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Radar Beats GPS In Court — Or Does It?
TechnologyResource writes "More than two years ago in California, a police officer wrote Shaun Malone a ticket for going 62mph in a 45-mph zone. Malone was ordered to pay a $190 fine, but his parents appealed the decision, saying data from a GPS tracking system they installed in his car to monitor his driving proved he was not speeding. What ensued was the longest court battle over a speeding ticket in Sonoma county history. The case also represented the first time anyone locally had tried to beat a ticket using GPS. The teen's GPS pegged the car at 45 mph in virtually the same location. At issue was the distance from the stoplight — site of the first GPS 'ping' that showed Malone stopped — to the second ping 30 seconds later, when he was going 45 mph. Last week, Commissioner Carla Bonilla ruled the GPS data confirmed the prosecution's contention that Malone had to have exceeded the speed limit and would have to pay the $190 fine. 'This case ensures that other law enforcement agencies throughout the state aren't going to have to fight a case like this where GPS is used to cast doubt on radar,' said Sgt. Ken Savano, who oversees the traffic division. However, Commissioner Bonilla noted the accuracy of the GPS system was not challenged by either side in the dispute, but rather they had different interpretations of the data. Bonilla ruled the GPS data confirmed the prosecution's contention that Malone had to have exceeded the speed limit."
Seconded. Furthermore, even if the GPS averaged on a much smaller interval, quoting http://www.pressdemocrat.com/article/20081206/NEWS/812060371/1334/NEWS:
"The distance between the radar reading and when he was recorded going 45 mph is great enough that Malone could have easily slowed down, Heppe testified."
Game over son, you lost.
The problem of this calculus you mention wasnt the speed at the end, nor even the beginning. we're missing a piece of information to properly go through this. distance. it says at a stop light, he was 0, then the next ping was 45. but the problem becomes distance covered in that 30 seconds. tie in the math, etc. if it says 45 on the ping, thats worthless. we need to know how far he traveled in 35 seconds to get an average speed, and, for the sake of argument, his vehicles 0-60 speed as well to get the stats on how quickly he could have possibly gone up to 60, nearly where they "clocked" him. obviously, his average speeds worthless, and his speed 30 seconds after his initial of 0 is worthless. we need the distance traveled in that 30 seconds. And TFA says "virtually" the same location. For all we know, he spotted the cop, hit his brakes and was doing 45 when he was pinged. Distance is key ... notice how TFA forgets that wonderful detail.
And, I'm sure as a teenager, with a GPS, he knew that if he hit 70, theyd get an email alert. Heck, he probably knew that if he wanted to, he could go 69, wait for a ping, if he had timed them right, speed up to 100 and brake to 69 again, all before the second ping... I guess the parents forgot that Teenager + Technology is generally > Parents + technology
The margin of error is for your speedometer, not for you to knowingly drive over the limit.
(tolerance is 3% here in Victoria, Australia);
http://michaelsmith.id.au
"It recorded Malone sitting at a stoplight at Frates Road and 30 seconds later going 45 mph 2,040 feet farther down the road, according to Heppe."
d=rt so we have 2040 = x * 30 so 2040/30 = x x=68!
Yep - GPS proves he was speeding.
No, it does not. GPS only tells you your average speed between two GPS pings. Ping 1 - you are at X, ping 2 - you are at Y, your current speed is how fast you must move in order to get from X to Y in time between ping1 and ping2.
i only caught the part on the pressdemocrat link. missed a whole other link :D
take one thing into account now, the rough 0-60 speed of a car, that can do 0-60 in 6.8 seconds. it would travel around 300 ft if the speed was exactly the same the whole distance to 60. thats the other part we need in this equation and we're golden. if it took him 300 ft to get to 60 at 6.8 seconds. he has 23.2 seconds to continue 1700 ft. so he'd of been doing, 73 :D now figure in his car was really slower then that, but 65 would be about right in the end result. no matter the year of celica, i doubt it was doing 0-60 in 6.8, unless mommy and daddy paid a load of cash to make it go faster... he sped. i think if gps proved he wasnt speeding, it'd of been nice. but they spent all this time fighting a case, where he was speeding anyways. oy vey
Actually, you did your math wrong. 2040 feet / 30 seconds = 46.4 miles per hour.
The thing is, that's the average speed over the 2040 feet. As was mentioned above, given the initial condition of v(0) = 0, this means that at some point in the intervening distance, the kid must have been going significantly more than 45 mph.
The final condition of v(30 seconds) = 45 mph would increase the peak speed even more.
2040 over 30 is 68! I'm sure I'm missing something here.
Yes, he is converting from feet over seconds to mph at the same time.
A GPS typically calculates velocity from Doppler shift of the D-band signal. This give higher accuracy since the position reading is somewhat unreliable. It also means you can (in principle) get the velocity information virtually instantaneously without having to sample two locations. However, in reality a lot of averaging and filtering is going on, and I think many receivers weighs in both position deltas and Doppler shift in the equations, so the reading is going to have at least some lag.
(Reference)
Average speed is easily calculated, based on the statement from this article:
That would be 2040 ft / 30 sec === 0.386 mi / 0.0833 hr = 46.4 MPH
No, but it does provide "related links" to other articles which do provide sufficient detail. He started at 0 MPH, ended at 45 MPH, and averaged 46.4 MPH. That can't be done without exceeding the speed limit of 45 MPH.
"National Security is the chief cause of national insecurity." - Celine's First Law
You're screwing up the part of the Uncertainty principle that most people do. It's not position v. velocity accuracy, but position v momentum. For most large things like planets, cars, insects, and protozoa the mass part of the momentum calculation can drive the accuracy error of measuring both down to about zero. The Uncertainty principle only really matters for really small things like molecules, atoms, and quarks where the mass doesn't overwhelm the equation.
Think about it this way in normal everyday life we're not losing a car because it has a speedometer or the Earth because some one is keeping track of a year. For things like traffic tickets the accuracy of both speed and position are extremely accurate.
Algebra would have done just fine in this case.
The kids dad was the one who fought this the whole time.
The dad got the GPS because of prior infractions by his son.
The kid got 2 other motor-vehicle infractions while this case was proceeding.
Halfway through the case, the dad changed their defense from "The radar gun was wrong", to "It was an illegal speed trap."
They knew they were going to lose the whole time, they just hoped the county wouldn't put out the money.
Example:
They waited until the county had paid the expenses for an expert to come fly cross country and testify. Right before he was to testify, the kids lawyer got a continuation so the expert had to go home and get paid again to come out later.
Correct me if I'm wrong . . .
You are wrong