I’ve come across a few good resources on GNSS which are worth sharing (because calling satellite positioning systems ‘GPS’ is so 2005).
The first is on measuring the accuracy of position information from a positioning system. I’ve always understood accuracy of positions to be probabilistic, i.e. a certain percentage of the time, the measurement will be within a certain distance of the ‘true’ value. That distance grows with the desire to be more confident about the measurement. How is that expressed constantly? Enter CEP, DRMS, 2DRMS, and R95. They are explained here (with a bit of spunk) and here (with some more math).
Finally, the EU in one of it’s many framework programs, has put out a white paper on the current and emerging state of GNSS technology. Like any good EU Framework project, it has an acronym: SaPPART, or Satellite Positioning Performance Assessment for Road Transport. It’s a great read, if you’re in to this sort of thing. And if you’ve read this far, you probably are.