Geometry transformations

This section shows how 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. Then, 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”):

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:

   

   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 within 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:

Adding the mainrd_buffer style as a secondary style for Mainrd

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

   

   Extracting start and end point of a line