Hi Frank, I checked the vertices and the problem is exactly as you guessed, raster and polygon are matching at the vertices. I will try to add more vertices to the polygon layer to solve the problem, thank you very much! By the way, this problem should always be the case if projections of map and data are different from each other, isn't it? Normally I would expect that on-the-fly projection algorithms be handling such cases, but as far as I can see this is not the case. I tried ArcView and it has the same problem too.
Best regards, --- Serkan Girgin [EMAIL PROTECTED] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Frank Warmerdam Sent: Friday, December 16, 2005 4:31 AM To: Serkan Girgin Cc: [email protected] Subject: Re: [UMN_MAPSERVER-USERS] projection problem On 12/15/05, Serkan Girgin <[EMAIL PROTECTED]> wrote: > Hi! > > I have a problem with on-the-fly projection and I would be grateful if you > can help me. In my mapfile there is a raster Landsat image in UTM projection > (zone 37N) and a shapefile containing a polygon with the same extent of the > raster, again in UTM projection. When I set the overall projection of the > mapfile to UTM these two layers coincide perfectly as expected (see > landsat_utm.jpg). But when I change mapfile projection to a different > projection, e.g. geographic or Lambert Conformal Conic, a shift occurs > between the layers and they do not coincide (see landsat_lcc.jpg). Do you > have any idea why this happens? You can find mapfiles that I used below. Serkan, I'm not sure from this information, but I would guess that you get different results because the polygon is only reprojected at the vertices and then the new polygon is drawn "straight" between these transformed points. While the raster is reprojected for each pixel. If the polygon is big enough, this could account for the displacement. But if this is the case, you should see the polygon match up closely with the raster as you near one of the vertices of the polygon. Best regards, -- ---------------------------------------+------------------------------------ -- I set the clouds in motion - turn up | Frank Warmerdam, [EMAIL PROTECTED] light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent
