Hi Elrond,there seem to be some problems with the simplification right now. But instead of simply de-activating the simplification I think we should debug the code. Of course it's fine to de-activate it for debugging :)
The problem of distorted polygons does not only appear in the overview map, it appears at all zoom levels. One problem I could identify is that the Douglas-Peucker code does remove the "closing" node of a polygon, but doesn't put it back after simplification. This might be ok for filled polygons, but for contour lines it is a problem. I've attached the patch that I use to solve that problem.
decrease_douglas_peucker_error.patch
Description: Binary data
That patch also sets the error distance for the Douglas-Peucker algorithm to 1/8th of the resolution instead of one half. In my opinion this gives much nicer results. The question here is why it is so, because you shouldn't be able to see such small errors. From looking at the Douglas-Peucker code I can not put my finger on any bug. What I do not understand is the distance calculation. Anybody with insight cares to have a look at it (or explain how it works?). I'd assume that a distance calculation on a spherical surface would involve lots of trigonometric functions - which the formula in the code doesn't.
Take care Thilo
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