[gdal-dev] OSM - delineation of rivers

Simon Lyngby Kokkendorff silyko at gmail.com
Sun Jan 1 12:15:23 PST 2017


Thanks Even,

 I'll try to see if I can fix the issue for that particular location by
including a larger area. Was just puzzled because things were working fine
at other locations along the river, and for some other rivers, even with a
smaller area. But perhaps that's due to river polygons being smaller.
Also I was cheating a bit with osm2pgsql which was run on a much larger
area - since I thought the problem wasn't due to the area being too small.
But makes completely sense of course, that this could be the issue -
somehow assumed that the overpass API would return all "relevant" features
intersecting the bounding box.

Will test a bit more 😄

Cheers,
Simon

Den 01/01/2017 7.41 PM skrev "Even Rouault" <even.rouault at spatialys.com>:

> On dimanche 1 janvier 2017 18:17:58 CET Simon Lyngby Kokkendorff wrote:
>
> > Dear List,
>
> >
>
> > I have some issues getting river boundaries out of OSM data when using
>
> > GDAL to read e.g. an OSM xml file downloaded via the overpass API. Using
>
> >
>
> > e.g.:
>
> > >ogr2ogr -t_srs EPSG:3857 -f SQLITE -dsco SPATIALITE=YES --config
>
> >
>
> > OSM_USE_CUSTOM_INDEXING NO map.sqlite map.osm
>
> >
>
> > >ogrinfo --version
>
> >
>
> > GDAL 2.1.0, released 2016/04/25
>
> >
>
> > Specifically I have been trying with the River Thames in London. For some
>
> > parts of the river it works, and I get features in the 'lines' layer with
>
> > waterway='riverbank', that are closed. But for many locations I get no
>
> > features (lines or multlipolygons) that can be used to bound the river -
>
> > links to some images and OSM data below.
>
> >
>
> > When running the ogr2ogr command, I do get an errror:
>
> >
>
> > ERROR 1: Too many tags in relation 62149,
>
> >
>
> > which is not unusual though..
>
>
>
> I've just fixed in trunk this error, but this is not directly related to
> the issue you have.
>
>
>
> I presume osm2pgsql is more tolerant when parsing relations where some
> members are missing. Currently the OGR OSM driver gives up building a
> multipolygon as soon as a member is missing. This is my hypothesis for the
> missing geometries (that should be confirmed by identifying the OSM id of
> the objects imported by osm2pgsql and missing in OGR OSM output)
>
>
>
> This is for example the case for <relation id="28934"> "River Thames".
>
>
>
> No solution except improving OGROSMDataSource::BuildMultiPolygon() in
> ogr/ogrsf_frmts/osm ;-) or extracting a larger extent around the area of
> interest so that relations aren't truncated.
>
>
>
> Even
>
>
>
> --
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
>
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