jonas nielsen <jonasln <at> gmail.com> writes: > > > The original images that the overviews are built on are 10000 by 10000 pixels. > > And yes, the artifacts appear without reprojection. > > -Jonas
Hi, I do also see such artifacts with Mapserver tileindex layers when zoomed far away so that the overviews are used. I have a slight feeling that it may come from subsampling when the resolution and image extents do not math exactly. With your images I would guess that the first overview levels up to 16 might work fine because the image extents can be filled exactly with the new subsampled pixels. samling theoretical level image width 1 10000 2 5000 4 2500 8 1250 16 625 32 312.5 64 156.25 128 78.125 256 39.0625 512 19.53125 1024 9.765625 2048 4.8828125 I cannot imagine what GDAL is really doing at, let's say, redused level 128. Your whole image width could be covered with 78.125 pixels, each 12.8 meters wide. Obviously this is not possible. Either the pixel size must be a bit smaller or this overview level contains 79 pixels and thus it is a bit wider than the original image. If the latter is the case, what colour does the border pixels, which have the majority of their area off-site, get? I may be totally on the wrong track but this is what I have been wondering. Same looking but warp process related artifacts can be seen in figure 3 in article http://www.scangis.org/scangis2007/papers/r3_rahkonen.pdf. Figures 4 and 5 show how we managed to remove them. -Jukka Rahkonen- _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
