[mkgmap-dev] Bogus warnings about intersected ways in multipolygons

Tue Jan 26 19:00:35 GMT 2010

Hi WanMil,

thank you for having a look.

On Tue, Jan 26, 2010 at 07:05:39PM +0100, WanMil wrote:
> > On Mon, Jan 25, 2010 at 09:39:56PM +0000, Adrian wrote:
> >> I don't think these warnings are bogus. Mkgmap definitely has problems
> >> with multipolygons. The Languedoc-Roussillon extract (southern France)
> >> from Geofabrik provokes about a hundred of these warnings. But I believe
> >> that the intersected ways are being generated by mkgmap and that the OSM
> >> data is OK.
> >
> > That is what I meant by "bogus": the input data is correct, and mkgmap
> > is doing something wrong.  The browse URL that I posted was for a block
> > house in Helsinki, nowhere near my tile boundaries.
> >
> > 	Marko
> 
> Marko,
> 
> I tried to reproduce your problem but I wasn't able to.

Me neither.  It must have been bad map extract then, even though I can't
immediately see how.  I tried to check the history of the relation and
the ways back then, but it could be that someone had moved a node and back
again so that the dump was bad but the live data looked OK.  I did not check
the history of each node.  Or then again, this may have been fixed in
mkgmap r1512, which I ran today.  For what it is worth, this the only
message that I could find in my logs about 5828:

2010/01/23 14:24:02 SEVERE (MultiPolygonRelation): Multipolygon http://www.openstreetmap.org/browse/relation/5828 contains intersected ways

Here is another case for you:

2010/01/26 13:08:41 SEVERE (MultiPolygonRelation): Multipolygon http://www.openstreetmap.org/browse/relation/48542 contains intersected ways

The ways do not really intersect, but they overlap.  It is a Japanese
garden (leisure=garden) within a landuse=residential polygon.  Could
you omit the warning for this case, or at least replace the "intersected"
with "overlapping"?  ASCII art for the lines:

RRRRRRRRRRggggRRRRRRRR
R         g  g       R
R         g  g       R
RRRRRRRRRRggggRRRRRRRR

R=residential, g=garden.  I believe that you would get a similar situation
if a "more valid" multipolygon were cut by a tile boundary (T), like this:

RRRRRRRRRRRRRRRRRRRRRR
R                    R
R         gggg       R
R         g  g       R
TTTTTTTTTTTTTTTTTTTTTT
R         g  g       R
R         gggg       R
RRRRRRRRRRRRRRRRRRRRRR

As far as I understand, you'd have to replace the
TTTTTTTTTTTTTTTTTTTTTT with RRRRRRRRRRggggRRRRRRRR
in each tile.

I would not like to see any multipolygon warnings at tile boundaries.
I understand that it is currently impossible to silence them at the
unknown boundaries of the Geofabrik extracts, but I do get some warnings
at tile-splitter boundaries too.  Would it be possible to silence them
or somehow indicate that they occur at a tile border, so that I can
filter out the warnings?

Best regards,

	Marko