GPS update rates, sentence frequency

[Barry914]

Is there any difference in performance, accuracy or any other significant parameters if you juggle update rates and sentence frequency, say 4 Hz update rate and sentence frequency of once every 4th fix? Does the GPS average the 4 readings? I couldn't find anything in the data sheet about this.

[adafruit_support_mike]

The GPS module keeps data structures that record the positions of the satellites it can see. For each reading, it calculates where the satellite should be at a certain time, then checks the radio signals to see how the actual measurements match the predictions. There will usually be some small disagreement between the prediction and the direct measurement, but the module uses those errors to improve the next guess.

Taking readings more frequently improves the guesses slightly because there's less time for the prediction and the measurement to drift relative to each other between readings. After a few readings, the model error becomes vanishingly small compared to intrinsic effects (rounding errors because there are only so many bits in the digital representation of a number, signals arriving slightly out of sync to the clock, etc) and extrinsic effects (variations in atmospheric density, doppler effects, etc) though.

At that point you're pretty much averaging out the random/extrinsic errors across several readings. That's left to the programmer as a tradeoff between accuracy, effort, and power consumption.

[Barry914]

Thanks Mike.