[mkgmap-dev] Merge areas

Tue Apr 26 20:55:30 BST 2011

>> Do you have a short draft how you want to detect that two areas are
>> touching?
> When two nodes follwing each other from one polygon are inside the other. Or on the outline of it.
>
>
Yeah, and you will have to test some 100 thousands of nodes, if they lie 
inside one of a 10 thousands polygons. This will be as a number of thumb 
10 ^ 9 tests (or add some more zeroes) of tests if the is node in 
polygon area, which is not a cheap test by itself.

You will need at least some tricks with quadtrees or bounding box checks 
to achieve reasonable runtimes.

In general I really like the idea of merging polygon areas. I have 
mentioned it already in this mailing list. But up to now I haven't found 
any practicable solution. The algorithm should merge two polygons even 
if there is some space between it. Think of a map of small woods or 
lakes, which should be combined to a bigger one and simplified, while 
zooming out of the map. They are *not* overlapping or touching in most 
of the cases.

I don't want discourage you, if you think, you have some working 
solution, please let us know.

Regards,
Johann