SLD to label linestring

Question

I am trying to get labels to follow the linestring. I have inserted the following sld text into a geoserver style, but the label is displayed at the horizontally at linestring centroid

          <sld:TextSymbolizer>

       <sld:Geometry>
          <ogc:Function name="centroid">
           <ogc:PropertyName>shape</ogc:PropertyName>
          </ogc:Function>
       </sld:Geometry>

        <sld:Label>
          <ogc:PropertyName>road_name</ogc:PropertyName>
        </sld:Label>

        <sld:Font>
          <sld:CssParameter name="font-family">MS Shell Dlg 2</sld:CssParameter>
          <sld:CssParameter name="font-size">6.0</sld:CssParameter>
          <sld:CssParameter name="font-style">normal</sld:CssParameter>
          <sld:CssParameter name="font-weight">normal</sld:CssParameter>
        </sld:Font>            

        <sld:LabelPlacement>
          <sld:LinePlacement>
            <sld:PerpendicularOffset>10.0</sld:PerpendicularOffset>
          </sld:LinePlacement>
        </sld:LabelPlacement>

        <Halo>
            <Radius>
                <ogc:Literal>2</ogc:Literal>
            </Radius>
            <Fill>
                <CssParameter name="fill">#FFFFFF</CssParameter>
                <CssParameter name="fill-opacity">0.85</CssParameter>               
            </Fill>
        </Halo>

        <sld:Fill>
          <sld:CssParameter name="fill">#000000</sld:CssParameter>
        </sld:Fill>

       <sld:VendorOption name="followLine">true</sld:VendorOption>

      </sld:TextSymbolizer>

I thought that by adding the VendorOption -> "followLine" the label would be displayed inline with the line. Is there something that i have missed in the documentation to make this work?

Answer 1

You must remove the geometry transformation turning the line into a point:

   <sld:Geometry>
      <ogc:Function name="centroid">
       <ogc:PropertyName>shape</ogc:PropertyName>
      </ogc:Function>
   </sld:Geometry>

With the above in, the code is labelling a point, not a line.