GPS and its application to automotive testing
GPS is now widely used for automotive testing with regard to position, speed, distance measurements, and is generally accepted as the preferred technology due to its combination of very high accuracy, flexibility, and convenience.
“Whilst there is no theoretical upper limit to how fast you can sample the GPS signal, the faster you sample, the more error you get due to noise”. So you need to trade off the measurement bandwidth you require, against the measurement noise that is acceptable.
A typical road car has a resonance of around 3Hz, so sampling at 20Hz seems like a good engineering compromise to make sure you are “not missing anything”. An analogy to this would be sampling a 3mm thermocouple with a response time of five seconds: you might sample the voltage twice a second to make sure you don’t miss any information, but there is absolutely no point in sampling it any faster.
Finally, please be cautious of directly comparing specifications of GPS systems from different manufacturers – there is a huge difference between “best case” GPS accuracy and “real world” GPS accuracy. The only way to compare the accuracy of two systems is to test them on the same day, under the same conditions, at the same time.