Hi, Gerd, your additional interpolation would be redundant. Side note: comparison of double and integer doesn't look safe. Maybe would be better if interpolateHeight() returned integer? Frank, I understand your idea, but please note, that your choice of triangle is arbitrary. There are 2 ways of dividing a square and if you would choose the other way, results would be different and not only for the middle point. This suggest that the solution isn't complete. Classic bilinear interpolation seems better, but differences are small and actual map looks more or less the same. I have attached second patch, which apply interpolation when only 2 values on any edge are present. Another topic. I observe some DEM artifacts, when displaying area near the border of dem-poly. There are small rectangles without shading within a bigger tile. They appear at random, when scrolling or zooming map in BaseCamp or Mapsource. Ctrl-G doesn't help. See attached img. I haven't noticed the problem, when compiling a map without dem-poly. Maybe it is a result of slanted edge of DEM clipped by poly. -- Best regards, Andrzej
