[mkgmap-dev] Multipolygons and basic question on polygons with holes

Sat Jan 2 21:47:41 GMT 2010

Am 02.01.2010 22:32, schrieb Johann Gail:
> Point 3 is illustrated by the second diagram, where a sea polygon is
>> split into X and Y and avoids the need for a DABC cut as in the first.
>> It may not be easy to take advantage of this with an algorithm, but
>> I'd probably make use of that a lot if doing it by hand.
>>
>>
>>      
> Sorry, but I can't see the difference. The picture on the right side
> shows a splitted polygon, but there are two places with parallel lines.
> Both polygons have concave segments too. So there is the same need for a
> DABC cut. Where is my misunderstanding?
>    
Dear Johann,

the problem in the splitter does AFAIK only occur when the overlapping 
segments are in the _same_ polygon. So the second diagram should 
(hopefully) be handled correctly by the splitter.

The splitter uses java.awt.geom.Area to do the hard stuff, so I think 
it's not so easy to fix it.

Best wishes
Christian