>>> >>> I just noticed a strange behaviour when trying to render 8-Bit PNGs: >>> Mapnik seems to stop drawing features when it runs out of colors (or at >>> least that is my interpretation so far). > > In the end it turned out that it this probably wasn't related to PNG > rendering at all but to some rather strange multithreading/IO issues > when generating tiles from shapefiles on my machine.
Yep, it looks like during rendering the map extent was changed. This indicates that the same map was likely being shared between two different threads. This should not be happening with generate_tiles.py. Were you maybe using TileCache or TileStache? Both of these applications cache a single map instance so they need to be deployed within apache in multiprocess mode. Let me know if you need more details on this. > > I haven't fully investigated the issue yet but I am quite sure it > doesn't have to do with PNG output after all. > > Best, > > Flo > > >> >> OK I just found the documentation on >> >> http://trac.mapnik.org/wiki/OutputFormats >> >> I did Google around yesterday but somehow didn't find this. Sorry for >> the noise. >> >> Flo >> >> >>> >>> It's best illustrated with the attached tiles - the first was saved as >>> 24-Bit PNG, the other one as 8-Bit using >>> >>> mapnik.Image.save(uri, 'png256') >>> >>> (in the context of OSM's generate_tiles.py) >>> >>> I would have expected the latter to be dithered or otherwise distorted, >>> but I cannot explain to myself why parts of distinctive layers (roads >>> and rivers in the upper part of the image) are omitted, especially given >>> that the colors used there are present in the rest of the image. >>> >>> Can anyone explain to me what is going on here? Or even better give some >>> hints or pointers to code how this could be fixed/avoided. >>> >>> Best, >>> >>> Flo >>> >> >> _______________________________________________ >> Mapnik-users mailing list >> [email protected] >> https://lists.berlios.de/mailman/listinfo/mapnik-users > _______________________________________________ > Mapnik-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/mapnik-users _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
