[gdal-dev] GDAL appears to ignore NoDataValue

[Ophir Yoktan]

I'm trying to build a mosaic, and I rely on the NoDataValue feature to
treat some parts of the image as transparent.
However, it appears that GDAL doesn't work as expected.

I also created a very simple test case using a vrt dataset and
gdal_translate - and I get the same results (that is - the 2nd image draws
over the 1st image, ignoring "transparent areas")

I have to 100X100 image files with a white marking (different in each file)
over black background (black being exactly equal to 0)
I built a simple vrt file:

    <VRTDataset rasterXSize="100" rasterYSize="100">
      <VRTRasterBand dataType="Byte" band="1">
        <ColorInterp>Gray</ColorInterp>
        <SimpleSource>
          <SourceFilename relativeToVRT="1">a1.tif</SourceFilename>
          <SourceBand>1</SourceBand>
          <SrcRect xOff="0" yOff="0" xSize="100" ySize="100"/>
          <DstRect xOff="0" yOff="0" xSize="100" ySize="100"/>
      <HideNoDataValue>1</HideNoDataValue>
      <NoDataValue>0</NoDataValue>
        </SimpleSource>
        <SimpleSource>
          <SourceFilename relativeToVRT="1">a2.tif</SourceFilename>
          <SourceBand>1</SourceBand>
          <SrcRect xOff="0" yOff="0" xSize="100" ySize="100"/>
          <DstRect xOff="0" yOff="0" xSize="100" ySize="100"/>
      <HideNoDataValue>1</HideNoDataValue>
      <NoDataValue>0</NoDataValue>
        </SimpleSource>
      </VRTRasterBand>
    </VRTDataset>
and I run the command:

    gdal_translate mosaic.vrt mosaic.tif

The result is identical to image `a2.tif`, instead of being a combination
of `a1.tif` and `a2.tif`

I got the error using gdal 1.8 and 1.9

any ideas?
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