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Old March 12th 19, 01:04 PM posted to rec.bicycles.tech
Rolf Mantel[_2_]
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Posts: 267
Default GPS Units = Show road steepness?

Am 10.03.2019 um 23:36 schrieb :

For every position on earth the altitude is known (measured during a
Space shuttle mission if I recall correctly). The information is
available for free.


The information is available but not in the necessary precision for road
gradients; uploading GPS tracks to Strava it is usually most meaningful
to replace the GPS altitude by 'true altitude' but look at the results:

https://www.strava.com/activities/1206896182

The first km, I am faster in the evening than in the morning so I assume
it's level or extremely slightly uphill, Strava thinks it's losing some
5m within 1 km.
Around km 1, there is a steep drop by 2m, followed by a climb of 2m
which is not visible at all in the track.

From km 6 to km 8 the track has a constant "climb" of 1m; Strava
interpolates a peak of 15m altitude into that which is not there in
reality.

Almost everything is correct to within a few m; the map-based
information produces a lot less spurious altitude gain and loss than the
GPS based information but this is not good enough for comparison of
gradients unless you're talking hills with 20m altitude gain or more.

I speculate my trip to work is 10m - 20m altitude gain in total on 11k
distance, the map brings it to 40m, GPS measurement typically around 60m.

Rolf
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