Some of those ideas/tasks date back to 2008 when the project was its' initial embryonic stages. The idea back then was to find a way to track a P25 station geographically - for example, using multiple time and frequency sync'd USRP's (with GPSDO for location and time sync) to do time difference of arrival type location determination, or even a Roanoke Doppler style of receiver. 

Since then, Motorola TRBO and DMR has become very popular, and with it, services such as LRRP are transmitting data over some of these networks. I know that some of the Motorola APX and TRBO series radios can be set up to transmit their GPS locations in the clear, which could be easily read over the air. This has been done in other projects with TRBO, but not with P25 to my knowledge.

These are just a few ideas I threw around, Balint (with some assistance from me) implemented a great SDR Doppler RDF. It wasn't tuned for P25 but it did work well on whatever it was tuned to.. Balint since went to California and worked on another setup using a USRP and an algorithm called MUSIC that worked very well...

In short, there are many ways of determining the direction an RF signal is coming from, and then using this to triangulate a position..

Cheers,
Matt