[mkgmap-dev] Warnings about hyper-precise multipolygons

Tue Mar 18 08:42:24 GMT 2014

Hi Marko,

I've checked a few cases. The typical reason for a message like this:
very small shape near http://www.openstreetmap.org/?mlat=60.261495&mlon=24.689112&zoom=17 signed area in high prec map units: 2816

is a shape close to a tile boundary or a shape that is produced by the mp-relation
routines. In the latter case, the routines cut a shape into pieces to remove holes.
Sometimes this produces micro-areas when the cutting line cuts the polygon into
multiple pieces. Nothing is wrong with the OSM data, and the ShapeMergeFilter
is able to merge these micro shapes again.
I plan to rewrite that part of the code, but it will require a bit more work, so
maybe this has to wait for the next autumn.

For now, I've just lowered the severity to debug level.

Gerd

> Date: Mon, 17 Mar 2014 22:45:54 +0200
> From: marko.makela at iki.fi
> To: mkgmap-dev at lists.mkgmap.org.uk
> Subject: [mkgmap-dev] Warnings about hyper-precise multipolygons
> 
> 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
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.mkgmap.org.uk/pipermail/mkgmap-dev/attachments/20140318/a3594c59/attachment.html>