On-the-Fly Raster Processing and SLD Application in GeoServer

GeoServer GeoServer User
,
1

Dear [GeoServer Support/Community],

I am seeking guidance on whether it is possible to perform an on-the-fly raster calculation in GeoServer to visualize a filtered layer on the map with Openlayers.

Specifically, I am interested in executing an operation similar to the following GRASS GIS r.mapcalc expression:

if(slope_450m_4326@PERMANENT >= MIN_SLOPE_VAL && slope_450m_4326@PERMANENT <= MAX_SLOPE_VAL, sea_depth_450m_4326@PERMANENT, null())

Where MIN_SLOPE_VAL and MAX_SLOPE_VAL values are user input.
Additionally, I would like to know if such an operation can be achieved through the application of an SLD style, like the application of a filter on a single layer. If GeoServer does not support this functionality directly, I would greatly appreciate your advice on the best method to achieve this result.

Thank you for your assistance and expertise on this matter.

Kind regards,
Sara

2

We recently needed to do this as well. We ended up using the Jiffle transformation in the SLDs of the rasters like so:

  <ogc:Function name="ras:Jiffle">
	<ogc:Function name="parameter">
	  <ogc:Literal>coverage</ogc:Literal>
	</ogc:Function>
	<ogc:Function name="parameter">
	  <ogc:Literal>script</ogc:Literal>
	  <ogc:Function name="Concatenate">
		<ogc:Literal>
		  value = src[0];
		  if (value &lt; 
		</ogc:Literal>
		<ogc:Function name="env">
		  <ogc:Literal>minimum</ogc:Literal>
		  <ogc:Literal>-9999</ogc:Literal>
		</ogc:Function>
		<ogc:Literal>
		   || value &gt;
		</ogc:Literal>
		<ogc:Function name="env">
		  <ogc:Literal>maximum</ogc:Literal>
		  <ogc:Literal>9999999</ogc:Literal>
		</ogc:Function>
		<ogc:Literal>
		  ) {
			value = -9999;
		  } else {
			dest = value;
		  }
		</ogc:Literal>
	  </ogc:Function>
	</ogc:Function>
  </ogc:Function>

You just have to make sure the minimum/maximum values are sent as env parameters in the requests: &env=minimum:10;maximum:100

Hope this helps

3

Thank you so much for your helpful code!! I also ended up adding this rule in the SLD of a raster

<sld:Rule>
    <sld:RasterSymbolizer>
        <sld:Opacity>1.0</sld:Opacity>
        <sld:ColorMap>
            <!-- Valori minori di maxDepth (opacità 0) -->
            <sld:ColorMapEntry color="#FFFFFF" quantity="${env('maxDepth', -2000)}" label="Below Max Depth" opacity="1"/>
            <!-- Valori tra minDepth e maxDepth -->
            <sld:ColorMapEntry color="#0000FF" quantity="${env('maxDepth', -2000)}" label="${env('maxDepth', -2000)}" opacity="0"/>
            <sld:ColorMapEntry color="#0000FF" quantity="${env('minDepth', -100)}" label="${env('minDepth', -100)}" opacity="0"/>
            <!-- Valori maggiori di minDepth, (opacità 0) -->
            <sld:ColorMapEntry color="#FFFFFF" quantity="${env('minDepth', -100)}" label="Above Min Depth" opacity="1"/>
          
          <sld:ColorMapEntry color="#FFFFFF" quantity="0" label="Below Zero" opacity="1"/>
          <sld:ColorMapEntry color="#f7fbff" quantity="0" opacity="0" label="0"/>  
        </sld:ColorMap>
    </sld:RasterSymbolizer>
</sld:Rule>

I was wondering if it would be possible to apply the same principle but filtering one raster on another one. For example, given a filtered raster, could the same ‘no-data value mask’ be applied to another raster with the same resolution? Do you have any further advice?

Thank you so much again !!