Terrapin Tables

What really freaks me out in that article is the possibility that the speed of my car could be regulated. If that happens, how am I supposed to outrun the police after I steal the TV?

Okay, this makes no sense to me whatsoever. The television, stereo, etc will be inside, not necessarily within view of at least two GPS satellites, which is required for a fix. If the criminal who steals your TV is smart enough to obstruct the antenna, the police won't even get a fix when he takes it out of your house. As for their claims of 1 meter accuracy, total horseshit, not possible with commercial GPS. Once again, inaccuracy of the GPS fix would make the car speed tracking function very problematic, if not damn near impossible. This guy is seriously smoking crack.

Yeah, you can't get 1 meter accuracy, but you can get under 10 meters with receivers now, which is close enough to find a burglar's address. And by using a form of GPS that uses specially built towers on the ground, you can get under 5 meters, and gain the ability to judge speed. The Acme car rental agency has already done this, and then fined their customers for speeding after they returned the vehicle. But then they got sued and lost. In any event, I've heard about the government tracking vehicles -- it almost certainly will not happen, especially not in the U.S. And yeah, you can wrap tin foil around some receivers, and then they won't work.

Can't they give you a ticket on the Jersey Turnpike if you go between two EZ Pass points too quickly? Seems pretty close to this Acme car rental thing. Just curious...

You're right Rick, it is possible to get within five meters with Differential GPS (D-GPS), but as you said, it requires specially built towers which are actually rather expensive to construct. My point was, this scientist first of all believed that one meter accuracy was necessary and/or desirable for this application, which as you pointed out is not the case. Regarding vehicle-tracking in general, remember, OnStar is becoming more popular, and more and more cellphones have GPS installed. The government isn't leading the effort to track people, people are.

Yeah, if they wanted, they could certainly give out tickets by going through EZ Pass points fast enough. I'm sure NJ could make a ton of money one weekend if they really needed to. Not the best PR of course, but they'd still get a decent amount of revenue from a lot of people who don't live in the state. Also, m math teacher in high school said that whevenever someone challenges tickets like these (saying he never got caught doing a certain speed), they have to bring up the fundamental theorem of calculus to prove that at one point the person had to have been going over the limit.

Update:Most of you should be able to go back and edit posts/comments now. No more of that pesky proofreading required. Lord knows I don't.

Well, in a related subject look at the new OBD III standard (or this link, at the bottom) being developed for cars. The current standard, OBD II (on board diagnostics) is incorporated on every new car sold in the U.S. It monitors just about everything your car does so the computer can control emissions, and as a bonus side effect, can also be used by mechanics to aid in diagnosis. Well, the plan is for OBD III equipped cars not to use the cable that is currently required for mechanics to connect to the car, but to be wireless. Which means that your car could tell a roadside station if your having emissions problems, what your speed is, or any number of the parameters that the car's computer monitors. Civil liberties groups will probably keep it from becoming too bad, but the potential's there.

Oh, and as far as GPS giving accurate speed, I though it could do that without a perfectly accurate position, because I thought the error was consistent. I know GPS is now accurate enough that it's used for precision instrument approaches for aircraft, so it's got to be pretty good. And I thought the government got rid of that intended error in the commercial signal. Did they put it back in?

The intentional error put in by the government (Selective Availability) was taken out in May 2001, and hasn't been put in. Most likely never will be put back in since it stayed off during 9/11.

First I heard about ODB III being wireless. A lot of nice uses, but yeah, open for abuse. I wonder how they'll handle proprietary ODB's like the one in my car.

Update: Heh. I wrote ODB instead of OBD. Dirtydirtydirty. Okay, I'm done. This thread is long enough.

It's not a rapper- it's OBD, not ODB. Anyway, proprietary stuff is in addition to EPA required stuff, so it's up to the manufacturer to decide how they want to do it. Maybe still with a cable, maybe with a separate code sent to it to make it output the proprietary stuff.

Yep Rick, you nailed the SA point. The error that's left is atmospheric, the signal from the satellite is delayed due to refraction, which isn't consistent, and thereby reduces accuracy. Now, by convolving the positions given over time it is possible to correct for the atmospheric error, but it won't be too useful in the context of finding your TV.