[gdal-dev] Need help if OGR C-API

[Stephen Woodbridge]

Thanks Even,

I coded up a similar test program, and the works here so I'm looking 
elsewhere.

Looks like ogdi on Debian installs libgdal.so so I just uninstalled 
ogdi, since I don't think I use it. And I'm rebuilding gdal without that 
just to make sure I have a clean system without any rouge libs hanging 
around.

Then I will get back to debugging this.

-Steve W

On 9/3/2010 1:43 PM, Even Rouault wrote:
> Le vendredi 03 septembre 2010 18:45:56, Stephen Woodbridge a écrit :
>> Hi all,
>>
>> Trying to convert a shapelib program over to OGR and have to say it is
>> very complicated.
>
> No, it's just that you are not yet accustomed to use it ;-)
>
>>
>> I'm using: GDAL 1.7.2, released 2010/04/23
>>
>> At the moment I stuck on:
>>
>>     hDSin = OGROpen( "Streets.shp", FALSE, NULL );
>>     hLayerIn = OGR_DS_GetLayerByName( hDSin, "Streets" );
>>
>>     hFDefnIn = OGR_L_GetLayerDefn( hLayerIn );
>>     layerGeomType = OGR_FD_GetGeomType( hFDefnIn );
>>
>> And always returns:   layerGeomType == wkbUnknown
>
> Well, this is really weird. I've just tried the following code that is really
> a stand-alone version of your code:
>
> #include<ogr_api.h>
>
> int main(int argc, char* argv[])
> {
>      OGRRegisterAll();
>      OGRDataSourceH  hDSin = OGROpen( argv[1], FALSE, NULL );
>      OGRLayerH hLayerIn = OGR_DS_GetLayer( hDSin, 0 );
>      OGRFieldDefnH hFDefnIn = OGR_L_GetLayerDefn( hLayerIn );
>      OGRwkbGeometryType layerGeomType = OGR_FD_GetGeomType( hFDefnIn );
>      printf("%d\n", layerGeomType == wkbLineString);
>      return 0;
> }
>
> when passed a shapefile with linestrings, it prints 1 as expected with both
> trunk and 1.7 branch. You should try it on your streets.shp. If it returns 1,
> so there must something subtly wrong on your code that perhaps valgrind could
> detect. If it returns 0, hum, well no idea...
>
>>
>> And OGR_L_GetGeomType( hLayerIn )  does not appear until 1.8.
>
> You don't need it. This is just a convenience method that can provide speed-up
> for some drivers. But as documented, it will be strictly equivalent to
> OGR_FD_GetGeomType(OGR_L_GetLayerDefn(hLayerIn)).
>
>>
>> ogrinfo -so Streets.shp Streets
>> INFO: Open of `Streets.shp'
>>         using driver `ESRI Shapefile' successful.
>>
>> Layer name: Streets
>> Geometry: Line String
>> Feature Count: 102958
>> Extent: (-71.888528, 42.156701) - (-71.020913, 42.734315)
>> Layer SRS WKT:
>> (unknown)
>> LINK_ID: Integer (10.0)
>> NAME: String (80.0)
>> ...
>>
>> So how do I get the geometry type of the shapefile?
>>
>> -Steve
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