These are the results I get using the code I'm running. Distance and Elevation are both converted to feet:

Quote:

Leg 1 - Distance : 10.3625268966932 ::: Elevation : 3.14960630400012 Leg 2 - Distance : 26.9923527802663 ::: Elevation : 12.6312336149999 Leg 3 - Distance : 18.9807255710197 ::: Elevation : 4.72440945599999 Leg 4 - Distance : 4.40460389188256 ::: Elevation : 1.57480315199987

Total Distance : 60.7402091398617 || Elevation Change : 22.0800525269999

That should give you the numbers you need to run your math and compare to the total distance shown. You should probably double check my numbers, but you only need to check two legs of data to confirm if they are good or not, and I'll fix them if they are bad.

I would run that last bit of math myself, but you'll have to explain what "delta_x^2" means. Is there a way to write that in longhand math that I can better understand?

Hopefully you'll forgive me for not being able to decipher the formula you've offered. I never had an opportunity to take any math classes past the eighth grade, schools in LA were pretty overcrowded in the `70s...

Edited by billstephenson (02/17/1203:09 PM) Edit Reason: clarification

Registered: 03/14/11
Posts: 66
Loc: SF bay area, CA

I'm not too familiar with perl, but it seems like it should be able to handle these operations. A quick search shows me that exponents (that I write with a caret) use double asterisks **, so the length of leg 1 would be

or in numbers ( 10.3625268966932**2 + 3.14960630400012**2 )**(1/2) = 10.8306

and then add all the lengths together to get

10.8306 + 29.8016 + 19.5599 + 4.67766 = 64.8697

Sorry if my abbreviations for square and square-root aren't familiar; I spend my days staring at equations and tend to forget that most people don't. Let me know if that doesn't help any!

Registered: 02/07/07
Posts: 3625
Loc: Ozark Mountains in SW Missouri

Originally Posted By: squark

and then add all the lengths together to get

10.8306 + 29.8016 + 19.5599 + 4.67766 = 64.8697

That worked!

Here's what I got:

Flat Distance : 60.7402091398617 Adjusted for Terrain Distance : 64.8697213477516

That's a big difference for just 60 ft of travel, and that sample was taken from my GPS track of a hike in the hollow below my house. I did grab that small piece because it had a notable variation in elevation, so it's not an average sample, but what it shows is significant.

If anyone has a track they'd like to run through the code I'd be glad to post the results. For that matter, if anyone wants the code, I'd be glad to send it to you.

Ummm - clearly the unit of measure used will determine the actual distance traveled. This is where CHAOS enters into the equation. Its like how many miles long is the west British coast? Now using a mm long measuring device and going around every rock and nuance, how long is it? The answer approaches infinity as the unit of measure shrinks.

A gps adds the horizontal distance between the points where it takes a data sample. If it is set to sample every minute and you meander, the distance covered will be less than if it samples every half minute, etc.

Of course the GPS will say the two waypoints are .87 miles apart. If you really did travel in a straight line up hill at 30 degrees, it would say .87 miles on its odometer - the sum of the horizontal distances between the data points. Jim

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Registered: 02/07/07
Posts: 3625
Loc: Ozark Mountains in SW Missouri

Quote:

Ummm - clearly the unit of measure used will determine the actual distance traveled.

Yep, a GPS set on it's finest grain of data collection points does not provide a very high resolution picture of what you actually hiked, and the way your milage is calculated by a GPS ignores terrain all together.

There is solid logic behind that approach and your "This is where CHAOS enters into the equation" observation is the root of it.

That logic applies best to things like maps and boats and airplanes, and works just fine for cars on roads, but it's not so good for hikers that want to know how far they actually hiked. So the little app we are working on goes as far as possible with the data available from a GPS to give a better estimate of actual boots on the ground miles.

Still, compared to the most accurate piece of technology we currently have for measuring that, the best GPS still sucks.

Registered: 02/07/07
Posts: 3625
Loc: Ozark Mountains in SW Missouri

Originally Posted By: wandering_daisy

There may be some GPS units that have a chip inside that converts, thus allowing you to choose how you want distance presented. I suspect most do not simply because there appear to be many different ways to calculation depending what you want to measure. Anyway Gershon needs to look in his manual and see if there is a setting that allows one or the other.

I'm not aware of one that does that, but companies like Garmin are pretty responsive to users, and if one requested a "Miles Hiked" feature that accounted for elevation I'm pretty sure they'd add it. If they added it to their "BaseCamp" software it'd be free and backwards compatible with their hardware, and it'd be a feature that'd hit their target market for that product.

On their hardware, they could add it with a software update, and if they kept only a running total they could obtain a much finer degree of accuracy while using little processing power or storage space.