[gdal-dev] Transparency using gdalbuildvrt

[Even Rouault]

Hi,

no, I don't think you can do it right now. But this would be doable by adding 
a new source to the VRT driver, something like VRTMaskSource, that would use 
the mask band of the underlying dataset for an alpha channel in the VRT. In 
areas without rasters, you'll get 0 (transparent), and in areas with rasters, 
you'll get 255 (opaque) or something more complex if the dataset has nodata 
values, or an alpha channel. This could be implemented as a new option of the 
existing VRTComplexSource too.
And an extra option of the gdalbuildvrt utility would ask the creation of this 
extra band.

You could file a track ticket with this enhancement proposal.

Even

Le Wednesday 04 March 2009 17:05:32 Jason Beverage, vous avez écrit :
> Hi all,
>
> I've been playing around with gdalbuildvrt lately and it has proven to be a
> very useful tool:)
>
> What I'm attempting to do is take multiple RGB images and treat them as a
> single image using the VRT.  This works great, but since the images are
> RGB, areas where there is no data are coming back as black.  Is there a way
> that I can modify the VRT or the code to treat the VRT as an RGBA dataset
> and somehow say "If there is no data in any bands, the alpha is 0"?
>
> Thanks!
>
> Jason