I bought a 3DR radio from Whitespy to add telemetry to my MultiWii and it works like it should. Multiwii has a processing program called multiwiiconf that is used to make changes to the PID's and for selecting flight modes and reading and writing to EEPROM. There is also a slick GUI that adds a few more functions like a moving map. I've tried both and the "slick" wingui program really uses a lot of memory and processor which my computer can't spare or tolerate without catching on fire. That was my motivation for seeing what I could do to add a realtime map to the not so resource intense processing multiwiiconf program. This was easier than I expected. I searched for mapping programs and libraries already written for processing and found the modestmaps library. https://github.com/modestmaps/modestmaps-processing
I familiarized myself with the example and armed with the "//" and "/* */", I opened up the source code for multiwiiconf. My approach was to go through and comment out all the parts that pertained to PID's and graphs. Generally, I commented out anything that I thought was not related to drawing an attitude indicator, compass or reading the multiwii serial protocol. I periodically ran the sketch to see what disappeared or if I was too zealous with the comment //'s. When the only things remaining were the instruments and the com port connection buttons, I added the modestmaps library and minimal code to display a map. I replaced mouseX and mouseY with GPS_Latitude and GPS_Longitude, and divided those variables by 10000000f to convert to decimal. That little "f" made a big difference, btw. Without that I was 30 miles away because of loss of few decimal places. I also added the little green dot to show current position. This too came from the modestmaps example.
I'm telling anyone how to do it instead of posting code, since it's very simple and my code tends to appeal like a dose of clamidia. One last howto is to make sure to make the same edits in the processing sketch and the java file. If it's done the way I did it, it should work and look like this. As the position changes, the map moves with the little green position dot always in the center. It's not fancy, but it uses about 20% of my CPU instead of 100%.