 This example uses a <code>ol.source.Raster</code> to generate data
  based on another source.  The raster source accepts any number of
  input sources (tile or image based) and runs a pipeline of
  operations on the input data.  The return from the final
  operation is used as the data for the output source.
</p> <p>
  In this case, a single tiled source of elevation data is used as input.
  The shaded relief is calculated in a single &quot;image&quot; operation.  By setting
  <code>operationType: &#39;ima