Geoserver Raster layer cropped by polygon?

Question

I've got a Geoserver raster layer which represents a satellite image. I use the Geoserver WMS to display the raster in OpenLayers. I want to display only parts of the raster - those within a certain region.

Is it possible to send a parameter to the server (like a bbox, or a CQL expression), which will tell it to render only within a polygon?

Can i make any 'tweaks' in OpenLayers to accomplish this behavior? For vector layers I can use a cross-layer CQL filter in the WMS request, but what to do with a raster?

Answer 1

You can do this by adding a <Transformation> section to the SLD for your raster layer, e.g.:

<Transformation>
  <ogc:Function name="gs:CropCoverage">
        <ogc:Function name="parameter">
          <ogc:Literal>coverage</ogc:Literal>
        </ogc:Function>
        <ogc:Function name="parameter">
          <ogc:Literal>cropShape</ogc:Literal>
          <ogc:Literal>POLYGON ((-100 20, -60 20, -60 60, -100 60, -100 20))</ogc:Literal>
        </ogc:Function>
  </ogc:Function>
</Transformation>

If the cropping polygon is to be specified by the user as part of the request, you can replace the cropShape constant above with SLD variable substitution.