Elavation accuracy on tracking websites

[SpokeyDokey]

Are any of these three sites generally considered more accurate re elevation accuracy than the others?

Ascent shown for a ride on Wednesday this week over 40 miles:

Garmin Connect 1256'

Strava 1652'

RWGPS 2188'

Quite a variation.

GPS used: Edge 20. I know this is a simple little device but I do not understand how the data is interpreted so differently by the 3 websites. I have a friend with an all singing, all dancing Edge 1000 that gives similar results so I guess the device sophistication makes little difference.

 

[Milkfloat]

Are any of these three sites generally considered more accurate re elevation accuracy than the others?

Ascent shown for a ride on Wednesday this week over 40 miles:

Garmin Connect 1256'

Strava 1652'

RWGPS 2188'

Quite a variation.

GPS used: Edge 20. I know this is a simple little device but I do not understand how the data is interpreted so differently by the 3 websites. I have a friend with an all singing, all dancing Edge 1000 that gives similar results so I guess the device sophistication makes little difference.

Which source do you look at most often - that is the one to use. From a hardware point of view, the Edge 1000 has a barometric altimeter the 20 does not.

 

[Joffey]

Strava runs 'poor data' through their own algorithms (such as Garmin 25) - the Garmin 1000, because it has an altimeter uploads to strava unchanged. As the elevation on your 25 is derived from GPS positions and GPS is poor at judging altitude you get varying results when you upload to the different websites etc.

The above is from DC Rainmaker when he answered my question about elevation discrepancies between devices and websites. He seemed to think you are best off with a device with an altimeter but beware there is a 10% +/- margin of error on them regardless.

 

[NorthernDave]

I've got a Garmin 810 and it can give very variable altitude readings over the same roads. On occasion I've even managed to cycle along at up to 50ft below sea level without getting wet...

 

[Deleted member 1258]

The answer is: Choose one method and stick with it. Ignore the others. It doesn't matter which one you choose.

They're all doing different things. They are all reproducible and consistent, so they are all "right".

They just happen to be a bit different, but so what? If you only use one method, then all your readings will be consistent.

Strava replaces the elevation data from the device by default and uses map elevation data (unless it has a barometric altimeter which I don't think the 20 does). RidewithGPS I think applies a smoothing algorithm to the device's own elevation data, but also provides you with an option to replace the GPX elevation data with map elevation data. I have no idea what Garmin connect does.

Personally I use GPX data from a device with a barometric altimeter (re-calibrated before the ride) and ridewithgps as my own standard for comparing rides. I never look at the elevation from other sites.

No one method will give you a "gold standard" that is better than the others. If you want to get philosophical about it, ask how you would obtain such a "gold standard". You'll find it quite difficult.

Which do you think gets closest, barometric or map elevation ? I know these things are rarely spot on, I just wondered which is likely to get close. personally I don't record every ride, but I do do some using Ride with GPS on my phone.

 

[Deleted member 1258]

Well, this is a difficult question to answer. Because to say something gets closest to the "real" figure you'd have to have some way of measuring the "real" figure. And the answer would change depending on how you did it (do you include every tiny bump in the road etc).

My personal answer to that is not to worry about it.

Map elevation will be more consistent, but will almost certainly under-estimate because the elvation data in the map will be relatively coarse, so you'll have smooth data points. GPS elevation data will be all over the place, because it's a bit crap, so will probably give you a high reading due to jumping around. Barometric data will be subject to shifts in pressure while you ride and anyway isn't all that brilliant.

So I just choose one. I only use it for comparing rides and things like saying "woo hoo, I beat 2,000m" to myself and generally for my own nerdy enjoyment. I don't use it for comparing with anything else. Maybe my 2,000m benchmark is off and it's only "really" 1,500m. It doesn't matter - it's just a number. It's when you try to do comparisons that you come undone. For instance I've seen people on the internet complaining about Strava elevation competitions being won by people using one device or another because it over-estimates. Well ... who cares.

So asking that question is a bit like asking how long is a piece of string.

 

[SpokeyDokey]

I do stick with one (Garmin Connect) which is the low-ball option and tbh I am not bothered as the effort I put in is the same regardless of what the stat's say.

Just interested in the technical reasons behind the massive discrepancies.

As an aside barometric sensors are a waste of space imo - I used to use these when climbing in the mountains years ago and they were notoriously inaccurate due to pressure fluctuations re changing weather. They had to be recalibrated several times on a long climb at known altitudes referenced from maps. I daresay the tech' has changed a bit since then but they are still badly hamstrung esp' over longer rides.

Thanks for the replies.