On 11/10/2012 11:45, Felix Hartmann wrote:
I think even if you define the order, it won't really workout well. Also you would need to check if all devices have the same order. At least on the consumer GPS side, Garmin turned the draw order upside down in newer vs older generation gps devices (same holds true for old Mapsource 6.13 vs Basecamp >=v3).
Maybe there would be a need for proper overlay checking with blacklists which types may not be in the same area as others, and then mkgmap cutting out some polygons. Or mkgmap cutting out smaller polygons from larger ones, similar to how mapnik does it... I cannot imagine this to be easy though (because I cannot even come up with a clean concept on how this should be done).
RheinSkipper & I ran a small test with a number of overlapping polygons & made OSM files with these objects in different orders. The OSM file with the top polygons listed last worked correctly, implying that the device being used rendered these objects in first-to-last order. If a user's device rendered in reverse order, then that user could simply specify their layer parameters with values high-to-low rather than low-to-high. Our suggested method ought to cause the least implementation work, as it would not require any low-level hacking of mkgmap.