mapnik/tests/visual_tests/styles/tiff-resampling.xml

<Map srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over" background-color="#ffffff">
  <Parameters>
    <Parameter name="sizes">600,400</Parameter>
  </Parameters>

<Style name="style">
  <Rule>
    <RasterSymbolizer opacity="0.1" scaling="spline36" />
  </Rule>
</Style>

<Layer name="layer"
  srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
    <StyleName>style</StyleName>
    <Datasource>
       <Parameter name="file">../data/snow-cover.tif</Parameter>
       <Parameter name="type">gdal</Parameter>
    </Datasource>
  </Layer>

</Map>