<VRTDataset rasterXSize="20" rasterYSize="20">
  <VRTRasterBand dataType="Float64" band="1" subClass="VRTDerivedRasterBand">
    <Description>CustomPixelFn</Description>
    <PixelFunctionType>custom</PixelFunctionType>
    <SourceTransferType>Float64</SourceTransferType>
    <SimpleSource>
      <SourceFilename relativeToVRT="1">float32.tif</SourceFilename>
    </SimpleSource>
  </VRTRasterBand>
</VRTDataset>
