GpsGamePlay.com - Deviation and GPS systems?

Deviation and GPS systems?

I was running the other day and thought about the following problem: both bike riders AND runners now have GPS tools available to them. Which is more accurate? The runners are obviously moving slower than the bikers and the computer system on them is measuring smaller distance increments over a given period of time than the computer system on the biker. Does this make it more error prone or less error prone? Or neither? IE, is error in GPS simply a %% of the measurement or are there baseline distance errors that occur along with %% errors????

Public Comments

as long as they have a signal from the same # of satellites no variation ( each reading is independent of all other readings speed is calculated in the unit by the software so the better the software .... but it is such a simple calculation that error is unlikely ) ( note that the readings are dependent on the number of satellites being read and that elevation can play a role in speed calculations ---going up or downhill will cause a slight error in actual ground speed ) also there is a built in error in the GPS system used by the average consumer due to the time between readings a race team ( auto racing is using a system that cost $10,000 or so and takes multiple reading to lessen the error ) will have a different system and there is even less error in a military system ( cruise missile ) there is a purposeful error built into the system that can be turned on in times of war
error will be same in both cases. the percent that is. Also if they look at relative data minimal error. like the distance walked or the speed etc as opposed to the absoluet location.
In fact there is a randomly varying error which is *deliberately* add into the GPS signal. This error amounts to something like a 30 meter radius 'circular error' zone and is there so that our 'enemies' can't utilize the GPS system as fully as we can. (The corrections are coded on what is known as the L3 sub-band and, supposedly, only the military is capable of decoding it) 30 meters is plenty close enough for most civilian navigation but, if you need things even tighter, there is a technique called 'differential GPS' that can get you to about an inch of total accuracy. But, since your position (and thence your speed) is updated something like 20 or 30 times per second, it won't make any difference at all if you're measuring walking or cycling speeds. Doug
The amount of error is directly proportional to velocity. GPS units refresh position rapidly yet not constantly, but they show constant movement. They assume that until they receive information otherwise, you're going to be traveling in the same direction at the same speed. If you were biking along a path and turned 90 degrees suddenly, the GPS would display constant movement along your original vector, past the point you turned, and only update with accurate data when it received new information from the satellites. If you were to look at a non-road-oriented GPS track history, you would see very few right angles where there was a right angle turn: unless there was a full stop before the turn, the track will run past the turning point, then angle acutely back to the new path. What it comes down to is, the more movement occuring between satellite updates, the more error.