Why Garmin records less elevation gain!

I record my bike rides on Garmin Vivoactive and then sync it with my Strava account. I notice that I normally get anywhere up to 40% less number than my fellow cyclists who record rides on Strava Mobile App. I posted this to couple of forums on WhatsApp, Facebook and went through some blogs, other online content. But nothing was conclusive. So I decided to do my own research.

 To get the elevation profile a device has to keep recording elevation data at frequent intervals. There are two important things to do this.
  • Accuracy of the elevation data each time it is recorded
  • How many data (stamping of GPS & Elevation) is taken/stamped for a particular distance
Accuracy of the elevation data

 There are two way elevation data is captured by devices.
  • GPS Positioning
GPS Positioning also has elevation data tagged. So with attitude and longitude devices also get elevation data
  • Barometer
Some devices and some phones have Barometer. Barometer can measure atmospheric pressure and as we all know atmospheric pressure depends on elevation at any given point. So based on the atmospheric pressure the elevation data can be correlated and found.

 It is said that Barometer based measurement is little more accurate than the GPS coordinate based measurement of elevation. However difference is not much it is not reason why I get such low elevation gained number when I record on my Garmin Vivoactive. 

 How many data (stamping of GPS & Elevation) is taken/stamped for a particular distance

I looked at the GPX files of one of my 105 KM ride which was done on an off beat route. I got elevation gain of 1037m and my friend who recorded in Strava Mobile app got elevation gain of 1755m. What I found was astonishing. Strava Mobile app had stamped 16282 (approx) time the GPS coordinates and elevation whereas Garmin Vivoactive had stamped only 2183 times. Its a huge difference. And this is why the difference in elevation gained stats. Less number of data per meter will mean less accurate elevation profile recreation. And hence the difference.

 Here is plot of the two elevation profile. Although it is difficult to make out anything from this but if you run elevation gained analysis on the two profiles you will know the difference.

So it is fair to say that Strava Mobile App will be more accurate than Garmin Vivoactive. 

Why does Garmin stamps less number of times? My guess is to save on battery (it has much smaller battery than a mobile phone) and to use less memory (Memory also is much smaller than mobile phone). 

Again, if you check same stat for a 100 km route which frequented by cyclists (like a standard practice route). The difference in elevation gained between the two methods is not much. 

Why? Again my guess is that Strava does some elevation correction based on all the data they have from various rides. If this is correct then I'm impressed with all that Strava engineers are doing. Still would want Strava to bring back Google Maps though!


Disclaimer: The above is my own analysis and I'm happy to take comments and revise this blog if proven wrong. Please leave a comment if you feel you have a valid point.


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