mapnik/tests/visual_tests/styles/simplify-visvalingam-whyatt.xml

<Map background-color="white" 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">
    <Parameters>
        <Parameter name="sizes">500, 1000</Parameter>
    </Parameters>
    <Style name="lines">
        <Rule>
            <LineSymbolizer simplify-algorithm="[algorithm]" simplify="[simplify]" geometry-transform="translate(0, [ty])" />
        </Rule>
    </Style>
    <Layer name="world" 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>lines</StyleName>
        <Datasource>
           <Parameter name="type">sqlite</Parameter>
           <Parameter name="file">../../data/sqlite/world.sqlite</Parameter>
           <Parameter name="use_spatial_index">true</Parameter>
           <Parameter name="table">
               (SELECT *, 'visvalingam-whyatt' as algorithm, 10 as simplify, -375 as ty FROM world_merc UNION ALL
                SELECT *, 'visvalingam-whyatt' as algorithm, 20 as simplify, -125 as ty FROM world_merc UNION ALL
                SELECT *, 'visvalingam-whyatt' as algorithm, 40 as simplify,  125 as ty FROM world_merc UNION ALL
                SELECT *, 'visvalingam-whyatt' as algorithm, 80 as simplify,  375 as ty FROM world_merc)
           </Parameter>
        </Datasource>
    </Layer>
</Map>