[mkgmap-dev] problems with rendering of long riverbank (multipolygons)

Thu May 19 17:55:35 BST 2011

> Recently someone noticed flooding on the openmtbmap in Belgium south of Maastricht:
> http://forum.gps.nl/viewtopic.php?f=109&t=34597&p=277200#p277200
>
> I have noticed related issues with floodings west of Maastricht on Lambertus' maps and on my own Openfietsmap parts of the same Albertcanal are "dry". Main cause seems a very long multipolygon relation of the Albertcanal: http://www.openstreetmap.org/browse/relation/1424029
>
> On places where the tile borders are crossing this multipolygon mkgmap has problems with rendering (because the ends of the multipolgygon are way outside the tiles). Splitting up the multipolygon in smaller parts in osm seems not the way to solve these rendering problems because I think it's a bug in mkgmap that should be solved here instead of on osm. Any ideas?
>

If you assume that the multipolygon algorithm has a problem you should 
change the log level of the Multipolygon class:
uk.me.parabola.mkgmap.reader.osm.MultiPolygonRelation.level=FINE

Enabling the logging is described at 
http://wiki.openstreetmap.org/wiki/Mkgmap/dev#Enabling_Debugging

You can search the logfiles for the relation id and check what the 
multipolygon code is doing. The logfiles get big so it might be good to 
compile the relevant tiles only.

If you have questions just send the logfile.

WanMil