Well, velocity is a vector quantity which has components of both a speed and direction.
Speed is the rate of change of distance over time.
GPS does, indeed calculate velocity, inherently in knowing the co-ordinates in 3d space at the end of each calculation, the app I use on the phone can then display a velocity as speed and bearing. Note that I didn’t say it underestimated by much but it does assume that you have travelled in a straight line (in 3d space) between the two points used calculate your velocity - since your actual path won’t be a straight line the distance it thinks you have travelled will be less than the actual distance you travelled - hence the displayed speed will be (slightly) lower than your actual speed.
You need to be going round a pretty tight corner for it to make a lot of difference.
"There is a common misconception that speed measured via GPS is done so as a function of position against time. If this were the case, GPS velocity would be just about unusable, because GPS position relies on precise measurements of the distance from the receiver to the satellite, and therefore suffers from numerous effects - such as atmospheric interference - which delays the signal.
Fortunately, velocity isn’t measured like this: instead, the Doppler shift in the signals coming from the satellites is captured and this leads to an incredibly accurate measurement of speed."
Courtesy of Racelogic.
I’m pleased to hear about the accuracy… as I use a GPS speedometer for our classic, as the speedo has gone wrong and we need to dismantle (whatever bits) to send back to UK… drat… no time for that, so GPS helps us out…
That’s interesting. Yes, I confess I did assume that it used the GPS calculated position - the absolute accuracy of GPS positions is 3-5m which is not that great for velocity measurements but the relative accuracy of two close measurements is much better (less than 1m and ISTR recall reading about a project monitoring shifts of a few cm across the San Antonio fault line with paired GPS receivers) and digital filtering techniques can smooth the rest.
Also, intuitively I’d have said “nah” - GPS satellites are in low earth orbit doing about 8700mph relatve to the ground so the vehicle speed is going to get lost in the noise.
But - here is a paper detailing the technique and claiming 0.01kn accuracy - which is pretty impressive.
True about tyres though the GPS is sampling constantly my the metre so I think it’s accurate. I stretched my last Tiguan to a GPS measured 198 kph on an autobahn a couple of years ago. It had absolutely nothing left in it. She’d 170bhp but my current one has 240 so it’s time to try again. I fancy doing 200kph, a speed that was challenging for Porsches and Ferraris only a few years ago, in a little truck.
This is pretty simple really. Since GPS’ measure to three meter accuracy and obviously there’s a location sampling rate then one can work out how far one has travelled between samples, one can also work out what is the maximum deflection one could sustain before disappearing into the Armco or weeds.
Anyway, all real time is an illusion . “One man’s real time is another’s slow motion”.
Actually Paul they terrify me. One can be happily barreling along at 160 thinking your some boyo and what was a tiny spec in yout mirror suddenly comes past you at an outrageous rate of knots. I don’t think I’d like it all the time.
Haven’t driven much in Germany and most of what I did do was around Essen where IIRC there are speed limits but, yes, you really need your wits about you.
Hey hey hey now, I take offense to that. I drive a BMW. I don’t act like a wanker… I even use my indicator (surprisingly enough it didn’t break off after the first few times)…
An old 1970s joke, what is the difference between a BMW and a hedgehog? The pricks are on the inside of a BMW, boom, boom.
Personally I think the 2002 was a great car.
I mean the actual 2002 Ben, the pre 320 model. It was the first BMW that didn’t rust to bits and the 2002 engine was bullet proof. https://en.wikipedia.org/wiki/BMW_M10
Remember the 2002tii and the 2002 turbo? Though the turbo, being the early days, was pretty undrivable due to lag.
. “One man’s real time is another’s slow motion”.
what happens to the vehicles they impound ??
But yes, yes I agree, that does look like a pleasant car to drive 