Ok, so you mean areas that are too thin are not drawn?
yes, I added a few system.out.println and found that a lot of sea or land polygons are completely dropped by the filters, for example a polygon with 14 points was reduced two 3 points by the RoundCoordsFilter and then thrown away by another.
The mp algorithm tries to do as few cuts as possible. So it cuts at that horizontal or vertical line where it can cut the most inner polygons. It does not check if the cutting line is longer or not (because it doesn't know and it's hard to estimate without implementing your own cut algorithm).
As a first quick hack it would be possible to add a check if an area is too thin and to revert this cut. That leads to the question: Is there a definition for "too thin"?
In the tile splitter I decided that a ratio of 1:4 or less is nice, but I have no theory for that.
yes, I agree. So I'll try to find a better mp algorithm.
All you have to do is to improve the private List<Way> cutOutInnerPolygons(Way outerPolygon, List<Way> innerPolygons) method in class MultipolygonRelation. Good luck!
OK, thanks. Let's see... Gerd