[mapguide-users] Future Raster support - transparency?

[Frank Warmerdam]

Andy Morsell wrote:
> Frank and Autodesk,
> Will the GDAL raster provider or the Autodesk raster provider have 
> support for transparency in non-bitonal imagery? 
> 
> The fact that the existing MapGuide 6.5 and below does not support this 
> has been a major problem for several of my clients.  The problem that 
> arises is that tiled imagery is often obtained from a source in one 
> coordinate system and then is transformed to the desired map coordinate 
> system.  This results in black "wedges" along all of the edges of the 
> resultant orthogonal image.  MapGuide 6.5 does not allow you to specify 
> a null color value (to non-bitonal images) so when image tiles are 
> viewed together, the sliver from one image blocks part of another 
> image.  To get around this, the clients have had to spend a large amount 
> of time, resources and money (for special image software) pre-processing 
> the imagery.  We end up having to mosaic the projected images and then 
> tiling back out into orthogonal pieces.

Andy,

The proprietary raster provider has support for returning no data values to
the higher level code.  I haven't tracked through MapGuide OS to see if these
are used.  I'm not sure if GDAL returns nodata values properly yet, but it
will before it's final release.

I would add that the FDO raster layer also supports returning RGBA images.
The alpha channel can be used to indicate transparency.  In some cases I
have found use of "alpha" transparency to be superior to use of nodata
values.

So, in short, I don't know if this will all work yet, but it is intended
to work.

Bob or someone else at Autodesk might want to indicate how transparency
works with the proprietary driver.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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