[gdal-dev] [python-ogr] GML attributes are missing

[Frank Broniewski]

Even,

merci beaucoup for your continuous help and support! Creating the fields 
on the target layer and using the feature definition from the target 
layer does indeed help :-). I even looked at the corresponding part in 
ogr2ogr.py before writing to the list but I didn't realise that this 
part was not implemented in my code. Many thanks again!

Frank


Am 25.02.2011 11:34, schrieb Even Rouault:
> Selon Frank Broniewski<brfr at metrico.lu>:
>
>> Hello,
>>
>> I have a problem when converting datasources from one format to GML.
>> Whenever I export my source datasource to a GML - datasource the
>> attributes of the features are missing in the resulting gml file. Other
>> exports to formats like shapefile, kml or geojson have the attributes
>> included. When I use ogr2ogr the gml has attributes included. So my
>> question is: What's the difference between e.g. a kml and a gml
>> outputformat and why does one have attributes and the other doesn't?
>> I tried on windows using gdal 1.8 and on Hardy 8.04 with 1.7.x, and on
>> both there're no attributes with the gml.
>
> Watching the below code, I'm in fact surprised that it actually works with
> shapefile, kml or geojson...
>
> I'm really surprised for shapefile since the call to Layer.CreateField() is
> needed to create the appropriate columns in the .DBF. For GeoJSON, from a quick
> code review, it might indeed work but you shouldn't rely on that. For KML, I
> guess you only get the Name and Description but not ExtendedData.
>
>>
>> I use the following code to transform from one format to another:
>>
>>
>> target_driver = driver_by_name(target_format_name)
>> target_datasource = create_datasource(target_driver, output_destination)
>>
>> for layer in iterate_layers(source_datasource):
>>       layer_name = layer.GetName()
>>       geometry_type = get_geometry_type(layer)
>>       target_layer = target_datasource.CreateLayer(layer_name, source_srs,
>>                                                    geometry_type)
>
> # At that point, the layer has no fields.
>
>>       feature_definition = layer.GetLayerDefn()
>
> Here you need to use target_layer.CreateField() to create the fields of the
> target_layer based on the source layer feature definition.
> Something like (untested. might need some minor adjustments on method names)
>
>         # Populate the target layer with field definitions coming from the source
> layer definition
>         for i in range(feature_definition.GetFieldCount()):
>              target_layer.CreateField(feature_definition.GetFieldDefn(i))
>
>         # Now fetch the resulting target feature definition
>         target_feature_definition = target_layer.GetLayerDefn()
>
>>       for feature in iterate_features(layer):
>
>
>>           target_feature = ogr.Feature(feature_definition)
>
> Here's the error : you create a target_feature with the source layer feature
> definition. This is bound to fail (and possibly even crash). Replace with :
>             target_feature = ogr.Feature(target_feature_definition)
>
>>           target_feature.SetFrom(feature)
>>           target_feature.SetFID(feature.GetFID())
>>
>>           if transformation is not None:
>>               geometry_reference = feature.GetGeometryRef()
>>               geometry = geometry_reference.Clone()
>>               geometry.Transform(transformation)
>>               target_feature.SetGeometryDirectly(geometry)
>>
>>           target_layer.CreateFeature(target_feature)
>>
>>
>> Full code:
>> http://paste.pocoo.org/show/344283/
>> Python test file
>> http://paste.pocoo.org/show/344284/
>
> We should probably add some testing (in the binding code possibly, or deeper in
> OGR) to check that the feature passed to Layer.CreateFeature() has a feature
> definition matching the Layer.GetLayerDefn(). I would think that most (if not
> all) drivers relies on that assumpution, although I don't see it explicitely
> documented in
> http://gdal.org/ogr/ogr__api_8h.html#301d319111285a47fe6cda6e079214f8
>
>>
>>
>>
>> Frank
>>
>>
>>
>>
>> --
>> Frank BRONIEWSKI
>>
>> METRICO s.Ã  r.l.
>> géomètres
>> technologies d'information géographique
>> rue des Romains 36
>> L-5433 NIEDERDONVEN
>>
>> tél.: +352 26 74 94 - 28
>> fax.: +352 26 74 94 99
>> http://www.metrico.lu
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
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>>
>
>
>


-- 
Frank BRONIEWSKI

METRICO s.à r.l.
géomètres
technologies d'information géographique
rue des Romains 36
L-5433 NIEDERDONVEN

tél.: +352 26 74 94 - 28
fax.: +352 26 74 94 99
http://www.metrico.lu