Raster GetFeatureInfo Response Customization¶

The default output for a GetFeatureInfo request on a raster layer contains just the value of the selected pixel, one for each band of the image. For instance, in case of an application/json output format:

 {
 "type": "FeatureCollection",
 "features": [
   {
     "type": "Feature",
     "id": "",
     "geometry": null,
     "properties": {
       "GRAY_INDEX": 124,
     }
   }
 ],
 "totalFeatures": "unknown",
 "numberReturned": 1,
 "timeStamp": "2021-03-19T11:33:52.587Z",
 "crs": null
}

If the raster layer is associated with a Style based on a ColorMap, GeoServer allows to include in the output the labels of each ColorMapEntry matching the pixel. This is controlled by a VendorOption, that needs to be added inside the RasterSymbolizer holding the ColorMap.

<sld:RasterSymbolizer>
   <sld:ColorMap>
       <sld:ColorMapEntry color="#0000FF" quantity="1.0" label="low"/>
       <sld:ColorMapEntry color="#FFFF00" quantity="124.81173566700335" label="mid"/>
       <sld:ColorMapEntry color="#FF7F00" quantity="559.2041949413946" label="high"/>
       <sld:ColorMapEntry color="#FF0000" quantity="55537.0" label="veryhigh"/>
   </sld:ColorMap>
   <sld:ContrastEnhancement/>
   <VendorOption name="labelInFeatureInfo">add</VendorOption>
</sld:RasterSymbolizer>

The output produced by the above RasterSymbolizer looks as follows:

 {
 "type": "FeatureCollection",
 "features": [
   {
     "type": "Feature",
     "id": "",
     "geometry": null,
     "properties": {
       "GRAY_INDEX": 124,
       "Label_GRAY_INDEX": "mid"
     }
   }
 ],
 "totalFeatures": "unknown",
 "numberReturned": 1,
 "timeStamp": "2021-03-19T11:33:52.587Z",
 "crs": null
}

As it’s possible to see, the label’s value has been added to the output with attribute name Label_GRAY_INDEX.

The VendorOption labelInFeatureInfo supports the following values:

• add the label value is added to the normal GetFeatureInfo output.

• replace the label value replaces the pixel value in the output.

• none no label is added to the output. We obtain a normal GetFeatureInfo response.

Additionally, it is possible to customize the attribute name of the label value, by means of a second VendorOption: <VendorOption name="labelAttributeName">your custom name</VendorOption>.

Assuming to have a RasterSymbolizer like this

<sld:RasterSymbolizer>
   <sld:ColorMap>
       <sld:ColorMapEntry color="#0000FF" quantity="1.0" label="low"/>
       <sld:ColorMapEntry color="#FFFF00" quantity="124.81173566700335" label="mid"/>
       <sld:ColorMapEntry color="#FF7F00" quantity="559.2041949413946" label="high"/>
       <sld:ColorMapEntry color="#FF0000" quantity="55537.0" label="very high"/>
   </sld:ColorMap>
   <sld:ContrastEnhancement/>
   <VendorOption name="labelInFeatureInfo">add</VendorOption>
   <VendorOption name="labelAttributeName">custom name</VendorOption>
</sld:RasterSymbolizer>

we would obtain the following output, where the attribute name of the label value has been replaced by the one specified in the labelAttributeName VendorOption:

{
 "type": "FeatureCollection",
 "features": [
   {
     "type": "Feature",
     "id": "",
     "geometry": null,
     "properties": {
       "GRAY_INDEX": 159,
       "custom name": "mid"
     }
   }
 ],
 "totalFeatures": "unknown",
 "numberReturned": 1,
 "timeStamp": "2021-03-19T11:50:32.433Z",
 "crs": null
}

We have been using the JSON output format for the example above, but the two VendorOptions work for all other GetFeatureInfo output formats.