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Ralsina.Me — Roberto Alsina's website

Endomondo Lied To Me

A week ago I re-s­tart­ed my di­et and ex­er­cise plan. Since I am gross­ly over­weight, the ex­er­cise plan is ba­si­cal­ly "walk around 5km ev­ery day, fat guy". Since I am a nerd, I want­ed da­ta so I could stop ly­ing to my­self about how much I was walk­ing.

I had seen En­domon­do men­tioned in my tweet­er time­line a bunch of times and the fea­ture­set looked pret­ty much ex­act­ly as I need­ed:

  • Track my walk­ing

  • Keep his­­to­ry

  • Show it in google maps (be­­cause it's nice)

It even did things like track­ing calo­ries burnt and so on.

The on­ly prob­lem was... it re­al­ly sucks at fig­ur­ing out how much you walked. It con­sis­tent­ly over­es­ti­mates by around 50% the dis­tances, and since it cal­cu­lates the av­er­age speed based on time and dis­tance (and the time mea­sure­ment is cor­rec­t) it over­es­ti­mates speed by 50%, which then means it over­es­ti­mates calo­ries burnt by (I am guess­ing) 125%.

How did I ver­i­fy that En­domon­do is wrong, and avoid the ob­vi­ous ex­pla­na­tion of "y­our GPS is bro­ken"?

  1. I tracked my­­self us­ing En­­domon­­do and Google Trails at the same time.

  2. I coun­t­ed steps ro­­man-mile style (count ev­ery "left­­-right", mul­ti­­ply by 1.6)

  3. I mea­­sured the path I walked in Google Maps and Bing Maps

All those mea­sure­ments tell me a walk of 1100m +/- 150m is mea­sured by En­domon­do as 1.68 km

Ver mapa más grande

Why does this hap­pen? I could as­sume En­domon­do is just crap, and prob­a­bly be right, but try­ing to come up with a "in­ter­est­ing" ex­pla­na­tion, I am lean­ing to­wards noisy mea­sure­ments. For ex­am­ple, if En­domon­do saw my po­si­tion shift­ing ran­dom­ly 10 or 15 me­ters left or right it would prob­a­bly add enough noise to make the path 50% longer (for a much more fun ex­am­ple of this, read this pa­per (by no oth­er than Benoit Man­del­brot!) but this does­n't ex­plain why Google Trails works so much bet­ter (un­less Trails does some­thing smart with an­tialias­ing and in­ter­po­la­tion).

If you use En­domon­do, care to share your ex­pe­ri­ence? I am re­luc­tant to 1-s­tar it in Google Play with­out in­de­pen­dent con­fir­ma­tion.

cHagHi / 2013-05-16 00:13:

I've been using Endomondo to track my running sessions for (I think) more than a year, and I'm not seeing this behaviour. I always run more or less the same "circuits", and I have tracked those circuits with other tools (My Tracks, Sports Tracker) in the past, or have measured them in Google Maps, so I know Endomondo has not been that wrong. Endomondo estimates also match the length of some "well known" circuits (f.i., the Reserva Ecológica Costanera Sur in Buenos Aires has a bunch of different paths, and the lengths of those are documented elsewhere). Also, I have used Endomondo to track some street races in which I have participated, and the distance reported by the app was consistent with the distance of the circuit prepared by the organizers of those races.
So... Endomondo never lied to me, at least not in such a noticeable way ;-)
One interesting difference between our use cases is that you used the app to track walking, while I have been using it to track running.

Martín Volpe / 2013-05-16 00:47:

I've been using CardioTrainer for a while. It has all the features you mentioned and I can tell, It works just fine!

Fernando Perez / 2013-05-16 02:25:

This could just be a units issue: 1.1 miles is close to 1.68km. It's perfectly possible that the code got a unit conversion wrong, and multiplied from miles to km when it shouldn't.

Run another test, and if the error is always a factor of ~ 1.6x, then the most likely explanation is this.

Manuel Muradas / 2013-05-16 02:34:

"Google Trails" == "Google Tracks"? Vengo usando el segundo para caminatas, bicicleteadas y patinadas, y la verdad que está muy bueno.

Podés subir los tracks a Google Drive y guardarlos para la posteridad, para cuando les contemos a nuestros nietos que antes podiamos caminar 5km =)

Siempre me quedó la duda si la velocidad que mide es real. Tendría que compararlo contra un Garmin a ver cuanto delta hay.