12:22 p.m. on March 13, 2007 (EDT)
Steve said:
"Some of the cellular phones are advertised as providing GPS location tracking (popular with parents of teenagers that they don't trust, I suppose), but I'm not sure if it's true GPS or just triangulation between cell towers to establish location. If it's true GPS then your location could be identified - but without line of sight to enable communication that wouldn't be worth a lot (since you'd have no way to indicate you need rescue)."
The e911 regulation requires that all cell phone companies be able to provide location, just as your copper-wire phone does. This is so 911 responders can get to the location of the emergency call, even if the caller is unable to speak. The two solutions that cell companies came up with and use are a form of triangulation (too complex to explain here) and readouts of the location from a GPS receiver chipset in cell phone handsets. Most, if not all, cellphone handsets sold since 2005 have the chipset, so that the precise (potentially within 10 feet) location of the handset is included with the digital signature of the handset (the one that provides billing information). Your bill only shows the general neighborhood of the initiating cell tower, but it could show the precise lat/lon.
In short, if you have a recent handset, your location is continuously transmitted as long as the handset is on and is receiving a sufficient signal from the GPS birds (your handset is continuously exchanging information as long as it is on and in range of a cell tower). If you have an older handset, a form of triangulation is used (no, it is not a directional triangulation or resection as you would use with your compass, it works on a different principle, as does the GPS positioning for that matter).
Just as your pocket or vehicle GPSR has canyon and canopy limitations, so does your cell phone. Just having it in your pocket blocks the signals from the SVs, and if your car went off a cliff and into a deep ravine, the GPS signals would be blocked and you are SOL for the 911 guys to recover you (except they might be able to use the cell tower triangulation if you were lucky enough to have line of sight to at least a couple towers so they could narrow things down).
And yes, all cell providers offer tracking handsets that can be queried by parents or caregivers (for Alzheimers patients or special needs kids, for example).
But, no! Your GPS receiver does NOT send signals to the GPS Space Segment or anywhere else. It is a receiver only, just like your Walkman pocket radio. Yes, there are units like Garmin's Rino and emergency service (police, fire, paramedic) radios that include the GPS-derived location in each transmission, and there are tracking units you can place in a car or an ankle bracelet that transmit the location. And the EPIRB and other variations on the locator units that Oregon wants to require do transmit the location when activated (but not otherwise). But your regular eTrex or eXplorist do not transmit any information to anyone. You cannot be tracked through your normal GPSR.
As for using OnStar to issue tickets, this point has been argued for several years now. All cars built in the past few years have a "black box" that stores information on the use of the car, including speed. It is possible to extract that information and use it to issue tickets. Your friendly Mr Goodwrench does that at each service, and the information is used to determine whether you violated the terms of the warranty. But at present, there are no legal standards allowing the issuing of tickets based on that information. There has been a lot of talk about using it for accident analysis, as they do with aircraft black boxes, but so far, no go.