FR: real distance calculation using elevation data

[sikmir]

On mountainous tracks, the difference between flat and real (including ups and downs) distance can be significant.

[tumic0]

Do you have a real example of such a track? Because on all tracks I have seen, the difference is usually smaller than the GPS inaccuracy... Maybe in case of a flight the difference may be relevant, but even then I would still prefer to measure the "flat" distance as this is IMHO the expected value of the distance in that case.

[sikmir]

Do you have a real example of such a track?

Let's look at some track on GPSies: Fann Mountains.
Flat distance:

Real distance (calculated by GPSies):

I guess GPSies uses DEM data. Using GPS recorded elevation it should differ even more.

I would still prefer to measure the "flat" distance as this is IMHO the expected value of the distance in that case.

Sure, "real" distance is not a replacement for "flat" one, but just an additional metric.

[tumic0]

Ok, it could be added to the statistics window. But I don't want to "mess" the GUI with this value on any other place or even implement some switch logic, as the usage of this value is IMHO marginal.

[jdehaan]

One example of tool showing the "real distance" is http://utrack.crempa.net/. On one of my tracks I had a 18,8km vs 20,7km.

[tumic0]

If I'm counting correctly, this is more than 8500m elevation on the ~20km track which is quiet unusual. However it is still only ~10% difference in distance which may easily equal to the GPS measurement error. And on usual tracks the percentage is much lower.

I do not dispute that this may be a usable feature for some people, but things that would need to change are not that trivial like it may seem (the elevation and distance are quiet separated in the code at the moment). And for me and my tracks (my measurement errors) this has almost no added value, that's why I let it open, but with a very low priority...

[jdehaan]

Ok I understand your point. On most city tracks this feature would be quite useless but I am living near to many hills and my tracks are full with ups and downs :-). Thanks for your nice software. If I can find some spare time I could try to provide a PR to implement this somehow. Unfortunately with family it's not so easy for me to find time. Cheers!