One or Both Foregin Keys

I am working on a design where a location for something can have:

    Fully qualified address with even building names, room numbers, and
booth numbers.
**-OR-**
    GPS location
**-OR-**
    Both

Other than triggers, is there a way to enforce this using tables and
primary keys?

I imagine an address table, and then

either a some sort of intermediate table,  in a one to many
relationship, GPS to Addresses,
or the correct columns in the address table.

Either way, I don't see a normal way to enforce EITHER or BOTH without a
trigger.

Thanks in Advance.