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

Sat Oct 16 11:35:52 BST 2010

Am 13.10.2010 22:09, schrieb WanMil:
>> charlie at cferrero.net schrieb am 27.09.2010 15:20:
>>>> 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)?
>>
>> It should use both:
>>
>> The nature reserve should cover the complete area.
>>
>> The wood should cover only the area defined by the multipolygon.
>>
>> This is (one of) the intended tagging of the multipolygons. Allowed alternatives
>> (with the same logical interpretation) would be:
>>
>> 1. You could use an additional polygon for the outer limit of the multipolygon
>> (polygon C) which would have the same nodes as polygon A. Polygon A and B would
>> stay unchanged.
>> multipolygon relation: natural=wood and outer=polygon C and inner=polygon B
>>
>> 2. You could put all tags from the relation on polygon C, polygon A and B would
>> stay unchanged.
>> polygon B: natural=wood
>> multipolygon relation: outer=polygon A and inner=polygon B
>>
>> 3. You could move the nature reserve tag into the multipolygon area and the
>> inner area.
>> polygon A:
>> polygon B: natural=water and leisure=nature_reserve
>> multipolygon relation: natural=wood and leisure=nature_reserve and outer=polygon
>> A and inner=polygon B
>>
>> 4. And you could move the tags from the relation of variant 3 to the outer polygon.
>> polygon A: natural=wood and leisure=nature_reserve
>> polygon B: natural=water and leisure=nature_reserve
>> multipolygon relation: outer=polygon A and inner=polygon B
>>
>> I think these five possibilities are all allowed under the actual accepted
>> multipolygon scheme and they should all result in nearly the same garmin map.
>> (Alternative 3 and 4 split the nature reserve into to areas, but in the end it
>> covers teh same area).
>>
>> Gruss
>> Torsten
>
> Hi Torsten,
>
> I am back and I have thought about your request. It would be possible to
> implement a patch which keeps the original polygons in case they are
> tagged differently to the multipolygon.
>
> I have also read Charlies answers and before digging in the code I would
> know if this feature is really needed and useful? Can you estimate how
> many multipolygons are affected?
>
> WanMil

Hi,

I have posted a patch (Improved tagging of multipolygons) that should 
fix it. Please test it!

WanMil