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@iki.fi
> To: mkgmap-dev@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
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