GPS
One of the first enabling technologies for UAVs was a good localization system. GPS evolved out of military networks first conceived in the 1960's with plans for missile guidance. 24 or more low-orbit satellites are currently used to triangulate a fix with a ground unit using speed-of-light calculations. Since implementation, it has been supplemented by ground station correction like the public WAAS and several private networks, and had some of its military encrypted precision unlocked for consumer use. A-GPS, where the 'startup time' for gathering the basic schema necessary to generate satellite fixes is transmitmted on demand through a cellular network, is becoming more common. Other national systems, Europe's Galileo, Russia's GLONASS, and China's COMPASS, are coming online presently or in the next several years, and some units are capable of redundantly using several satellite networks.
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[edit] Common Models
- ublox vs mediatek - NerdyFirefighter
[edit] Improvement
There is much interest in improving the precision & accuracy of GPS, especially since the methods that professional survey-grade devices use to do so may be technically possible on the same hardware as consumer-grade devices. GPS signals drift because of turbulence in the atmosphere and orbital perturbations. Post-processing DGPS, the easiest method for getting an accurate moving log, uses a fixed unit (which can average out its position) and a mobile unit, and calculates the offset. Unfortunately, this is not directly usable with stock units, because of the chance that the two units will use different satellites, introducing a bias - the minimum GPS unit for DGPS is one which logs "pseudorange" to each satellite, so that you can throw out fixes that only reach one unit.
- If you are interested in RTK this is for you - Stephen Jack
- DGPS with RTKLIB basics - Peter N
- Max2769: RTK GPS for all? - Jack Crossfire
- Realtime DGPS with ublox and GPSTk lib processing, relative <1m? - Noland
- DGPS with my local Ground Station? - Jason Larocque
[edit] Redundant Logging
In testing vehicles, one wants to be able to make sure that their logs will survive even if the vehicle or the wireless signal does not. There are several small logging GPS devices available now, targetted at the athletic market or as USB accessories.
[edit] Software
GPS tracks are simply lists of coordinates, times, and perhaps some other precision information. Only very basic functions are necessary to look at GPS tracks, so freeware like Google Earth will often serve just fine, but it may be worthwhile to explore how they correspond to other data in a specialized desktop suite, a Geographic Information System. In a pinch, even Excel can be used to get a rudimentary idea of what occurred on a flight.
