Waypoints setting with px4flow

Dear all,
I have a question about LPE with px4flow. I saw in http://dev.px4.io/optical-flow-outdoors.html that px4flow can fly according to waypoints. However, without a GPS, how does the flow know where various waypoints are? The coordinates, i.e. lon, lat, etc, need to be set before flight, or px4flow can get it on the fly. Thanks for the clarification.