Re: G-Whip Returns

Brian Reay wrote:


The police seem to have commented on the accuracy of the speed from the GPS, which is a legitimate comment. Unless something has changed, GPS units derive speed by comparing changes in position and time- effectively a differentiation (delta position / delta time). I assume you know the problems associated with using differentiation on measurements?

What you are saying here, Brian, is that GPS is not to be trusted for speed.

My last 4 cars have all shown an inaccuracy at all levels of speed according to my very old GPS system. The worst told me that I was driving at 35 MPH when both my GPS and a police speed monitoring trailer said I was doing 29 MPH. This inaccuracy gets worse, the faster you drive. In one car, I could quite happily drive at an indicated speed of 85 MPH and not be bothered by the police. Indeed, I passed one at an indicated speed of 95 MPH and he never batted an eye. (End of shift syndrome? I'll never know)

Dave
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Relevant Pages

  • Re: obeying the speed limit? Pay up anyway.
    ... The father's claim seems to boil down to the fact that the GPS track ... The GPS tracking device that was installed in the kid's car reports ... speeds and positions back to the "main server" at 30-second intervals. ... if the car exceeds 70 MPH. ...
    (rec.autos.driving)
  • Re: fun things to try with your GPS
    ... accelerometer and a wheel speed indicator <non driven wheel>. ... still however profess that 70 mph is absolutely attainible. ... What if the GPS was actually close to accurate? ...
    (rec.skiing.alpine.moderated)
  • Re: Speeding fine couple seek review
    ... actual mph by 3 - 4 mph. ... Are police vehicle odeometers as accurate as mine, ... I done it myself with a GPS. ... I am aware what a GPS is, it's just that I prefer to use maps and not find ...
    (uk.rec.driving)
  • Re: What did they do to my ETec?!?!?!?
    ... I consistently get 200-300 more RPM's and a corresponding increase in GPS ... MPH. ... This is with the boat fully loaded, all equipment, full of fuel, etc.. ...
    (rec.boats)
  • Re: fined for cycling on the pavement
    ... For example a legally compliant car could show 35.5 Mph at a true 30 Mph and 41 Mph at a true 35 Mph. ... Checked against GPS doing a GPS indicated 70mph in a straight line on a motorway my Merc speedometer reads 70mph and my Ford speedometer reads 65mph. ... If you were correct I would expect to see a speed fluctuating on the GPS as different position errors produced positive or negative speed errors. ...
    (uk.rec.cycling)