Using simple Math in SLD file on Geoserver?

Question

Is it possible to use simple Math in an SLD file on Geoserver? Suppose I want to read a text size property from a database and multiply its value, how can I do this?

<sld:TextSymbolizer>
    ...
    <sld:CssParameter name="font-size">
        <ogc:PropertyName>text_size</ogc:PropertyName> * 2.1
    </sld:CssParameter>
    ...
</sld:TextSymbolizer>

This simple approach obviously doesn't work, so I thought there must be some way to achieve this.

Answer 1

You can use the math functions ogc:Mul ogc:Div ogc:Add & ogc:Sub to do simple maths on properties.

So your example would become:

<sld:CssParameter name="font-size">
    <ogc:Mul>
       <ogc:PropertyName>text_size</ogc:PropertyName>
       <ogc:Literal>2.5</ogc:Literal>
    </ogc:Mul>
</sld:CssParameter>

The only issue is that technically the SLD specification may not allow you to use a function in a CssParameter. However GeoServer is much more forgiving and will allow it.

If you ever need more complex functions see the reference page.