[gdal-dev] Boundary issues

[Jukka Rahkonen]

Tan Hao Feng <htan <at> hsr.ch> writes:


> Dear GDAL developers,
> 
> I'm trying to display the boundary out from QGIS from the following steps.
> 
> Add Vector Layer.
>  Select Protocol and
>  insert the URL with Type as GeoJSON and select Open.
> 
> 
> 
> The URL
is http://tools.wmflabs.org/wiwosm/osmjson/getGeoJSON.php?lang=en&article=Singapore which
>  has both type "Points" and "Polygon".
> 
> Is there any way to read the Polygon file only?
> 
> Thanks!
> 
> Hao Feng.

Hi,

That GeoJSON does not contain point and polygon types, it contains only one
type and that is GeometryCollection as you can test with

>ogrinfo -ro
/vsicurl_streaming/"http://tools.wmflabs.org/wiwosm/osmjson/getGeoJSON.php?lang=en&article=Singapore"
INFO: Open of
`/vsicurl_streaming/http://tools.wmflabs.org/wiwosm/osmjson/getGeoJSON.php?lang=en&article=Singapore'
      using driver `GeoJSON' successful.
1: OGRGeoJSON (Geometry Collection)

What you can do is to write geojson into a Spatialite-db by exploding the
collections

>ogr2ogr -f SQLite -dsco spatialite=yes -explodecollections test.sqlite
/vsicurl_streaming/"http://tools.wmflabs.org/wiwosm/osmjson/getGeoJ
SON.php?lang=en&article=Singapore"

Finally you can read from Spatialite only geometries which are of type
"polygon" 

>ogrinfo test.sqlite -sql "select * from ogrgeojson where
geometrytype(geometry)='POLYGON'"

Programmers for sure know some more sophisticated ways to achieve the same
result. This is an end-user solution.

-Jukka Rahkonen-