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

jimmyfromthepieshop shared this question 2 months ago
Answered

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!

Thanks in advance for your response!

Comments (3)

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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".

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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.

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