[mkgmap-dev] Possible solution for deformed polygons

Mon Nov 18 22:15:04 GMT 2013

Hi all,

at the end of 2012 we discussed "Polygons deformed", see
http://www.mkgmap.org.uk/pipermail/mkgmap-dev/2012q4/016010.html

As already mentioned the rounding to map units can cause
extreme errors in angles for points which are very close together.
This is often the case in buildings, and also the angles in buildings
are often right angles (90°), so errors are very obvious.

I think I have a possible improvement for it:
1) merge polygons with equal types etc. like in merge-lines algo,
so that e.g. buildings that share walls are combined to one polygon (without 
creating holes). 
See e.g.
http://www.openstreetmap.org/browse/way/118911628
Merging allows to merge many building polygons to one, 
this makes it less likely that two points are close.
2) Detect and remove wrong angles with an algo similar to that used in r2829 
to remove wrong angles in roads. 

I see two advantages:
a) img files which are a bit closer to OSM data
b) smaller img files (because of the merging)

I see one small possible problem:
The size filter might not remove merged polygons.

Do you see other problems?

Gerd

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