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GPS Distance Measuring Devices and Altitude

Submitted by Sibylle on 1 October, 2007 - 12:38
I'd like to pick up the recent debate on the length of the Mountain Highway Madness course.  It's been measured in the past (bike?) at 7.5km to the quarry/15km in total per lap.  At this years running the measurement with a Garmin came up short. 

Our new member Arthur Gee talked to a Garmin rep and emailed me the following:
"I have talked with the rep at Garmin and he states that: There are NO GARMIN products, at the present time, that can give ACCURATE distances with any significant changes in elevation.  He gave as an example, in a 1 mile distance with a 10 degree change in elevation, there will be a shortfall of 150 feet.  GARMIN products are only a 2 dimensional device. Therefore, your 7.5 Km for the Mountain Highway run may be more close to being accurate than it was thought to be on Sunday, Sep 9, 2007. The best way to get an accurate measurement in distance is the use of a mileage wheel."

I find this interesting, as there were a few other events lately were GPS measuring devices surprised us by how short the run was...NOT!  KK now measures pretty much exactly 50km as per Garmin, NOT.  Go Deep measures 20km NOT (I always thought it was a long 20km). 

Not sure how the 10 degree change in elevation measures out in change of altitude over the mile indicated my Garmin.  This will be difficult to translate for the trails of the North Shore Mountains as no trails follows a consistent grade and I would estimate most have a steeper grade than 10 degrees...

Are there any GPS products out there that do take altitude into account?


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ps

Submitted by Dom Repta on 5 October, 2007 - 11:19.
go deep is 20 km to the step!!!!
Sibylle's picture

How did you measure it?

Submitted by Sibylle on 5 October, 2007 - 11:28.
How did you measure it?

GD

Submitted by Dom Repta on 5 October, 2007 - 11:32.
I counted my steps! haha no-I used 2 devices, 1 Nike, one Garmin. It was measured at 19.9 and 20.1. Also, my time hammering as fast as I could indicates the distance. Just under two hours.
Sibylle's picture

Which software did you use

Submitted by Sibylle on 5 October, 2007 - 11:37.

Which software did you use to account for the considerable altitude gain/loss?

 

GD

Submitted by Dom Repta on 5 October, 2007 - 11:44.
I never did-I thought is was pretty flat. What gain/loss.. no software to do that. my own mental software which I think is accurate in distance.
Sibylle's picture

Apparently the Garmin GPS

Submitted by Sibylle on 5 October, 2007 - 11:57.
Apparently the Garmin GPS devices (even the newer ones) do not take the altitude gain into account. In other words, it does not matter to your garmin if you run from point A to point B on a flat course or a mountainous course - your garmin will come up with the same distance - even though you covered more distance on the mountainous course. That's why you apparently need to run your GPS readings through special software that takes the altitude readings into account and translates it...Read, your devices measured around 20km, but in effect it is longer.

I don't care about the exact length of the course. It's good to have an indication, be it the time it took you to run (translates into doubling the time for me ;-) or an approximate distance. Somebody earlier in the discussion pointed out that if anybody wants exact distance they should run on the track - I agree.

What this discussion shows is that even the newer, sophisticated GPS devices don't do our topography on the northshore justice and that at the very least we need to use some software to adjust and even then the numbers are only approximate.

MHM

Submitted by Dom Repta on 5 October, 2007 - 11:17.
I've never thought it was 15 km and my intuition thought it was about 13 and a bit. Andy and I ran down around 20 minutes a couple years back so i knew it was not 7.5 km.
Killaine's picture

elevation crazies

Submitted by Killaine on 3 October, 2007 - 18:35.
I once did a 45 minute track workout, and according to my beloved Garmin 305 I gained 900 m of elevation!
Sibylle's picture

Oh, what a

Submitted by Sibylle on 4 October, 2007 - 07:16.
Oh, what a nuissance...forget these devices!

Rick is trying to find out if his handheld GPS device (also a Garmin, I believe) is taking the altitude into account.
Bill Dagg's picture

Road kill

Submitted by Bill Dagg on 3 October, 2007 - 21:33.
It probably accounted for all of the people you climbed over as you went by.
Bill Dagg's picture

Already discounted

Submitted by Bill Dagg on 2 October, 2007 - 16:05.
Bill Dagg's not concerned. I already discounted my one previous MHM 3-lapper as an ultra and didn't count this year's. It's those guys who start adding distance onto CFA routes thinking that will somehow make them legitimate ultras that need to worry about it.
Ean Jackson's picture

Gimmie a break...

