[gdal-dev] GDAL appears to ignore NoDataValue

[Even Rouault]

Selon Ophir Yoktan <ophiry at gmail.com>:

Several errors :
1) The NoDataValue and HideNoDataValue elements are only valid under the
VRTRasterBand element, not SimpleSource
2) You want to change SimpleSource to ComplexSource, and add a
<NODATA>0</NODATA> element in it. (well basically rename your current
NoDataValue to NODATA.


> 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?
>