[mkgmap-dev] [PATCH v2] Remove LineClipper artefacts

Tue May 24 17:16:04 BST 2011

> I am not sure if this comes from updating mkgmap-trunk from r1946 to
> r1953 or from this patch v2, but I get these additional warnings:

This patch is unsuspicious because AFAIK the LineClipper is only used 
after the multipolygon code. So it should not change anything.

But the commit for r1953 has changed the handling how unclosed ways in 
multipolygons are closed. This code can just guess how these ways should 
be closed. So each change might remove some problems but also add some 
new ones.

>
> 2011/05/23 22:51:09 WARNING (MultiPolygonRelation): 63240002.osm.gz:
> Cannot join the following ways to closed polygons. Multipolygon
> http://www.openstreetmap.org/browse/relation/36306
> 2011/05/23 22:53:04 WARNING (MultiPolygonRelation): 63240004.osm.gz:
> Cannot join the following ways to closed polygons. Multipolygon
> http://www.openstreetmap.org/browse/relation/38101
> 2011/05/23 22:54:18 WARNING (MultiPolygonRelation): 63240006.osm.gz:
> Cannot join the following ways to closed polygons. Multipolygon
> http://www.openstreetmap.org/browse/relation/900367
> 2011/05/23 22:54:18 WARNING (MultiPolygonRelation): 63240006.osm.gz: -
> way: http://www.openstreetmap.org/browse/way/57746082
> 2011/05/23 22:54:18 WARNING (MultiPolygonRelation): 63240006.osm.gz:
> Multipolygon http://www.openstreetmap.org/browse/relation/900367 does
> not contain any way tagged with role=outer or empty role.
>
> I took a look at these relations in JOSM (ctrl-L, enter
> http://api.openstreetmap.org/api/0.6/relation/900367/full
> and so on).
>
> Relations 36306 and 38101 are boundary relations, which include some
> maritime borders in the south. They might not be completely inside the
> Geofabrik extract of Finland. I do not care about them.
>
> The outer line of 900367 (one of the multipolygons for Lake Saimaa)
> carried natural=water, which I now removed, as the multipolygon relation
> already carries that attribute.  The roles of the relation are correct:
> all member ways are either role=outer or role=inner. JOSM does not
> complain.  I guess that mkgmap is just dropping the role=outer line,
> because it is incomplete in the tile:
>
> 63240006: 2832510,1317344 to 2916352,1462272
> #       : 60.779070,28.267136 to 62.578125,31.376953
>
> The bbox of the role=outer way is 62.69143,28.0395 to 62.516,28.46425.
> That is, the outer line is slightly inside the tile. To be exact, the
> following nodes (two bays) of the outer way are inside the tile:
>
> 244270918 244272962 244270916 244272960 244270922 244270920 244272964 244270915 244270919 244272963 244272961 244270923 359093973 244270921

I cannot say for sure because I have to check that in detail but the 
following problem might have happened. The autoclosing does not longer 
prefer closing ways to connecting ways. So maybe the incomplete outer 
way was connected to an incomplete inner way and therefore the way could 
not be closed and is therefore abandoned. Maybe the algorithm should 
prefer connections of ways with an identical role or better it should 
not connect ways with non identical role.

Sounds good. I will post a patch.

>
> One island is partly at the NW corner of the tile: way 26228126. The
> other bay does not contain islands in the map data. Now, let me check
> 62.578125,28.2671360 in the generated map. Sure enough, a section of the
> lake is missing SE of the island. I guess it is showing just the
> background there.
>
> Am I right that this is a splitter problem (possibly fixable by
> increasing the split-radius)?

In the end all of (or better most of) the multipolygon problems where 
well defined mps are not correctly handled by mkgmap are caused by 
splitter generating incomplete mps.

WanMil

>
> 	Marko
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