Jon made possibly his second appearance of the year to lead us on tonight’s run from Beaulieu Road. It was a nice new loop with a mixture of open and woodland. We were once again treated to bright sunshine although there was no breeze this evening which made things a little unpleasant. I’m afraid I wimped out and didn’t do the extra loop down to the south-east at the end. With touch rugby at lunchtime I thought I should be saving myself for tomorrow’s RR10.
Can you explain why the elevation profiles for the two most recent runs show you finishing at a different height from that which you started at? Also, would you not expect all runs from the same car park to start and finish at the same height?!
Can I explain it? At least in general terms… The watch is calculating altitude in the same way that it does horizontal position i.e. based on the location of the satellites currently in view. The best accuracy would be with one satellite directly overhead and at least another three arranged around the horizon but the latter wouldn’t give you particularly good reception! Generally speaking, the margin of error in the vertical direction is about 1.5 times that in the horizontal direction for all GPS. If you want an accurate measurement then you’d be better off with a calibrated altimeter. So, sadly the difference in height at start and finish is just and indication of the inaccuracy.
I do think that in general measuring altitude is fairly difficult to do
accurately and cheaply. For example my watch measures altitude
by using changes in air pressure. Which is fine unless of course the
weather changes more quickly than you change altitude so I still
often find that my start and finish alititudes are different. But it is I
think more accurate than the GPS method.
cheers,
Neil