I'm using imageParameters and layerDefs to allow a user to define a query and return results. This works for attribute queries eg "Population> 40 AND Hispanic > 50". Now I'd like to sum up attribute values (eg 50+40) when the user creates this layerDef and render the sum of these values. Different sums are returned depending on the layer/attribute combination the user chooses, but they are rendered the same. Any ideas?