[gdal-dev] missing nulls in vrt from GRASS rasters

[Even Rouault]

William,

you didn't mention how you have generated the VRT. If it's with gdalbuildvrt, 
I've just commited a change in trunk (r17201) that probably solves your 
issue. It appears that when a source has a nodata value, it is not sufficient 
to set it at the VRTRasterBand level. It must also been specified for each 
source by using a ComplexSource instead of a SimpleSource, so that nodata 
pixels from the source are not drawned on the destination buffer.

You can fix your VRT manually by replacing all SimpleSource references by 
ComplexSource and by adding a <NODATA>256</NODATA> inside each 
<ComplexSource> element.

Note that with qgis from svn trunk, I could manage to make it display 
correctly RGB images whose bands are of type UInt16 (it displayed only 
black), even when specifying the value range as 0...255 instead of the 
default 0...65535. I had to edit manually the VRT so that the VRTRasterBands 
are declared as Byte. This appears to be a qgis issue/feature, as openev can 
display correctly the same VRT.

Regards,

Even

Le Saturday 06 June 2009 18:48:30 William Kyngesburye, vous avez écrit :
> I created a vrt raster from a set of GRASS rasters - image groups, RGB
> + nulls.  But the nulls are not coming thru in the vrt.  Individually
> I get nulls.  Viewing in Qgis the vrt looks like: