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

Sun Jan 10 17:58:00 GMT 2010

>   
>> But I see a technical problem arise:
>> In the filter chain there aren't any more tags or other information on
>> how polygons are connected. There are only the raw polygon objects with
>> coordinate data.
>>     
>
> Do you mean the multipolygon information which polygons belong to the 
> mulitpolygon relation is not available?
> Or do you mean that there are no tags (like natural=forest) available?
>   
At this stage there are no tags and not relations. This information has 
gone. It is converted to single independent polygons which should be 
displayed in the map. They are represented as java objects of given type 
(MapLine?, MapArea?  Sorry, haven't the correct names in mind) This 
elements have only information of how to be encoded in garmin types.

>   
>> In my very private opinion the multipolygon handling should be done in
>> the first stage, at it is now, and the splitting should be done in the
>> filter chain after size and dp filter. But I see, that this could be
>> problematic, as the splitting has given some performance boost to the MP
>> code, so it will not be easy to extract this part of it.
>>
>>     
>
> Extracting this part should not be the problem. But I cannot say 
> anything about performance. This has to be tested.
>
> At the moment I will try to finish the mp code where it is. This should 
> improve the situation very much compared to the current trunk.
>
>   
I agree with you.
> After that we can start to move the splitting code to the filter chain 
> which sounds like a good idea.
>
>   
I think Steve is right with his suggestion to introduce a new map 
element 'multipolygon'. This seems to be a reasonable way.

Regards,
Johann