You should rasterize the polygonmap (for example studyarea.mpa -> studyarea.mpr) Then a IFF statement can do the job of masking away the area in the aerial photo (photo.mpr) outside this studyarea.
Output = IFF(studyarea,photo,"?") if the output is of domain Class or Id Output = IFF(studyarea,photo,?) if the output is a value domain The 1st argument in the IFF function is a boolean that is true or false for pixels inside or outside the study area respectively. In case if "true" the photo pixelvalue is taken, otherwise the map pixel becomes ? (undefined). See also the ILWIS online Help or the User's Guide on UNDEFINED values in MapCalculations -----Original Message----- From: osame alkaaby [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 12, 2003 09:12 To: Ilwis list Subject: (ilwis-list) Study area Dear all: I have a polygin that indicate the border of sudy area( it's not a regular shape).How can I overlay this polygon on image(TM data or arial photo)and then extract just the area which located inside the polygon. Alkaaby ________________________________________________________ To leave the ILWIS-LIST discussion list, send a email with 'unsubscribe ilwis-list' in the body to '[EMAIL PROTECTED]'
