Am 02.01.2010 15:18, schrieb Christian Gawron:
Am 02.01.2010 00:19, schrieb Steve Ratcliffe:
[...] Some observations
1. The sea polygon is probably cut up into small enough pieces first, before the "cuts" to the hole are made. 2. Because we do things the other way round, we make the cut a slight wedge shape, as you cannot send polygons that have touching segments to the polygon splitting code. This is what makes things look bad. 3. If you split a sea polygon with a line that goes "through" (around) a hole then you don't need to add a cut. 4. Its probably easier to do it by hand, but that might just reflect my lack of knowledge of GIS algorithms in this area...
I think it should not be too hard to create an algorithm that decomposes a polygon with holes into polygons without holes. I googled for "polygon decomposition" and found a paper describing an algorithm to decompose a polygon with holes into convex polygons, but this seems to be more than we need (and too complex computationally). Right now I have some time so I will have a look at it.
Best wishes Christian
Christian, I think it's a good idea to change the strategy from the old "polygon with holes" to "simple polygons". The old strategy does not work with the PolygonSplitter and seems to be too complex. I have some requirements to the new strategy: * It should handle most of possible cases. Otherwise we will always have complaints about not supported multipolygons. * It should take not too much performance. The current findCpa method is a performance killer for polygons with lots of points. * It should work with the current PolygonSplitter. This is achieved by creating simple polygons. At the moment I am using your idea of simple polygons and try a new implementation using the java.awt.Area class that is also used in the PolygonSplitter. I hope this will achieve the requirements. WanMil