http://www.omnistar.com/Support/SatelliteCoverageMaps.aspx
https://www.raspberrypi.org/forums/viewtopic.php?f=93&t=80436
http://gpspp.sakura.ne.jp/rtklib/rtklib.htm
http://rtkexplorer.com/another-raspberry-pi-rtklib-project/
http://www.instructables.com/id/Sub-Centimeter-GPS-With-RTKLIB/?ALLSTEPS
http://wiki.openstreetmap.org/wiki/RTKLIB-compatible_GPS_devices