[mkgmap-dev] Bogus warnings about intersected ways in multipolygons

Mon Jan 25 21:39:56 GMT 2010

I don't think these warnings are bogus. Mkgmap definitely has problems
with multipolygons. The Languedoc-Roussillon extract (southern France)
from Geofabrik provokes about a hundred of these warnings. But I believe
that the intersected ways are being generated by mkgmap and that the OSM
data is OK. Mkgmap-r1475 did not have this problem but r1502 and r1507
both do. I am unable to pinpoint more accurately when the behaviour
changed because I do not have copies of the relevant releases. Perhaps
r1494 could be put back on the web site, in the hope that we might have
the benefit of the fixes to generate-sea without the multipolygon
problems.

Exactly where the problems show up can depend on where the tiles are
split. One example is at
http://www.openstreetmap.org/?lat=43.4047&lon=3.5107&zoom=13&layers=
B000FTF
as seen on Lambertus' site. Take a look at his tile 63240406.img dated
20-01-2010. If you look at the vineyards (land-use polygons) in the
vicinity of Pinet, you will see an obvious straight edge which is
spurious, and areas where the inside and outside of the polygon have
swapped over.