Submitted by Ean Jackson on 4 October, 2007 - 19:18.
I think I'm going to be ill. Taking the moral high road, are we... or just prolonging *your* journey to 100 ultras?
TimWiens's picture

Elevation

Submitted by TimWiens on 2 October, 2007 - 15:09.
I think the GPS results can be fairly accurate if the signal strength was good, there was no loss of signal during the run, and if the elevation profile looks reasonable. I did a lap of MHM on the weekend and got 14.0 km using Sport Tracks. Using Motion Based, which uses different elevation correction software, 13.9 km. The elevation profile looks correct, so I assume the correction for elevation was also correct. I didn't want to mention my results because I know Bill Dagg probably recorded MHM as another ultra, and these numbers indicate something around 42 km :-) If someone knows where I can borrow a wheel, I volunteer to run up old Mt Hwy and and confirm this.
Sibylle's picture

Thanks, Bill and Colin.  I

Submitted by Sibylle on 2 October, 2007 - 10:12.
Thanks, Bill and Colin.  I knew I would elicit some responses with this one.  It's an interesting subject.  I run by time, i.e. turn around at a certain point or by course, i.e. however long it takes to run x loop or from A to B.  Distance doesn't really matter.  However, with the rise of the use of GPS devices like the Garmin, everybody seems to expect accurate distances and I found it interesting that these "raw" measurements are not accurate at all.  Seems like there are ways around with the sofware you mentioned.  I don't own a GPS, so am not familiar with the hoops you have to jump through to get from your "raw" data to something usable.

I have to agree that measuring trails (especially the trails on the North Shore) will probably never be accurate, even if you get close...next year the trail might follow a new turn because of downed trees, a new bridge etc.

Back to the MHM distance...was that "translated"  via software, Rick? 
colinfreeland's picture

GPS Distance Measuring Devices and Altitude

Submitted by colinfreeland on 1 October, 2007 - 21:15.

For the most part a GPS gives you a good estimate of the distance.  This is a two dimenstional distance when the device is recording.  The GPS also record the altitude (however GPS Altitude is not always very accurate) and once this information is uploaded to different programs it make adjustment to the distance.  Different programs make different adjustment.

Here are the distances on my last two runs:

Garmin Forerunner = 4.51

Sporttrack = 4.66

MotionBased = 4.69

Next run

Garmin Forerunner = 9.07

Sporttrack = 9.12

MotionBased = 9.17

Any measurment on a trail is at best an estimate.  Even with the bike computer it is only as good as it is calibrated.  Going up Mountain Hwy it makes a difference if you cut all the corners or take the corners wide, or run on the leftside of the road run or on the right.  The distance is only an estimate.  I would say it is 7.5 km + or - 0.5 km.  If you want exact distances run on the track.

Cheers Colin

Colin (http://colinfreeland/motionbased.com)  (http://colinfreeland/motionbased.com)

Bill Dagg's picture

Un-natural Fixations

Submitted by Bill Dagg on 1 October, 2007 - 21:29.
It's really only important for people with un-natural fixations on ultra counts. :-)
Ean Jackson's picture

Vindicated at last

Submitted by Ean Jackson on 1 October, 2007 - 14:40.
Despite RunRik's assertion ('love 'ya budy!) that MHM is less than 7.5K based on his Garmin results, I'm sticking by my guns:  three (3) laps are an ultra!
Bill Dagg's picture

Talk to Tim

Submitted by Bill Dagg on 1 October, 2007 - 20:56.
You should talk to Tim. I know he downloads his GPSr results into a software program that is supposed to adjust for the discrepancy due to elevation.
Sibylle's picture

How did you measure MHM?

Submitted by Sibylle on 1 October, 2007 - 15:19.
How did you measure the MHM course? Does anybody know the altitude difference from start to turnaround? Can someone find out the average grade if we have the numbers for the altitude difference? 150 feet are only about 50 meters. Assuming about 4.7miles (7.5km) distance and a 10 % grade we only can account for a 235meters discrepancy...Over 30 miles the distance at a 10% grade would translate into 1.5km...
Are the GPS devices useless for measuring distances on the North Shore?

Garmin measurements

Submitted by rune on 7 October, 2007 - 12:41.

For what its worth here is my take on the MHM measurement issues:

* garmins are accurate for measuring altitude - certain models dont but most do

* not sure why garmin rep would say they don't measure elevation.  mine sure does.  i've done numerous mountain summits in kananaskis country and EVERY reading for altitude has been within 50 feet of what the maps from the forest service say.

* if you have done MHM in the past even if the course is short now it should count as an ultra.  It was advertised as 45k and highly unlikely the organizers deliberately made it 42k.  However going forward if it is wheeled and gps'd at 42k and the same course is used it shouldn't be counted as an ultra going forward.

* the newer version of garmin's upload to the unit every 3 seconds so on a gravel road you are not going to lose much distance at all, a winding single track mountain bike trail you will lose a few meters but the course from what i have heard should have no effects on gps measurements provided a signal remains from base to summit.

anyone up for a little easy jaunt on the trails on the shore tomorrow!?

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