[gdal-dev] Creating derived raster bands using python

[Even Rouault]

Forget what I told about GDALAddDerivedBandPixelFunc ... This is certainly not 
the way to define the function name.

Le Sunday 08 March 2009 20:51:46 Even Rouault, vous avez écrit :
> Antonio,
>
> There are 2 issues :
> -  the "ERROR 1: Corrupt or empty VRT source XML document." comes from the
> line 'b.SetMetadata(md, 'new_vrt_sources')'. However I'm not sure how to
> achieve what you want to do. I've the feeling you can't really define the
> pixel function that way. You should call GDALAddDerivedBandPixelFunc to do
> that, but as it is not available in Python bindings, I think you're only
> solution is to generate the whole XML at hand.
>
> - the crash comes from the fact that you don't have defined a pixel
> function for the derived band. I've created ticket
> http://trac.osgeo.org/gdal/ticket/2877 about that one.
>
> Best regards,
> Even
>
> Le Sunday 08 March 2009 13:30:05 Antonio Valentino, vous avez écrit :
> > Il giorno Thu, 05 Mar 2009 09:26:51 -0500
> >
> > Frank Warmerdam <warmerdam at pobox.com> ha scritto:
> > > Antonio Valentino wrote:
> > > > Hi list,
> > > > I'm trying to create a *Derived* raster band in a virtual dataset.
> > > >
> > > > All my attempts seems to fail:
> > > >>>> ds.AddBand(options={'subClass': 'VRTDerivedRasterBand'})
> > > >
> > > > raises an exception while
> > > >
> > > >>>> ds.AddBand(options='subClass="VRTDerivedRasterBand"')
> > > >>>> ds.AddBand(options=['subClass="VRTDerivedRasterBand"'])
> > >
> > > Antonio,
> > >
> > > I believe the correct syntax is:
> > >
> > >    ds.AddBand(options=['subClass=VRTDerivedRasterBand'])
> > >
> > > The options should be a list of name=value pairs.  Your extra double
> > > quotes within the string will make the class name comparison fail
> > > since you are effectively passing "\"VRTDerivedRasterBand\"" in C
> > > terms.
> > >
> > > Best regards,
> >
> > Hi Frank,
> > thanks for helping.
> >
> > I'm still having problems trying to create a derived raster bands via
> > python.
> > I'm using Ubuntu 8.10
> >
> > $ uname -a
> > Linux mac1 2.6.27-13-generic #1 SMP Thu Feb 26 07:31:49 UTC 2009 x86_64
> > GNU/Linux
> >
> > with GDAL 1.5.4 package from UbuntuGIS repo
> > (python-gdal_1.5.4-2~intreid3).
> >
> > The execution of the following test script produces a segmentation
> > fault:
> >
> > ### BEGIN CODE
> > from osgeo import gdal
> > driver = gdal.GetDriverByName('VRT')
> > source_xml = '''<SimpleSource>
> >   <SourceFilename relativeToVRT="1">test.tif</SourceFilename>
> > </SimpleSource>'''
> >
> > md = {'Description': 'Magnitude', 'PixelFunctionType': 'module',
> > 'source_0': source_xml}
> >
> > ds = driver.Create('test.vrt', 100, 100)
> > b = ds.GetRasterBand(1)
> > b.SetMetadata({'source_0': source_xml}, 'new_vrt_sources')
> > ds.AddBand(options=['subClass=VRTDerivedRasterBand'])
> > b = ds.GetRasterBand(2)
> > b.SetMetadata(md, 'new_vrt_sources')
> > del ds
> > print open('test.vrt').read()
> > ### END CODE
> >
> > $ python test_derivedband.py
> > ERROR 1: Corrupt or empty VRT source XML document.
> > Segmentation fault
> >
> >
> > Maybe I'm still doing something wrong but the segfault is anomalous in
> > any case.
> >
> > Should I create a ticket for this?
> >
> >
> > Regards
>
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