> On Nov 29, 2009, at 9:22 PM, Hemant Bist <[email protected]> wrote: > >> Hi, >> Mapnik is correctly generating the tiles for me. >> I am trying to figure out if Mapnik can tell me if the tile (or map >> I generated) is empty(i.e. there is no information in the tile).
Mapnik does not have any way to report empty tiles. I think this is easiest just in python. In fact generate_tiles.py already does this when it prints "Empty Tile", see line 109-110: http://trac.openstreetmap.org/browser/applications/rendering/mapnik/generate_tiles.py#L107 >> I have a sparse map with few polygons covering less than 50% of the >> total map rendered. >> >> The empty tiles have small size so that would be one heuristic. I >> am hoping there is some better way: Right, size/bytes/len is not exact because it will be dependent on the image encoding and tile size, which you might change, but I don't have any other ideas atm. >> either Mapnik can tell me or may >> there is some imagemagick or some other tool that can check that all >> the pixels in the png are transparent(I am using transparent >> background). Despite the above mentioned limitation, calling len() is another option. Maybe around line 89 (http://trac.openstreetmap.org/browser/applications/rendering/mapnik/generate_tiles.py#L89 ) you could do: if len(im) == 116: ...then don't save tile.... As a quick check indicates that a 256x256 transparent tile (confirm for your system/build) is 116 when png256: >>> import mapnik >>> im = mapnik.Image(256,256) >>> im.background = mapnik.Color('transparent') >>> len(im.tostring('png256')) 116 Note: not tested... >> >> I am currently using generate_tiles.py. >> >> Would appreciate any pointers. In past I have benefited from >> suggestion for workarounds on this list, even if there is no direct >> solution. >> >> Happy Holidays! >> HB > _______________________________________________ > 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
