[Gdal-dev] Re: Question of GDAL Virtual Format

[Frank Warmerdam]

Feng Wang wrote:
> Hi, Frank:
>  
> Now we have a need to display combined image with three image files as 
> red, green and blue bands.
> To do this, we want to use GDAL virtual format to simplify programming. 
> After I read the tutorial,
> I have some questions for your help.
>  
> Can we use multi <SimpleSource> </SimpleSource> to made a virtual 
> dataset like this:
>  
> <VRTDataset rasterXSize="512" rasterYSize="512">
> <VRTRasterBand dataType="Byte" band="3">
> <ColorInterp>RGB</ColorInterp>
>  
> <SimpleSource>
> <SourceFilename>Filename1.tif</SourceFilename>
> <SourceBand>1</SourceBand>
> <SrcRect xOff="0" yOff="0" xSize="512" ySize="512"/>
> <DstRect xOff="0" yOff="0" xSize="512" ySize="512"/>
> </SimpleSource>
>  
> <SimpleSource>
> <SourceFilename>Filename2.tif</SourceFilename>
> <SourceBand>1</SourceBand>
> <SrcRect xOff="0" yOff="0" xSize="512" ySize="512"/>
> <DstRect xOff="0" yOff="0" xSize="512" ySize="512"/>
> </SimpleSource>
>  
> <SimpleSource>
> <SourceFilename>Filename3.tif</SourceFilename>
> <SourceBand>1</SourceBand>
> <SrcRect xOff="0" yOff="0" xSize="512" ySize="512"/>
> <DstRect xOff="0" yOff="0" xSize="512" ySize="512"/>
> </SimpleSource>
> </VRTRasterBand>
> </VRTDataset>

Feng,

Not quite.  You need 3 VRTRasterBand objects each with a single source.
The SrcRect and DstRect elements may be omitted when the default 1:1 mapping
is being used.  So, a VRT file for composing 3 bands might look like the
following ... this examples also includes setting the color interpretation
properly though this wouldn't normally matter in RationalMapper.

<VRTDataset rasterXSize="256" rasterYSize="200">
   <VRTRasterBand dataType="Byte" band="1">
     <ColorInterp>Red</ColorInterp>
     <SimpleSource>
       <SourceFilename>red.tif</SourceFilename>
       <SourceBand>1</SourceBand>
     </SimpleSource>
   </VRTRasterBand>
   <VRTRasterBand dataType="Byte" band="2">
     <ColorInterp>Green</ColorInterp>
     <SimpleSource>
       <SourceFilename>green.tif</SourceFilename>
       <SourceBand>1</SourceBand>
     </SimpleSource>
   </VRTRasterBand>
   <VRTRasterBand dataType="Byte" band="3">
     <ColorInterp>Blue</ColorInterp>
     <SimpleSource>
       <SourceFilename>blue.tif</SourceFilename>
       <SourceBand>1</SourceBand>
     </SimpleSource>
   </VRTRasterBand>
</VRTDataset>

I have taken the liberty of cc:ing the GDAL list since this may be of
interest to others.

Best regards,

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