Fun with GPS

In true press release style, let me state my conclusions first and then give you the evidence. This minimises the chance of missing out on something because of tl;dr.

  1. Endomondo is an unreliable measurer of distance and altitude, and if you want accuracy rather than encouragement, ViewRanger is better on a phone.
  2. GPS altitude sensing on a phone gets very unreliable at speed. If you want an accurate picture of a cycle ride, use a dedicated GPS device

So, here is my evidence:

Having done much walking over the last months, I have been struck by the fact that on my phone, Endomondo consistently overstates the distance walked, compared with ViewRanger — by as much as 10 percent. In order to find out which was more trustworthy, I staged the following experiment.

I ventured out for a recreational bike ride today(first for two months — idleness and concentration on walking are my excuses) and tracked my route with three different GPS apps on two different devices. I have a Garmin Edge satnav for the bike; and I used Endomondo and ViewRanger on my phone. The results are quite interesting.

  • Garmin said I did exactly 27 miles, with a height gain of 988 feet and a max altitude of 564 feet (expending 1699 calories)
  • ViewRanger said I did 27.2 miles with a height gain of 1066 feet and a max altitude of 559 feet
  • Endomondo said I did 27.3 miles with a height gain of 2913 feet! and a max altitude of 741 feet (expending 1850 calories)

So, although on this occasion, Endomondo didn’t much overstate the overall distance, it got any attempt at recording altitude completely wrong — Picture 3 below. (Endomondo’s only advantage is that you don’t have to pay for the maps.)

I also noticed that the variability of the altitude in ViewRanger was most marked in the parts of the ride where I was going faster. In the crawl up to Newlands corner, the altitude reported was close to the map altitude. Elsewhere, there was considerable variability between what the (OS) map stated and the GPS reading recorded. (First picture below). On a walk, the correspondence between map and GPS is very close (2nd picture below).

I also include the Elevation profile as captured by the Garmin and Endomondo as the most and least accurate versions.

All utterly pointless, but I enjoyed conducting the experiment :-)

Today’s cycle ride — height profile according to ViewRanger
A typical walk profile screenshot from ViewRanger
Garmin Edge version of the top picture
Endomondo getting it completely wrong
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