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

Mon Sep 27 14:20:12 BST 2010

Torsten Leistikow (de_muur at gmx.de) wrote:

> 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.
>
But how would mkgmap know which of the two outer polygon types to use  
(ie nature reserve or wood)?

-- 
Charlie