[gdal-dev] Amplitude virtual bands for complex datasets ?

Even Rouault even.rouault at spatialys.com
Mon Jul 4 02:06:20 PDT 2016

> To check if I understood well :
> I will create a driver that will recognize the
> "DERIVED_SUBDATASET:Amplitude:original_datasetname" syntax. This driver
> needs to now if "original_datasetname" is of complex type (to report it
> can open it)

That or we could also possibly accept non-complex types (assume imaginary part 
= 0). Antonio's functions handle complex & non-complex AFAICS

> , and will also expose the derived band somehow (can I
> benefit from the CreateDerivedBand API, 

If you write it, yes... (it doesn't exist yet if I wasn't clear)

If you follow the VRT pixel function road, that's a matter of building a on-
the-fly VRT dataset.

http://www.gdal.org/gdal_vrttut.html#gdal_vrttut_creation could possibly be 
used. But AFAICS setting the pixel function name isn't supported. Could be 
done by implementing CPLErr VRTSourcedRasterBand::SetMetadataItem( const char 
*pszName, const char *pszValue, const char *pszDomain ), similarly to what 
VRTSourcedRasterBand::SetMetadataItem(...) handles for vrt sources.

> and the pixel functions from Antonio ?).

Would make sense to internalize this code (uses X/MIT license)

> Also, "original_datasetname" can be a subdataset itself.

Yes, that shouldn't matter to the driver. It is just a string that it provides 
to GDALOpen() (some care must be taken when parsing 
DERIVED_SUBDATASET:algname:original_datasetname, since original_datasetname 
can have columns too)

> There should also be a mechanism that will report the existing
> DERIVED_SUBDATASETS upon query (this I did not get yet).

Implement in GDALDataset, the following method (from GDALMajorObject)

virtual char **GetMetadata( const char * pszDomain = "" );

char **GDALDataset::GetMetadata( const char * pszDomain = "" )
	if( pszDomain != NULL && EQUAL(pszDomain, "DERIVED_SUBDATASET") )
		// some stuff. Be careful that ownership of returned char** belongs
		// to the dataset object
		return GDALMajorObject::GetMetadata(pszDomain);

As well as :

virtual char **GetMetadataDomainList(); to report DERIVED_SUBDATASET when it 
makes sense (contrary to GetMetadata(), ownership of the returned char** 
belongs to the caller)


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