First unique thing which catalog query supports is multiple data servers which is not provided by any other query in MII. Thus in one shot you can query on multiple catalog data servers. So for other type of queries you would use the parameter in the URL as Server=<server name>. But for catalog query you can use this parameter for supplying multiple server names like this Server=<Server1,Server2>
Parameter for giving PIC objects is 'SelectedObjects'. you can use this for providing the names of PIC tags and groups with ',' as separator.
The catch here is that you have to provide names of a PIC object as <ServerName>.<Namespace of the object> (connector name with full namespace of the object)