You are hereForums / Preparation / Geek Gear (GPS/Comps/Lights/etc.) / Motionbased Elevation inaccuracy
Motionbased Elevation inaccuracy
Dirtworks 100km 2950m elevation gain??? On the day my Garmin gave an elevation gain of under 2000 m (Polar 710 reading 1815m). Have a look at http://trail.motionbased.com/trail/activity/8150081
Anybody else experience these huge anomalies with motionbased?
- Login to post comments
- Bookmark & share
We might have spoken about this before? Or perhaps it was in an email conversation?
Anyhow - there are several methods of working with the elevation data that comes out of these devices.
You can add/subtract every little bump. I don't think anyone does that.
Or you can add only when the elevation moves more than a certain amount (say 25cm).
Eg, device says 1000.00m -> 1000.20m -> 1000.10m -> 1001.00m.
Note that some devices will do this even though they are only rated to 1m accuracy. Also note that with GPS only elevation will be hopeless. Even with barometric altimeter you can get discrepancies based on weather over long rides or when a strong weather front comes through.
Anyhow, using absolute method you'd get 0.2m + -0.1m + 0.9m = 1.1m total rise, 0.1m descent.
Using 25cm smoothing you'd get 1m rise only.
I think MB uses smoothing somewhere around the 25cm area because I've written some similar S/W and it gives similar readings with that setting.
This overrides the evelavtion calculations recorded in your Garmin Edge and uses elevations calculated from Motionbased's world map which is way less accurate and is designed for devices that dont have inbuilt barametric altimeters. If you check my ride profile the elevation gain / loss was 2,045m using the barometric altimeter. Also as Rob posted there are calculation differences between different software that also makes a difference to total elevation.
http://trail.motionbased.com/trail/activity/8134375