2009/10/3 Adam Ratcliffe <[email protected]>: > Hi, > > 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 >
As already said, this is effect of not filled holes. There is no other way than to use hole-filling software (search google for srtm and filling etc). I don't remember what I used, it was probably some window dialog clicking shareware, but gdal has some python script for that (I didn't tried it). In my case mountains in the middle had similar artefacts like Yours (from right part of relief-artifacts.png) and now look like that: http://mapa.ump.waw.pl/ump-www/?zoom=12&lat=49.18671&lon=20.21316&layers=B00000FT However, I doubt big holes on left part of Your image could be filled nicely with anything other then different elevation source. > Being a little bit new to this I'm neither sure of why the artifacts exist > 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 gdalwarp > call - I observed no difference with these options. I also tried setting the > error threshold '-et' option to 0 which had no effect. > > Any suggestions on how to tackle this problem are much appreciated. > In this thread You can find my earlier notes concerning hill shading in mapnik: http://www.nabble.com/My-patches-for-hill-shading-td22215531.html I also based on mentioned Wiki(HikingBikingMaps), but made some adjustment to improve quality and effect to my needs (interpolation, fine alignment, composing methods), almost all patches are in recent versions of Mapnik. Just one note, I use a little modified mapnik and composite method: grain_merge181, that compared to grain_merge has moved middle point (value of no shading effect) from 128 to 181 to have bigger range of shadows then highlights. -- Marcin Rudowski _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
