[mkgmap-dev] Warnings about hyper-precise multipolygons

Mon Mar 17 20:45:54 GMT 2014

Hi Gerd,

>if you are talking about the messages from ShapeMergeFilter: A possible 
>reason is a self intersecting polygon. The filter assumes that shapes 
>are not self intersecting, but it doesn't test this yet.

About a week ago, I got a message that I thought was about merging 
adjacent (non-overlapping) shapes that carry identical tags. I cannot 
find such a message now. Here would be two examples of this:

http://www.openstreetmap.org/browse/relation/1225936
http://www.openstreetmap.org/browse/relation/1232121

These are hyper-precise multipolygons with two circles. Both the outer 
ring (actually, the relation) and the inner ring carry the same tag 
landuse=grass. Only the value of the golf=* attribute differs, but this 
does not matter to the default style.

There used to be two polygons for the inner circle: the role=inner 
polygon with no tags, and a duplicate polygon with the tags 
landuse=grass,golf=green. I deleted the duplicate polygon and moved the 
tags to the role=inner polygon. Tomorrow or the day after, I should see 
if the mkgmap message is changing.

There still are a few hyper-precisely mapped multipolygons, for which 
mkgmap is emitting messages. It is no problem for me to keep these 
relations in my ignore list. I usually monitor the output with "grep -vf 
logging.ignore mkgmap.log.0". Many relations that were on my ignore list 
are no longer generating errors. Either the data has been changed, or 
the higher precision is helping, or both.

	Marko