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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.
Yay for GPS technology!
Like anything technological, you have three basic "needs to" requirements:
1. Need to know how to set it up correctly
2. Need to know how to operate it properly
3. Need to independently calibrate it regularly
I have seen a number of cases get overturned here, when the equipment was subsequently found to be inaccurate.
The best (true) story on this subject comes from my days working in Electronic Warfare & Countermeasures.
We made the kit (Sky Shadow) for the Tornado GR4:
http://www.raf.mod.uk/equipment/tornado.cfm
Now, this aircraft is equipped with the ALARM (Air Launched Anti- Radiation Missile ) which works by homing in on enemy ground radar emissions.
So, there were these two local traffic cops with their shiny new radar speed gun, and one of them wondered how fast this Tornado (on a low level live firing exercise) was going........................
Fortunately, the pilot had very quick reactions and aborted the automatic launch..............
:D
So I guess I'd be remiss if I didn't chime in on this one...
RADAR
In my department, all our RADAR units are sent out (to a shop 2 states over) twice annually for calibration. They are only required to be calibrated once a year.
The training for use of RADAR and LIDAR (Light Distancing And Ranging - an IR Laser speed gun) is 40 hours, made up of 16 hours in the classroom with extensive written exams and 24 hours of monitoring traffic with both the RADAR and LIDAR. In order to become certified, you need to show consistently that you can accurately estimate the speed of a moving vehicle within +/- 5 mph. In order to issue a speeding ticket, you need to show that you estimated the vehicles speed at X, which you then confirmed with the RADAR or LIDAR unit to be Y. :ubergun:
GPS
I have no personal experience with Rocky Mountain GPS, but I know that when I'm in the lab, the GPS on my cell phone shows my location to be over .3 miles to the southeast. :rolleyes:
D=R*T
Everybody remember that equation? According to the article, the GPS unit installed in the kid's car transmits data every 30 seconds. So, let's lay it out for worst-case scenario... At a consistent speed of 62 mph, Junior can travel just over 1/2 a mile in that 30 seconds.
Let's say Junior is accelerating from 45 mph to the charged 62 mph. The GPS transmits his location just as he reaches 62 mph. Immediately after hitting this speed, the officer locks on his vehicle and signals him to pull over. If he's only traveled 1/4 of a mile from the time the GPS transmitted to the time he stopped, the GPS will show that he's traveling at 30ish mph. It won't know that he's stopped moving for another 30 seconds.
Now, add in underpasses, tunnels, big rigs, and anything else that might delay the GPS signal and you can cast even more doubt on the accuracy of the GPS. :deal:
Just my $.02 ;)
That is quite hectic.
If we had to argue with the cops here in SA there would be nothing left of us.
Docket lost, case closed. No body :)
Sounds like a Darwin award waiting to happen.Quote:
Originally Posted by nihil