Geometry transformations

This section show how to GeoServer provides a number of filter functions that can actually manipulate geometries by transforming them into something different: this is what we call geometry transformations in SLD.

Extracting vertices

  1. Using skills learned in the adding styles section, create a new style named mainrd_transform using the following SLD:

    <?xml version="1.0" encoding="ISO-8859-1"?>
    <StyledLayerDescriptor version="1.0.0"
      xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc"
      xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd">
      <NamedLayer>
        <Name>Roads and vertices</Name>
        <UserStyle>
          <FeatureTypeStyle>
            <Rule>
              <LineSymbolizer>
                <Stroke />
              </LineSymbolizer>
              <PointSymbolizer>
                <Geometry>
                  <ogc:Function name="vertices">
                    <ogc:PropertyName>the_geom</ogc:PropertyName>
                  </ogc:Function>
                </Geometry>
                <Graphic>
                  <Mark>
                    <WellKnownName>circle</WellKnownName>
                    <Fill>
                      <CssParameter name="fill">#FF0000</CssParameter>
                    </Fill>
                  </Mark>
                  <Size>6</Size>
                </Graphic>
              </PointSymbolizer>
            </Rule>
          </FeatureTypeStyle>
        </UserStyle>
      </NamedLayer>
    </StyledLayerDescriptor>
    

    Note

    The CSS equivalent of this style is:

    * {
      mark: symbol(circle);
      mark-geometry: [vertices(the_geom)];
      mark-size: 6;
      stroke: #000000;
      :nth-mark(1) {
        fill: #FF0000;
      }
    }
    

    Note

    The vertices function returns a multi-point made with all the vertices of the original geometry

  2. Using skills learned in the adding styles section, modify the styling of the Mainrd layer and add mainrd_transform as an alternate style (hint, select the mainrd_transform style in the first list below “available styles” and then use the right arrow to move it in the “selected styles”):

../_images/tx_secondary_style.png

Adding the mainrd_transform style as a secondary style for Mainrd

  1. Use the Preview link to display the Mainrd layer, then open the options box and choose the alternate style from the drop down:

    ../_images/sld_transform2.png

    Extracting and showing the vertices out of a geometry

Line buffer

  1. Using skills learned in the adding styles section, create a new style mainrd_buffer using the following SLD

    <?xml version="1.0" encoding="ISO-8859-1"?>
    <StyledLayerDescriptor version="1.0.0"
    xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc"
    xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd">
      <NamedLayer>
        <Name>Roads and vertices</Name>
        <UserStyle>
          <FeatureTypeStyle>
            <Rule>
              <PolygonSymbolizer>
                <Geometry>
                  <ogc:Function name="buffer">
                    <ogc:PropertyName>the_geom</ogc:PropertyName>
                    <ogc:Literal>200</ogc:Literal>
                  </ogc:Function>
                </Geometry>
                 <Fill>
                  <CssParameter name="fill">#7F7F7F</CssParameter>
                  <CssParameter name="fill-opacity">0.3</CssParameter>
                </Fill>
              </PolygonSymbolizer>
              <LineSymbolizer>
                <Stroke />
              </LineSymbolizer>
            </Rule>
          </FeatureTypeStyle>
        </UserStyle>
      </NamedLayer>
    </StyledLayerDescriptor>
    

    Note

    The CSS equivalent of this style is:

    * {
      stroke: #000000;
      stroke-opacity: 1.0, 0.0;
      fill: #7F7F7F;
      fill-opacity: 0.0, 0.3;
      fill-geometry: [the_geom], [buffer(the_geom, 200)];
    }
    

    Note

    The buffer function builds a polygon of all the points that are withing the specified distance from the original geometry.

  2. As done previously, modify the styling of the Mainrd layer and add mainrd_buffer as an alternate style:

../_images/tx_secondary_style_buffer.png

Adding the mainrd_buffer style as a secondary style for Mainrd

  1. Use the Map Preview to preview the new style.

    ../_images/sld_transform1.png

    Extracting start and end point of a line