[mkgmap-dev] [mp: PATCH] Multipolygon handling - decomposed polygons

Sat Jan 9 13:09:36 GMT 2010

>
>
> Ralf Kleineisel schrieb:
>> On 01/09/2010 10:08 AM, WanMil wrote:
>>
>>
>>> Another idea is to add some specific tags by the mulitpolygon algorithm
>>> that link to the other pieces of the formerly big forrest. This could be
>>> evaluated by the SizeFilter?
>>>
>>
>> Another idea (don't know if this is possible):
>>
>> You have a big multipolygon forest. You could duplicate it. One copy
>> without small inner polygons for the low resolutions. Another copy with
>> the inner polygons which gets splitted for the higher resolutions. The
>> copies could be marked with some mkgmap internal tag and used later.
>>
>>
> May I propose to move the whole multipolygon handling to the filter chain?
> Then there is _no need_ for additional tags and duplicated polygons and
> possible remerging of them. The filter chain is run for each resolution
> level. With each run the poylgons could be handled accordingly.
>
> I don't think, your ideas are wrong. I appreciate your work. But I think
> its made more complicated than actually needed.
>

Interesting idea!

I am not very deep in the filter things, so please let me know if I am 
on the complete wrong way.
Some thoughts about moving mulitpolygon handling to the filter chain:

* Computation time for multipolygon handling will be multiplied by the 
number of resolutions. Probably this is ok as the current implementation 
seems to be quite quick.

* At which point should the multipolygon filter run? This might be a 
problem.
Example:
1st - before the SizeFilter: As before the mp code splits large polygons 
to smaller pieces that might be removed by size filter (or the dp filter?)
2nd - after the SizeFilter: The size filter removes small lines(?) and 
polygons that otherwise would be composed to larger polygons by the mp code.

Mmh, 1st solution seems to be ok. In low resolutions mp code only cuts 
out large inner holes. In this case it shouldn't matter if some small 
pieces are cut from the large outer polygon.

WanMil