<VRTDataset rasterXSize="100" rasterYSize="100">
  <VRTRasterBand dataType="Byte" band="1" subClass="VRTDerivedRasterBand">
    <ColorInterp>Gray</ColorInterp>
    <PixelFunctionType>ones</PixelFunctionType>
    <PixelFunctionLanguage>Python</PixelFunctionLanguage>
    <PixelFunctionCode><![CDATA[
def ones(in_ar, out_ar, xoff, yoff, xsize, ysize, raster_xsize, raster_ysize, r, gt, **kwargs):
    out_ar.fill(1)
]]>
    </PixelFunctionCode>
  </VRTRasterBand>
</VRTDataset>
