# Speed and distance calculations: Do they consider change in altitude?

jimmyfromthepieshop shared this question 19 months ago

Good afternoon all,

This probably won't apply to many people but for certain sports such as skiing where changes in altitude are large it could skew statistics.

So do the calculations for determining speeds and distances take the change in altitude into account?

E.g. If I ski down a hill for 5 km (as seen on a flat map) and descend 1000 m, is my distance travelled shown as 5 km or as slightly longer (5.1 km) because of the drop?

Most of the time this wont be a problem because the discrepancy is so small but if, for example, you want to know your maximum speed down a 40 degree slope then the discrepancy could start to get quite large.

If it is not the case that altitude is considered I won't suggest it as an idea because I understand that discrepancies also work the other way; a calculated distance which is longer than that displayed on a 2D map could also cause problems. I just think it is something good to know that's all!

1

Good day Jimmy,

this is very good question. Currently, all computations in application are based on "flat distance", so change in elevation does not affect distance values.

I can imagine that on longer tracks, mainly with dynamic change of elevation, this may have quite big impact. Elevation measured by GPS is not perfectly stable, so there is a risk, that distance will be in the end a longer then in real.

As I think about it, interesting should be keep current system as is, mainly because of consistency with other tools, not just Locus Map, but also offer something like "Real distance", that should also include elevation change...

Anyway for now, as I wrote above ... "flat distance".

1

If the horizontal distance is 5 km and the vertical distance is 1 km than the distance along the hypotenuse is:

Square Root of 5*5 + 1*1 = 5.099 km.

In other words, the true distance traveled is 99 meters longer. That's not much difference; about 2%.

If you're travelling at a constant 40 km/h it takes 7m 30s to go 5 km.

If it takes you 7m 30s to go 5.099 km, you're moving at a speed of 40.79 km/h. Again, that's not much of a difference.

For the average outdoor sport, the difference between "flat distance" and "real distance" isn't significant.

1

Thanks for the detailed replies, much appreciated and that's cleared that up!!

1

Good day,

i am planning some long distance offroad rally and i am really interested to get real distance data instead of fly path.There is a difference if you are going a 200kilometers a day with 50 meters error. Maybe it would be possible to see two distances when creating new route. Any possibility to show distance by elevation profile not by fly path? And maybe its possible to contact the creator of this software to discuss a bit in private about this function.Thank you

1

Good day,

as wrote in this post earlier, "real distance" is not expected and planned for common usage. The inaccuracy of elevation value is still too high to be used for distance values.

What is your use-case? Do your tracks have elevation values computed from HGT files (by "fill elevation") or measured by GPS? How often you need this value? Last question is because only I can imagine now is another button in "tools" menu of the track (bottom right button) with an option "Compute real distance" that will on request compute this value.

1

Well sir, i need to calculate exact distance on the map. It means when i draw the line, i have to see f.e. 5950 meters of real distance so 3d calculations has to be made before saving the track. Yes, i am using "fill elevation" data. So i came with idea maybe it is possible to show real distance by calculating length of the line of the elevation profile because it draws in real time when i am moving route points around the map. I understand,that elevation calculation will have some errors,but if it is closer to the real distance i rather choose small error than big one. I cant find the solution even using expensive mapping soft. By now locus pro was the best for my personal needs so of course, i would be happy with this update ,if it is possible.The best place would be marked place in attached file. Maybe with possibility to choose between flight and real distance. Thank you

1

Good day,

if you rather choose small error then big, then I really suggest to use current horizontal distance. As I wrote, elevation errors may be really huge and if even expensive mapping softs do not want to risk it, it is another reason for me, not to risk it as well :).

I still do not know the exact reason why you find this value so useful. For me, it looks more like "interesting information" than something that worth extra work (integrating into the whole app may take some time). So what I really can imagine, is really just a button next to "Compute area" in track menu. If there are more people interesting in it, I may do this.