveal its algorithms as open source code; they are based on years of costly evolutionary development. Consequently, if you are wanting to share visualizations with customers who do not have ENVI licenses, then we recommend that you make the complete visualizations in your own ENVI sessions, and save snapshots of the final visualization in well-known image file formats that IDL includes easy readers for, like PNG, TIFF or JPEG2000. (Note that I do not recommend saving visualizations in the lossy JPEG format.) I do not have an answher about your ROI and DEM question; perhaps some other Forum reader can answer that? James Jones IDL Technical Support