On 21/04/2016 16:48, Jochen Topf wrote:
On Do, Apr 21, 2016 at 04:03:31 +0200, Sylvain Melin wrote:
I wrote a C++ program using libosmium to read an osm file, filter the data
and extract the result to different target shapefiles.
I have a problem with some features not being written in shapefiles.
For example, I want to extract all water bodies in the bounding box
latmin=44 latmax=45 lonmin=-1 lonmax=0.
In the resulting shapefile, the relation 2988 "Lit de la Dordogne" is
missing : https://www.openstreetmap.org/relation/2988
The osmium::Area built from this relation seems to be empty.
area.num_rings() gives 0
If there are no rings, this means the multipolygon relation is broken in some
way. There can be many different reasons why this is the case, usually
self-intersections or gaps in the rings. Or it can be a bug in the multipolygon
assembly code. You can use "problem reporters" to give you more insight into
what libosmium thinks is wrong with the area. (Sorry, currently no sample code.
If you want to know how they work, say so, and I'll whip up some examples.)
There are a few known bugs in the libosmium MP code and I am working on an
improved versions which will be ready soon. At the moment I would suggest, you
wait a few days and then try the new code, before digging further into this.
I don't want to debug the old code any more.
Sometimes the OSM Inspector can show you where the problem is:
http://tools.geofabrik.de/osmi/?view=multipolygon&lon=0.82538&lat=45.03236&zoom=9&overlays=invalid_geometry_hull,duplicate_ways,intersections,intersection_lines,ring_not_closed_hull,ring_not_closed,unconnected_end_nodes,ways,role_markers,way_end_nodes,way_nodes
In this case it doesn't say anything.
Importing my osm file in QGis or converting it with ogr2ogr gives the
appropriate result and the relation 2988 is correctly exported into the
shapefile.
Osmium will not export a geometry it thinks is invalid. Other programs are
often more forgiving. The reason Osmium is picky there, is that invalid
geometries can sometimes create problems when used later, creating rendering
errors or otherwise invalid data. It is better to get them fixed in OSM.
That being said, I have also though about an "just do it" mode that doesn't
give you any guarantees.
Jochen
Ok, I'll wait for the new version of libosmium.
In the meantime I can use ogr2ogr.
Having the possibility to force export of invalid geometry would be a
useful option, as long as the log tells you there's something wrong.
In my case, since I was filtering the data to export using the tags, and
this particular area had no tags, it wasn't processed and I had no error
messages or exception.
I realized it was missing only because it is a big river.
Thank you once again for your help Jochen.
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