[mkgmap-dev] Trouble getting some multipolygons to render inmkgmap

Sun Sep 26 20:26:43 BST 2010

WanMil schrieb am 24.09.2010 19:29:
>> My understanding of the multipolygons is, that the tags may EITHER be
>> in the
>> relation OR on the outer polygons. So the outerpoylgons are only to be
>> used,
>> when there are no tags on the relation.
>> If the relation itself is tagged and there is a tag on the
>> outerpolygons, this
>> does logical mean, that the outerpolygon tags apply to the complete area
>> including the inner-area.
> 
> You càn check yourself if it's now the time to remove this polygon list.
> I have attached a patch that follows your proposal. Just test it and let
> us know.

I tried your patch today, and I think it looks quite promising. Implementing
such a strict scheme will certainly show some faulty multipolygon (e.g.
Aussenalster in Hamburg), but perhaps this will encourage a cleaner tagging of
such relations.

I think the patch has still one problem: If the tags of the outerpolygon are not
used for the multipolygon area, they must still be used as a stand-alone polygon.

As an example take a nature reserve consisting of a wood with a lake inside.
This migth be mapped with two polygons and a relation:
polygon A: leisure=nature_reserve (the complete area)
polygon B: natural=water (only the inner area)
multipolygon relation: natural=wood and outer=polygon A and inner=polygon B
(only the surrounding area)

Right now polygon A seems to be missing in the resulting map.

Gruss
Torsten