cjh7z4
commented
7 years ago https://www.google.com/patents/US5323322 This has a good explanation of how the gps system works and how differential gps works. So basically we use a GPS at a know location, the base station and a GPS on the Rover. We look at errors in the position of the base station and we correct for the same errors in the position of the rover. since they are close, the error should also be close. To me its kind of like a system response h(t). the system being the error generated by satellite position, ionospheric and tropospheric wave-front delay and errors in wave measurement. h(t) can be found by looking at differences between know and gps generated position and then this h(t) can be used with the gps position on rover to correct for better positioning. so In my mind there are several problems to work.
How to get an accurate position at base station
How to write code to characterize h(t) and how to send this to rover? Is this allowed during autonomous portion? It will involve communication over the network
Did a few measurements of GPS drift today:
It's not just a Gaussian noise distribution like I had expected- the drift is smoothly progressing. Right now my theory is that the drift is caused by factors outside the GPS, like satellite movement and atmospheric conditions. For two identical receivers in nearby locations, I think the drift progression will look very similar.
To test this, we need to get two identical NEO-6M GPS units, place them about 20 meters apart in a parking lot, and record the drift functions. Run a statistical correlation on the data sets. If the statistical correlation is greater than about 0.8, then it means that my hunch was right.
If my hunch was right, then we can put a GPS unit on the base station (with a known fixed GPS location), calculate the drift from that, the subtract the drift from the on-rover measurements to substantially improve accuracy.