[gdal-dev] OGR_Dr_Open deprecated

[Even Rouault]

Le vendredi 13 novembre 2015 15:17:40, Ari Jolma a écrit :
> On 13.11.2015 15:58, Even Rouault wrote:
> > Le vendredi 13 novembre 2015 14:48:02, Ari Jolma a écrit :
> >> OGR_Dr_Open became deprecated in 2.0 but it is still the main method to
> >> open vector datasets in the bindings.
> >> 
> >> I just realized that I would need one method to open all data sets.
> >> OpenEx seems to be it but I would still need to cast the object into a
> >> Dataset or a DataSource.
> > 
> > Just don't cast. You can use a Dataset for all purposes since the
> > OGR_DS_XXXX API has been transposed to GDALDatasetXXXX and is already
> > available in GDALDatasetShadow
> 
> Swig imposes typechecks that prevent that. It is like with the GDALGrid,
> which takes a vector dataset.

Not sure if it is a "swig" limitation, or something in the Perl bindings. But 
the Python and Java bindings for sure can use the vector part of 
GDALDatasetShadow.

> I had to write an explicit cast function
> for DataSource object into a Dataset object. Which I now realize is
> probably not safe since there is an explicit warning against that in the
> docs.

At the C level, you can technically cast a GDALDatasetH to a OGRDatasourceH 
since the OGR_DS_ C functions end up calling methods of GDALDataset class. But 
you cannot cast a GDALDataset* to a OGRDatasource* since OGRDatasource* has a 
few virtual methods not available in GDALDataset*

> 
> >> Maybe OpenEx should be the preferred way to
> >> open any data set also with the bindings.
> >> 
> >> However, I don't seem to find good way to tell whether the data set
> >> object OpenEx gives me is a raster or a vector. Is there such?
> > 
> > If you open with OpenEx(filename, OF_VECTOR), so read-only + vector, then
> > the few drivers that support vector and raster will return NULL if the
> > dataset has no vector data and just raster. If you open with
> > OpenEx(filename, OF_VECTOR | OF_UPDATE) and they support update mode,
> > then they will return non-NULL even if the dataset has no vector data. A
> > robust way of checking if there's vector data is to check
> > GetLayerCount() != 0.
> 
> Thanks.
> 
> I have so far ignored the OpenEx method. I'll develop it so in the Perl
> bindings that it will return a raster dataset object or a vector data
> set object depending whether the returned handle is raster or vector.
> I'll also deprecate the old Open methods in the Perl bindings.
> 
> Ari
> 
> > Even

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com