[fdo-internals] Re: FDO raster image data model does not provide the actual number of bits used by certain image data formats (Re: FdoRfc1 & FdoRfc2)

Frank Warmerdam warmerdam at pobox.com
Thu Mar 22 12:47:58 EDT 2007

Greg Boone wrote:
> Hi Frank,
> I took a second look at the possibility of implementing computational
> functions on the FdoRasterDataModel. 
> I finally 'clued in' that FdoRasterDataModel is not actually implemented
> at the provider level. Since it is not an interface, it is implemented
> only at the FDO API level and is meant to be an information type object
> created by the provider OR a client of the provider and set through
> FdoIRaster::SetDataModel. 
> Such a mechanism allows the provider implementation to set the default
> raster data model when the FdoIRaster instance is generated by the
> provider. It also allows the client to manipulate the raster image by
> changing its data model once it obtains access to FdoIRaster. By setting
> the values in the data model, a client would affect the information
> returned from FdoIRaster::GetStreamReader.
> Once I remembered the details, I would now suggest that a computational
> action such as GetMinMax would be better specified on the FdoIRaster
> interface itself, and have it be separated from the definition of the
> data model.


Excellent point.  At one point I meant to check if this was something that
the provider actually derives an implementation of, or not, but I never
got to it.  If we removed the concept of computation from

> I would still argue that having both MinMax and BitsUsedPerPixel is a
> more flexible system. It should be up to the client to determine what
> information is relative to their needs and make the appropriate API
> call.

OK, please go ahead and make a case for doing both.  Off hand, seems
like duplication and unnecessary complexity.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org

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