[gdal-dev] OSM driver won't generate feature for relation

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[gdal-dev] OSM driver won't generate feature for relation

Tim Harris

I’m trying to extract water vectors from OSM using my own local Overpass API server and OGR. It works for the most part, but there are some water features missing in my output. One particularly large omission is Lake Huron.


I put an example OSM file here: https://s3.amazonaws.com/gdal-osm-data/lake_huron.osm


I can see a <relation> in the file that corresponds to Lake Huron, it’s the last element near the end of the file, <relation id=”1205151”>. It’s got 12797 <member> elements that reference the 12797 <way> elements in the file (I think).


I’ve been looking at http://www.gdal.org/drv_osm.html and saw a few tips, like setting OGR_INTERLEAVED_READING to YES and using the example do/while loop. Here’s my Python translation:


import gdal

import ogr

import geojson

gdal.SetConfigOption("OGR_INTERLEAVED_READING", "YES")

ds = ogr.Open("test_water.osm")

feats = []

nonempty = True

while nonempty:

    nonempty = False

    for i in range(0, ds.GetLayerCount()):

        layer = ds.GetLayerByIndex(i)

        feat = layer.GetNextFeature()

        while feat is not None:


            nonempty = True

            feat = layer.GetNextFeature()

with open("output.geojson", "w") as fobj:

    fc = geojson.FeatureCollection(features=[geojson.loads(feat.ExportToJson()) for feat in feats])

    geojson.dump(fc, fobj)


When I load output.geojson into QGIS and look at the line strings and polygons, I don’t see a multipolygon for Lake Huron. I do see the outline as a bunch of line strings, but no polygon. I get a similar result if I load the OSM file into QGIS directly... no lake polygon. Just a few random smaller polygons around the perimiter. It seems like OGR just isn’t producing a feature for that last relation.


I’ve tried messing around with osmconf.ini, including using the one from the QGIS plugin “QuickOSM”. My most recent version of that file is here: https://s3.amazonaws.com/gdal-osm-data/osmconf.ini


Is there some setting I’m missing in osmconf.ini that would result in a multipolygon for the lake? The relation is there and it has a “type” tag set to “multipolygon”.

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