Comments on: Odometer versus GPS http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/ The MTBGuru weblog and forums Wed, 25 Jan 2012 22:41:08 +0000 hourly 1 http://wordpress.org/?v=3.0 By: AChang’s BLog » Hello world! http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/comment-page-1/#comment-67 AChang’s BLog » Hello world! Tue, 23 Jan 2007 19:22:04 +0000 http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/#comment-67 [...] The slope of this curve is of course the speed, and you can quickly identify the descents, climbs and breaks. Distance is calculated from latitude and longitude using the great circle distance formula as mentioned in another post. [...] [...] The slope of this curve is of course the speed, and you can quickly identify the descents, climbs and breaks. Distance is calculated from latitude and longitude using the great circle distance formula as mentioned in another post. [...]

]]> By: mtbguru http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/comment-page-1/#comment-25 mtbguru Sat, 30 Dec 2006 21:56:08 +0000 http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/#comment-25 @ragetty; What I wanted to claim is that the GPS data will converge with the 'real' distance traveled (as measured by the wheel sensor) if its sampling speed would be increased. I agree with you that the fact that the wheel sensor measures the real distance is not due to sampling speed - as you say, that's true because the wheel tracks the features of the trail. So I probably should rewrite the last paragraph ("this is so because the odometer simply...") because that says indeed something different than what I wanted to say ;) @ragetty;
What I wanted to claim is that the GPS data will converge with the ‘real’ distance traveled (as measured by the wheel sensor) if its sampling speed would be increased.

I agree with you that the fact that the wheel sensor measures the real distance is not due to sampling speed – as you say, that’s true because the wheel tracks the features of the trail.

So I probably should rewrite the last paragraph (“this is so because the odometer simply…”) because that says indeed something different than what I wanted to say ;)

]]> By: ragetty http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/comment-page-1/#comment-24 ragetty Fri, 29 Dec 2006 14:38:01 +0000 http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/#comment-24 i don't think this has anything to do with sample frequency, rather that the wheel follows the contour of the ground (with it's subtle or not so subtle highs and hollows) and not a straight line (or arc of a great circle) between any two points. the wheel (more) accurately integrates all lengths travelled by the wheel over all inclinations, whilst gps calculates the distance between 2 points assuming they are at the same elevation (i.e. the surface of a smooth great sphere otherwise known as earth). no matter how often the gps sampled, it would still be in error due to method of calculation - e.g. for a continuous and smooth 10% slope, this is 50cm every 100m, if also undulating then even higher. if the wheel sensor was constructed to record only every 10 revolutions, you can not convince me that the tacho would now show less distance travelled - this would have to mean that the wheel slipped *backwards* somewhere. i don’t think this has anything to do with sample frequency, rather that the wheel follows the contour of the ground (with it’s subtle or not so subtle highs and hollows) and not a straight line (or arc of a great circle) between any two points.

the wheel (more) accurately integrates all lengths travelled by the wheel over all inclinations, whilst gps calculates the distance between 2 points assuming they are at the same elevation (i.e. the surface of a smooth great sphere otherwise known as earth). no matter how often the gps sampled, it would still be in error due to method of calculation – e.g. for a continuous and smooth 10% slope, this is 50cm every 100m, if also undulating then even higher.

if the wheel sensor was constructed to record only every 10 revolutions, you can not convince me that the tacho would now show less distance travelled – this would have to mean that the wheel slipped *backwards* somewhere.

]]> By: mtbguru http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/comment-page-1/#comment-10 mtbguru Sun, 24 Dec 2006 09:36:24 +0000 http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/#comment-10 Yes indeed. To be clear: this article compares data taken on a bike ride from a GPS to data from an odometer/cyclometer (device based on a sensor counting wheel revolutions). Yes indeed. To be clear: this article compares data taken on a bike ride from a GPS to data from an odometer/cyclometer (device based on a sensor counting wheel revolutions).

]]> By: BayAreaBiker2001 http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/comment-page-1/#comment-9 BayAreaBiker2001 Sat, 23 Dec 2006 22:15:15 +0000 http://blog.mtbguru.com/2006/12/23/odometer-versus-gps/#comment-9 A GPS can swithc from biking to running/hiking without modification. A cylometer is limited to biking, a pedometer is limited to running and walking. A GPS can swithc from biking to running/hiking without modification. A cylometer is limited to biking, a pedometer is limited to running and walking.

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