I was creating DEM and got Warning Message: TRIANGULATE: Not enough valid and unique points specified. Please consult the supplier of the application. I am using 3N and 3B from ASTER Image. Used GCP from Topo maps, lat/long and elevation information, but at last moment I get the message. Tried with collecting just 3-5 GCP's as well as more. If anyone has suggestion on this problem or more detailed tutorial, please let me know. Thanks Kabindra