GPS vs Radar

[cmr164]

Nabbed for speeding? GPS data could get you off the hook

By Jacqui Cheng | Published: July 18, 2008 - 11:57AM CT

As anyone who has ever gotten a speeding ticket knows (full disclosure: I never have... knock on wood), you often have very little ammo to fight back against the reading that the all-knowing radar gun spat out. But thanks to more sophisticated and affordable technology, that could be changing. GPS data was able to get a California teen off the hook for allegedly going 17 miles per hour over the speed limit, simultaneously casting doubt on the accuracy of police radars and giving hope to tech-savvy drivers.

[willbird]

Nabbed for speeding? GPS data could get you off the hook

By Jacqui Cheng | Published: July 18, 2008 - 11:57AM CT

As anyone who has ever gotten a speeding ticket knows (full disclosure: I never have... knock on wood), you often have very little ammo to fight back against the reading that the all-knowing radar gun spat out. But thanks to more sophisticated and affordable technology, that could be changing. GPS data was able to get a California teen off the hook for allegedly going 17 miles per hour over the speed limit, simultaneously casting doubt on the accuracy of police radars and giving hope to tech-savvy drivers.

Hey it might help keep everybody honest :-)

[Fuzz]

I have read several threads here and other stories about similar issues. The problem I have is that the GPS system (even in this article) says it only takes a reading once every 30 seconds. THAT IS NOT AN ACCURATE SYSTEM. Many of the defenses use the theory that at one reading the violator was at point A and 30 seconds later the violator was at point B so they show that the distance between point A and B would have been greater if the violator was actually going the speed they were cited for. The problem with this is that people do not always go the exact same speed. The violators speed could have changes several times in a 30 second window. If they were going 60 mph for 15 seconds and then 35 mph for 15 seconds the average speed that the GPS would calculate based on the 30 second delay between readings would be much lower than the violators highest speed. If the officer catches the violator as they have just sped up the GPS will show a "history" of a lower average speed, but if the violator had just sped up within the last 30 seconds the GPS would not have taken a new reading yet.

[mk70ss]

My problem with that defense is this; I need to bring certification of our LIDAR/RADAR units calibration to court to prove their accuracy. Who proves the GPS is accurate in their defense? But the courts here in Mass ALWAYS favor the defendant, NEVER law enforcement.

[willbird]

I have read several threads here and other stories about similar issues. The problem I have is that the GPS system (even in this article) says it only takes a reading once every 30 seconds. THAT IS NOT AN ACCURATE SYSTEM. Many of the defenses use the theory that at one reading the violator was at point A and 30 seconds later the violator was at point B so they show that the distance between point A and B would have been greater if the violator was actually going the speed they were cited for. The problem with this is that people do not always go the exact same speed. The violators speed could have changes several times in a 30 second window. If they were going 60 mph for 15 seconds and then 35 mph for 15 seconds the average speed that the GPS would calculate based on the 30 second delay between readings would be much lower than the violators highest speed. If the officer catches the violator as they have just sped up the GPS will show a "history" of a lower average speed, but if the violator had just sped up within the last 30 seconds the GPS would not have taken a new reading yet.

I know both my gps units will show a SPEED change far more often than 30 seconds.

Bill

[Freddie]

HEY SPEEDERS LOOK!!!!!!

Oh wait, this would only work if you weren't speeding. I guess you're still screwed then.

[Monkeybomb]

GPS is not an accurate gauge of speed. It does not read on a consistent enough basis to put a particular speed with a particular location at a given time. Unless you have a military system. Our PC's have an MDC with an AVL and it is accurate at times. Other times it is way off. I mean blocks off and reads my speed very low in traffic with stoplights because it is an average. Alot of the accuracy from gps depends on how many satelites it is tracking at one time. 13 very accurate. 3 is ballpark. The other for a moving object is how many times it calculates that position. I looked at the story about the kid winning the case and the court was nice to him but it wasn't proof of anything except that he was there......... Nice try though saved him a little cash.

[PB3021]

My problem with that defense is this; I need to bring certification of our LIDAR/RADAR units calibration to court to prove their accuracy. Who proves the GPS is accurate in their defense? But the courts here in Mass ALWAYS favor the defendant, NEVER law enforcement.

What he said....

[PB3021]

Except for the M******* part.

[SgtCHP]

Shaun was found guilty of speeding in a trial-by-affidavit thanks to a report from an expert saying that the GPS data could not have been accurate.

Ah, good ol' Dr. Heppe stood up against the giant GPS manufacturer. Ah, but did he?

the same GPS expert was called to testify. Dr. Stephen Heppe ended up backtracking on his original report, however, once he was on the stand. Rocky Mountain Tracking says that Heppe "corrected" his original statements and painted the device as being quite accurate after all, "to within a couple of meters on location and to within 1mph on speed."

Nope! The GPS group got to him, probably made it worth his time and Dr. Heppe modified his opinion. So, the judge, enamored with the good doctor's credentials and idiotic testimony, reversed his decision. I believe he also testifed that GPS gives an instantaneous report on speed instead of having to measure distance to get the speed. Everyone knows that you cannot get a speed reading instantaneously, for goodness sake, speed is evaluated by the time it takes an object to travel between two points. But, the judge forgot that small issue of fact.

But, as HotHardware points out, that same data could eventually be used against you, too. All the police have to do is obtain subpoena for your GPS data when you argue that you weren't really lead-footing it down a straight stretch of the highway a couple of weeks ago..

And, so it continues, there is a hearing schedule for October 3rd, where the great city of Petaluma has hired its own GPS expert: "...A GPS expert the city retained has been called to testify twice, at $5,000 per appearance, and is scheduled to return Oct. 3 when the trial resumes."

I can't wait for this one to go to the 9th Circus Court of Clowns!

[GGG]

I know both my gps units will show a SPEED change far more often than 30 seconds.

Bill

Sure, you get a readout constantly, but your GPS is not logging every millisecond worth of data. The memory would quickly fill up. It takes readings every 30secs (or whatever the manufacturer set it for) and logs that data.

The other problem with GPS data is that there are times when the unit gets a false reading for location, then gets the correct reading a second later. So if it gets a false reading and thinks you are 150ft from where you really are, then gets the correct reading 1 second later. It will think you travelled that 150 feet in that 1 second, so it will show your speed as 102mph. So when the GPS data is subpeoned, you might find yourself much worse off than the original ticket. I had a GPS that had recorded a max speed of 600mph+. My BMW is not that fast.