[gdal-dev] Unable to extract features from KML

[Michael Z Freeman]

Hi,

Thanks for this !

I eventually realised that I'd got in a muddle because I had failed to
understand what "wkb_geometry" is (
https://en.wikipedia.org/wiki/Well-known_text ). I think I thought it was
the gdal way for setting the SRID or something like this. So after seeing
the light I am using ...

ogr2ogr -f PostgreSQL PG:"dbname=original_hirise" -nlt geometry
MC-01-0-0-0_1.kml

SELECT ST_AsText(wkb_geometry) FROM mc_01_0_0_0_1;

... shows ...

GEOMETRYCOLLECTION(POINT(-30.415 88.0473),POLYGON((-28.14 87.938,-31.75
87.9205,-32.947 88.1536,-28.884 88.1731,-28.14 87.938))).
[...]

I'll be using PHP so the multigeometry should be fine for the moment and
seems easy enough to access ...

SELECT * FROM mc_01_0_0_0_1 WHERE
ST_DWithin(ST_CollectionExtract(wkb_geometry, 1),
ST_SetSRID(ST_MakePoint(-30.332,87.4992), 4326), 0.2);

... which gives two results with the correct coordinates.

Sorted ! (as we say here).

Best

Michael Z Freeman

On Mon, November 21, 2016 7:30 am, jratike80 wrote:
> Hi,
>
>
> The main problem is that KML support such data models which do not suit
> well with the simple feature model of GDAL. You can get some information
> about that by reading http://www.gdal.org/drv_libkml.html.
>
> In your case each feature has two geometries: one point and one polygon.
> Best that can be done with the simple feature model it to push them both
> into one geometry which in that case must be a geometry collection. Here
> is one example from your data
>
> GEOMETRYCOLLECTION (POINT (-1.282 87.1064),POLYGON ((3.02457
> 87.0792,2.22294
> 86.9806,-5.655 87.1168,-5.098 87.2201,3.02457 87.0792)))
>
>
> You can save geometry collections into PostGIS if you use ogr2ogr with
> switch "-nlt geometry". However, saving geometry collections into PostGIS
> may not solve your problem because only few GIS programs can handle
> geometry collections well.
>
> A better option for you might be to explode the collections and save
> points and polygons as separate features into PostGIS. The ogr2ogr command
> to use is like
>
> ogr2ogr -f PGDump output_pgdump -nlt geometry -explodecollections
> Beyer_Hirise_Areas_KML/MC-01-0-0-0.kml
>
>
> If you want to have a quick look at your data, use JML as outputformat
> and open the result with OpenJUMP. It shows both the geometry collections
> and exploded collections fine for me with names and descriptions.
>
> -Jukka Rahkonen-
>
>
>
>
> --
> View this message in context:
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