[dsn_klr650] nklr: gps vs bicycle computer mileage

[Dreas Nielsen]

Oh, right: 0.19%. That's what I get for picking up the calculator before the coffee cup in the morning. But as for relative vs. absolute error, if the GPS has an absolute error of about 0.1 mph, then the relative error in the (computed) distance traveled will certainly be different if your speed is .1 mph, say, than if it is 60 mph. However, because the fundamental measurement made by the GPS is distance (well, position) rather than speed, and it is the distance measurement (made over a one-second interval) that actually has an absolute error, then the calculated speeds have a different relative error if you travel 1.5 feet or 88 feet in the one second between the position measurements used to calculate distance. And as for the point of my original post, it certainly wasn't to make invidious comparisons between the precision of the BC and GPS. Dreas

> -----Original Message----- > From: Steve Anderson [mailto:standerson@...] > Sent: Tuesday, August 01, 2000 7:13 AM > To: DSN_klr650@egroups.com > Subject: [DSN_klr650] Re: NKLR: GPS vs bicycle computer mileage > > > Dreas, > > I think you missed a decimal point there my friend. 0.11 / 58 = > 0.001897... > = ~0.19% > > But you missed the point. It is NOT a relative error, it is an absolute > error, that is independent of speed. > > > I doubt your bicycle computer can come even close to this error, whether > measured relative or absolute at 58mph. Maybe you have a really > good one;-] > > > And if you want to look at the relative error anyway, why not > compare it to > the appropriate frame of reference: > > Your speed relative to the satellites is well over 1000mph. > > 0.11 / 1000 = 0.00011 = .011% ; pretty darn good!! > > > Steve (been around a few blocks with GPS) Anderson > > > > --- In DSN_klr650@egroups.com, "Dreas Nielsen" wrote: > > > --- In DSN_klr650@egroups.com, "Dreas Nielsen" wrote: > > > > > > > > > > I don't know the relative precision of the GPS's distance > > > > measurements (neither the Garmin manual nor Web site provides this > > > > information) (and it's probably speed-dependent), but I'd be > > > > surprised if it was much better than a couple of percent. > > > > > > > > Dreas > > > > > > > > Garmin specifies the speed of the GPSIII(and +) at 0.1 knot, > pretty darn > > > good. The errors in the GPS come from the fact that most of the units > we > > use update > > > once per second, and compute speed in terms of the straight > line between > > the > > > two points, even though in a turn you travel a larger distance. > > > > > > Steve A. > > > > An error of 0.1 knot (or 0.11 mph) at 58 mph, the average > rolling speed I > > made on my trip, is equivalent to 1.9 percent, which I > certainly consider > to > > be not much better than a couple of percent. I don't mean to argue that > > that is not pretty darn good, but that it indicates that the > correspondence > > between the BC and GPS was markedly better than expected. > > > > Dreas > > > > > Visit the KLR650 archives at > http://www.listquest.com/lq/search.html?ln=klr650 > Support Dual Sport News... dsneditor@... > Let's keep this list SPAM free! > > Visit our site at http://www.egroups.com/group/DSN_klr650 > To unsubscribe from this group, send an email to: > DSN_klr650-unsubscribe@egroups.com > >