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#200300 - 03/02/18 05:27 PM How to measure total distance traveled....
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3915
Loc: Ozark Mountains in SW Missouri
I was taking a break today and it occurred to me how I might better explain this concept. Last time I didn't do so well but I think it's worth trying again because, really, how this works is good to know.

For example, on a map the shortest route could look like it's climbing a mountain when really going around it might be shorter and faster, and easier.




You can find more info on this here.

I expect a few of you are laughing away right now (at least I hope so). laugh


Edited by billstephenson (03/02/18 05:28 PM)
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#200304 - 03/02/18 10:07 PM Re: How to measure total distance traveled.... [Re: billstephenson]
Glenn Roberts Online   content
Moderator

Registered: 12/23/08
Posts: 1550
Loc: Southwest Ohio
Your idea of “taking a break” is a WHO-O-O-O-LE lot different than mine! smile

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#200314 - 03/03/18 10:19 AM Re: How to measure total distance traveled.... [Re: Glenn Roberts]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6560
Loc: Gateway to Columbia Gorge
Mine, too! lol
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#200317 - 03/03/18 04:52 PM Re: How to measure total distance traveled.... [Re: OregonMouse]
wandering_daisy Offline
member

Registered: 01/11/06
Posts: 2797
Loc: California
He let you off easy! Could have given the geometry fromula to calculate total distance from elevatin gain and map distance.

In reality, our hiking paths are usually lower angle than the drawing. Even what we think is steep uphill is usually under 20 degrees, so the actual distance is not off as much as the drawing implies.

Off subject, but, I just discovered the "health" program on my I-phone (OK, I am late to figure this out). It gives steps and distances. I find this is quite a bit off at times. It seems to significantly over-estimate distance just puttering around, and slightly underestimate distance on a real long-stride walk. On one of my dog walks that I have determined as 4.5 miles on a real GPS, it gives me anywhere from 3.5 to 3.4 miles. I just got back from afternoon grocery shopping and it said 1.0 miles (no way!). Supposedly it uses a combination of steps and GPS tracking to get those numbers. Since I live in flat-land, the diagram above does not apply.

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#200318 - 03/03/18 04:54 PM Re: How to measure total distance traveled.... [Re: wandering_daisy]
wandering_daisy Offline
member

Registered: 01/11/06
Posts: 2797
Loc: California
Oops! meant 3.5 to 4.4 miles.

Anyone know exactly how the I-phone calculates distance?

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#200320 - 03/03/18 08:00 PM Re: How to measure total distance traveled.... [Re: wandering_daisy]
Glenn Roberts Online   content
Moderator

Registered: 12/23/08
Posts: 1550
Loc: Southwest Ohio
There’s a formula?!

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#200321 - 03/03/18 08:07 PM Re: How to measure total distance traveled.... [Re: Glenn Roberts]
balzaccom Offline
member

Registered: 04/06/09
Posts: 1800
Loc: Napa, CA
Bill, most GPS units measure elevation as well as distance. Not sure why you think they don't. In fact, twenty years ago the GPS unit for my boat always asked me to confirm my elevation before zeroing out the unit to make sure it was being accurate.
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#200326 - 03/04/18 02:17 AM Re: How to measure total distance traveled.... [Re: balzaccom]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3915
Loc: Ozark Mountains in SW Missouri
A "GPS" will not add elevation gain/loss to your total distance traveled. That's a pretty common misconception and why I pointed it out here.

Estimates of satellite heights can be off a lot so you just can't use those to determine your elevation. Some GPS units have a built-in altimeter that increases accuracy but those readings can lose accuracy if a weather front changes the atmospheric pressure quickly.

And elevation gain/loss measurements are given separately so you have do the math yourself to calculate that part of the equation.
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#200330 - 03/05/18 03:12 AM Re: How to measure total distance traveled.... [Re: wandering_daisy]
JustWalking Online   content
member

Registered: 01/12/16
Posts: 185
Loc: PNW
Not positive, but I think the iPhone, on its own, uses its three-axis (3D) accelerometer chip to calculate steps/distance (unless a separate program is used that takes advantage of the GPS). An article I read says that "as you walk, the accelerations can be used to compute both the number of steps, and - separately, the distance you travelled. So it is acceleration and a little math, that is how distance is measured."

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#200335 - 03/05/18 12:23 PM Re: How to measure total distance traveled.... [Re: JustWalking]
wandering_daisy Offline
member

Registered: 01/11/06
Posts: 2797
Loc: California
Thanks for that information. Sounds reasonable, but like you said, never know for sure with Apple's secrecy on a lot of its functions.

I do not care about steps; only distsnce. I was wondering if after doing a long-stride outdoor walk, when I come inside, and just putter around the house, the GPS may not be able to pick up all that small movement, so wondered if my actual step is then sensed, and the distance is extrapolated from that. Half mile to a mile just around my house seems grossly over-estimated. Or perhaps, the GPS itself cannot accurately detect distance on small back and forth movements.

I did a 6-mile walk yesterday, that I have previously traced on an actual Garmin GPS, and it was spot on with the I-phone.

Another factor may be that cell coverage is spotty (never get more than 2 bars) so perhaps parts of my walks are not recoreded at all.

Just saying that if you plan to use your I-phone for distance on actualy backpacks, be careful!

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#200337 - 03/05/18 01:29 PM Re: How to measure total distance traveled.... [Re: JustWalking]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3915
Loc: Ozark Mountains in SW Missouri
I'll have to look into that. I've played a bit with an accelerometer connected to a Raspberry Pi and that's some truly amazing tech.

What I used is small pc board that's about a 1" square and has a magnetometer and an accelerometer on it. I hooked it up to a Raspberry Pi computer and made an animated compass. I made a video of it and blabber on a bit about how I hacked it together and posted it on YouTube.

I didn't try to measure distance with it though. I didn't even know that was possible but those Apple engineers are a lot smarter than me laugh.

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#200339 - 03/06/18 10:29 AM Re: How to measure total distance traveled.... [Re: billstephenson]
HPD Offline
member

Registered: 12/22/16
Posts: 64
Loc: Colorado High Plains
Appreciate the diagram Bill, but I think it gave me a flashback headache!

I find the Apple step/distance/flights recorder not all that accurate also. I started using an app called ViewRanger. It works pretty well for distance/elevation gain & loss and tracking. It seems to work without cell service but works best if you download maps of the area you're going to, beforehand.
Worked great for me last year coming down off a mountain and keeping me close to the route I took up. App is or was free, map downloading cost about $15 for a lifetime subscription. The key is keeping your phone charged, which I'm working on.

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#200340 - 03/06/18 07:58 PM Re: How to measure total distance traveled.... [Re: HPD]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3915
Loc: Ozark Mountains in SW Missouri
I bring both my iphone and a garmin gps, and keep the phone off to save battery life, so I've never compared how the two match up. It'd be interesting to do that.

I don't have many apps on my phone though, and seldom use it. I do like having it when I'm backpacking though. There's not too many place you can't get a signal here anymore so it's pretty sweet to have along.
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