GPS data might be acceptable in traffic court in the near future.
http://abcnews.go.com/Technology/WireStory?id=3776057&page=1
http://abcnews.go.com/Technology/WireStory?id=3776057&page=1
Traffic ticket: GPS vs Radar
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CannondaleMan
New member
There are some problems with this.
GPS's accuracy is directly correlated to how many satellites the unit is reading signals from. The fewer satellites, the less accurate the signal.
Besides, there is a built in fudge factor regarding GPS satellites. Civilian systems are not as accurte as military systems - GPS has been run off of military-based satellites - and the government is what you might call protective of its proprietary software, therefore they protect it.
I suspect the judege will throw this out.
GPS's accuracy is directly correlated to how many satellites the unit is reading signals from. The fewer satellites, the less accurate the signal.
Besides, there is a built in fudge factor regarding GPS satellites. Civilian systems are not as accurte as military systems - GPS has been run off of military-based satellites - and the government is what you might call protective of its proprietary software, therefore they protect it.
I suspect the judege will throw this out.
Light_Mania
New member
The civilian signal is now very precise and provides absolute location data within a few meters. The intentional injection of error stopped many years ago.
The bottom line is that speed determination via GPS is exceedingly accurate if enough satellites in the right geometry are in view. Whether your GPS log would be acceptable in court is another matter entirely.
The bottom line is that speed determination via GPS is exceedingly accurate if enough satellites in the right geometry are in view. Whether your GPS log would be acceptable in court is another matter entirely.
rook
New member
So what is more accurate, a radar unit with unknown calibration or waas enabled gps device? On the high end, Racelogic makes VBOX, a gps unit accurate to within 2cm and 0.1km/h
Up here, they have made it tough to fight a ticket. Stating that only prima facie evidence can be used in determining the case, ie the testimony of and officer and radar evidence is the only form eligible right now. GPS evidence may allow you to plea it down with the prosecutor, saving you a few bucks.
Up here, they have made it tough to fight a ticket. Stating that only prima facie evidence can be used in determining the case, ie the testimony of and officer and radar evidence is the only form eligible right now. GPS evidence may allow you to plea it down with the prosecutor, saving you a few bucks.
Yeah, except that sometimes you don't speed and still pay the price. Isn't that the point? Presumably if a defendant were to bring to court GPS data that demonstrated actual speed at the time of the ticket, it would be to prove that he was not speeding (i.e. that a mistake was made and a ticket was issued incorrectly, not to help prove that he really was speeding).
Falls said:
GPS is good, but not that good. 2 cm is less than one inch!!rook said:
If you read the fine print on their Accuracy page, they're within 3 meters on absolute position - that's typical for consumer-grade GPS equipment. How they extrapolate that into mere centimeters between two points (what they're calling relative distance), I'm not sure.
In order to measure absolute position down to inches, surveyors use a combination of portable GPS units and fixed-point GPS stations with radio transmitters to determine an adjustment for the satellites at that point in time. Even a fixed-point station is always moving according to GPS when you're trying to get that level of accuracy, so what it does is take its known position (surveyed with other methods) and calculates how far off the GPS is at that exact time, and transmits that delta. Surveyors also have very expensive equipment costing thousands of dollars.
GPS is only that good with a clear sky and clear view of at least 4 satellites. (3 determine your location, and more help improve the accuracy.) Overcast, dense trees, tall buildings, and bridges/tunnels will reduce the accuracy of the calculation. Because of those variables, I don't see the GPS data holding up in court.
I think the other flaw with the GPS argument in that article is that it's saving measurements every 30 seconds. The radar gun would measure at an instant in time. It's not hard to argue that you sped up during the 30-second interval for some reason.
Of course the GPS is capable of reading faster than that, but you would have to have a way to save all of that data.
toto said:
Almost like the the same flaws with Radar gun but yet it is admissable in traffic court for so many years.
From Wikipedia.org http://en.wikipedia.org/wiki/Radar_gun
"The angle in which the object is in relation to the radar source can also affect the reading. This includes angles on a horizontal and vertical plane. This is referred to as Cosine Effect, but this effect always causes the displayed speed different to actual speed. It is suggested that interference in the RADAR band by cellular phones, transmitters of other kinds, power wires, signs and even stationary walls can create erroneous readings. This is not taken care of when a photo RADAR is used and all kinds of discrepancies can creep in. There are many websites which cover this problem."
I heard the weather too can affect on the readings. And the main thing is the USER error on Radar gun.
I dont think the GPS can have user error.
