Author Topic: Difference in altitude is not correct  (Read 248 times)

Offline helkenner@gmail.com

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Difference in altitude is not correct
« on: August 08, 2021, 18:52:45 »
I use the planner on the homepage and notice that the altitude information is not correct. They are to high compared to my Gps device and e.g. the page "Brouter-Web". (Example 65 km cycle tour: Locus 845 hm, Brouter 632 hm, Gps device 610 hm).  The distances in kilometres are nearly accurate. Only the displayed altitude gain (German: "Höhenmetergewinn") is not correct.
Is there an explanation for this. Which elevation model does locus planner use?
 

Offline poutnikl

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Re: Difference in altitude is not correct
« Reply #1 on: August 08, 2021, 20:04:17 »
I guess you do not mean altitude itself, but the total altitude ascend, which is computed from the recorded altitude profile or from SRTM data for planned route

Estimation of the true altitude ascend is tricky. There is no a priori way to determine the just proper level of filtering. It is always balancing of filter oversmoothing of real details with leaving residual altitude noise due GPS or SRTM artefacts.

It is quite common Locus planner comes with up to twice value, compared to Brouter value based on used built-in filtering.

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Offline tapio

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Re: Difference in altitude is not correct
« Reply #2 on: August 09, 2021, 07:16:23 »
Here's a good reading about elevation gain calculation which lets us understand why a) it is not trivial and b) why different services deliver different values.
https://www.gpsvisualizer.com/tutorials/elevation_gain.html

Best way as a user is to use a consistent data source, consistent usage of flattening/correction... same software when comparing elev. gain.
« Last Edit: August 09, 2021, 07:32:09 by tapio »
 
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