Hi Adam, > I've been generating hillshade images using the SRTM3 data, these are > looking good but I've noticed some artifacts around the area of the > Southern Alps of New Zealand. These can be seen in this sample image: > http://test.geosmart.co.nz/images/relief-artifacts.png
I noticed some improvements when leaving out the -dstnodata option, but of course there are still artefacts left (only some hole-filling could remove that, more or less plausibly, and I do not know of any automatic way to achieve that). So for small artefacts, this seems to work rather well, while for larger ones, they seem to be still pretty well visible. In the Alps (New Zealand or Europe ...) there will probably still be another issue making this worse: I experimented with leaving out the mentioned option for generating hill shadings and reliefs; when looking at the generated reliefs, it seems like now the missing parts are filled with the color for the lowest configured elevation (for me eg. dark green instead of black); this is an improvement (in my eyes), but if dark green spots appear in the grey or white of high mountains, then that of course still is pretty striking. As said, I think the only way around that is using filling for voids, or using preprocessed data, eg. CIAT/CSI/CGIAR, mentioned on the HikingBikingMaps wiki page. These currently have licensing issues because they are non-commercial only; but with the possible move to ODbL in the future, and the possibility to license products other than CC-BY-SA (in my understanding) this can be resolved, if non-commercial use is sufficient for you (otherwise you might have to negotiate for other licenses or datasets). > and how to remove them in the processing of the data. So far I've > experimented with some of the options to gdalwarp, on the Hiking/Biking > maps wiki page it was suggested to pass "-wt Float32 -ot Float32" to the These I introduced, because I was generating maps for rather small areas with a high level of details. When doing interpolation of DEM data for these, I noticed steps instead of smooth elevation transitions, which arose because of the limited elevation resolution of the default int values. For large areas, you might want to leave them out as any effects will probably not be noticeable, and the size of the files is multiplied, such that any memory limits will be hit earlier that without the floats. Yours, Holger _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
