[mkgmap-dev] Analysis of MP issues in Finland

Fri Jan 29 20:30:26 GMT 2010

Hi Marko,

> Hi WanMil, Mark, all,
>
> I analyzed all the multipolygon errors and warnings I got for today's
> finland.osm.bz2 from Geofabrik, without --generate-sea.

that's great!!

>
> Most of them can apparently be blamed on missing boundary information.
> I wrote the relation IDs an explanations to my logging.ignore file, so
> that I will not have to see these messages again.  You can get the file
> from http://www.polkupyoraily.net/osm/,
> but I will repeat the interesting bits here:
>
> # overlapping lines in multipolygons, should be fixed in mkgmap later
> http://www.openstreetmap.org/browse/relation/48542
> http://www.openstreetmap.org/browse/relation/367049
> http://www.openstreetmap.org/browse/relation/372975
> http://www.openstreetmap.org/browse/relation/387793
> http://www.openstreetmap.org/browse/relation/389976
> # multipolygon problem at tile border, should be fixed in mkgmap or splitter
> http://www.openstreetmap.org/browse/relation/302897
> http://www.openstreetmap.org/browse/relation/306274
> http://www.openstreetmap.org/browse/relation/311221

Ok, the number is quite small. Finnland contains ~2300 multipolygons. So 
the result is not too bad :-)

>
> (the offending tile border is at lat=62.226562;
> the other one is at lat=64.819336)
>
> I could not see what is causing the following issues.
> WanMil, can you please analyze these?  One of them was edited recently,
> but the other was not, as far as I can tell:
>
> 2010/01/29 12:11:44 WARNING (MultiPolygonRelation): 63240001.osm.gz: Multipolygon http://www.openstreetmap.org/browse/relation/372970 contains intersected or overlapping ways
This mp was changed today (Jan 29th 2010, 06:33). Before the change a 
small polygon in the north of the mp touched the outer ring. So it 
contains to your first category overlapping lines.

> 2010/01/29 12:11:44 WARNING (MultiPolygonRelation): 63240001.osm.gz: Multipolygon http://www.openstreetmap.org/browse/relation/375636 contains intersected or overlapping ways
The inner and outer tags are interchanged. Mp could autodetect this but 
only if it disregards the inner and outer tags completely. This makes 
problems with your next examples, because the wrong assigned inner 
polygons would be autodetected as outer polygons.

>
> Last but not least, here is an idea for quality control.
> I came across two lakes whose islands were in another lake
> (the change message hinted that the lake had been split).
> There is no warning for that.  The errors must be coming
> from missing boundary information in the Geofabrik extract.
>
> http://www.openstreetmap.org/browse/relation/303320
> http://www.openstreetmap.org/browse/relation/303321

Yep. At the moment the mp code is quite unspecific with its warning 
messages. "Multipolygon http://www.openstreetmap.org/browse/relation/xxx 
contains intersected or overlapping ways" is the only message if 
something is not correctly inner/outer tagged, or some ways are 
overlapping or inner ways belong to a complete other mp. I will think 
about how to improve this.

>
> Best regards,
>
> 	Marko

Well done!
WanMil

P.S.: I will start to analyze the mp seabounds treatment and will post 
it soon.