[mkgmap-dev] Incorrect multipolygon warnings?

Sun Mar 28 13:39:57 BST 2010

> Hi,
>
> Whilst processing Italy, I've been getting a lot of mp warnings like:
> 2010/03/27 13:57:27 WARNING (MultiPolygonRelation): 63242013.osm.gz:
> Polygon 4611686018427439638 intersects itself. It is splitted into 2
> polygons.
> 2010/03/27 13:57:27 WARNING (MultiPolygonRelation): 63242013.osm.gz: The
> polygon is composed of
> 2010/03/27 13:57:27 WARNING (MultiPolygonRelation): 63242013.osm.gz: -
> http://www.openstreetmap.org/browse/way/36433060
>
> I can't see anything wrong with this mp and the JOSM validator does not
> pick up on anything.  Is this an error with mkgmap's MP code or am I
> missing something?

Yes and no. While reading in the data from osm files mkgmap converts all 
coordinates to the garmin internal format. This reduces the resolution 
of the coordinates. So the multipolygon code works with other 
coordinates than OSM. Due to this a polygon might intersect itself 
although it does not in the original OSM data.

>
> Here's another:
> 2010/03/27 13:57:27 WARNING (MultiPolygonRelation): 63242013.osm.gz:
> Polygon 4611686018427439886 intersects itself. It is splitted into 2
> polygons.
> 2010/03/27 13:57:27 WARNING (MultiPolygonRelation): 63242013.osm.gz: The
> polygon is composed of
> 2010/03/27 13:57:27 WARNING (MultiPolygonRelation): 63242013.osm.gz: -
> http://www.openstreetmap.org/browse/way/36434237
>