Distance measured on incline by GPS

[neilmny]

A question was asked by a friend the other day regarding what a GPS measures distance wise.
My assumption is that it triangulates distance traveled on the earths surface by using horizontal distance and altitude change.
Is this correct?

A small doubt arises in my mind from looking at my track profiles in Mapsource.
The scale at the bottom of this view appears linear (not variable) and appears to be horizontal distance only.
This would mean I'm walking a lot further on hills than I think I am if this is the case and no wonder I get tired legs

[Tyreless]

I don't know the answer but the difference isn't as great as first thought. An example I read: climbing Howitt Spur from Howqua River to peak of Mt Howitt - 5000m horizontal and 800m vertical. Assuming it's a triangle then the distance (hypotenuse) is 5,064m, only 64m longer. But try telling your legs that.....

[michael_p]

GPSr record waypoint to waypoint distances in 2D. They do not measure distance in 3D. Also worth noting is that the vertical error in your GPSr can be 5x the horizontal. Most GPSr have a 3m horizontal error which means that the vertical error can be 15m (and that's on a good day).

So, yes. You may be walking further than you think if you are walking up long and steep climbs.

This information packed site is old but still very relevant: http://www.gpsinformation.net/

Cheers,
Michael.

[neilmny]

Thanks Michael.
I'm always walking in steep country with long steep hills carrying a pack to keep fit.
Walking further than I think I am is a good thing

[GregR]

I don't know the answer but the difference isn't as great as first thought. An example I read: climbing Howitt Spur from Howqua River to peak of Mt Howitt - 5000m horizontal and 800m vertical. Assuming it's a triangle then the distance (hypotenuse) is 5,064m, only 64m longer. But try telling your legs that.....

I've never thought of like that, the maths hold up- interesting indeed. I'll give my legs a stern talking to tonight.

[neilmny]

I don't know the answer but the difference isn't as great as first thought. An example I read: climbing Howitt Spur from Howqua River to peak of Mt Howitt - 5000m horizontal and 800m vertical. Assuming it's a triangle then the distance (hypotenuse) is 5,064m, only 64m longer. But try telling your legs that.....

Wow I missed yours Tyreless as I just had a quick squizz while I was working. Not much to get excited about there is there.
It is likely not really a triangle as there will be more ups and downs in real life but the error is likely to be a small percentage and distance more than expected in training terms.
We can't be bragging about powering up a near vertical cliff for blah blah kilometres when we actually did less

I suppose when it's all said and done the slopes we walk are not much more than say 30 percent. A lot I walk are around 23 or so percent and they are hard yakka.
I saw someone write of a hands and knees vertical cliff that he had to "walk" (perhaps negotiate is a better description) carrying a heavy pack.
It was probably only 45 around degrees (50%) which is very hard to get traction on by foot in my experience, even on a good surface.

Last edited by neilmny on Tue 28 Feb, 2017 3:37 pm, edited 1 time in total.

[scroggin]

Tyreless is right.
It can be misleading looking at mapsource where the X axis scale values can be multiple times that of the Y axis. Mind you that 1:1 gradient in mapsource is how I remember it as oppose to the 10:1 gradient it actually was.

[neilmny]

Tyreless is right.
It can be misleading looking at mapsource where the X axis scale values can be multiple times that of the Y axis. Mind you that 1:1 gradient in mapsource is how I remember it as oppose to the 10:1 gradient it actually was.

You can make yourself feel mighty good by compressing the X scale and extending the Y scale though scroggin

[madmacca]

I don't know the answer but the difference isn't as great as first thought. An example I read: climbing Howitt Spur from Howqua River to peak of Mt Howitt - 5000m horizontal and 800m vertical. Assuming it's a triangle then the distance (hypotenuse) is 5,064m, only 64m longer. But try telling your legs that.....

Hi Tyreless. This is your legs answering. Each 1% of incline represents about 10% more effort. Walking up a 10% incline is about double the effort of walking the same pace on the flats.