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Picture of Pete Riegel
posted
Lee Barrett writes

I know the issue of GPS wearing runners complaining of long courses had been much discussed in the past, and the issue came up again this year after the Portland Marathon. There were several postings on the marathon's Facebook page about the course being long. I did respond to the person who started the postings, sending a copy of the Stuart Gordon article and their response was, "5-year old technology". It seems there is nothing I can say to satisfy these people that the course
length is accurate.

After discussing this with the marathon technical staff we have come up with a plan. I will ride the course, more like a runner would, that is not cutting every tangent and riding as if I'm certifying the course.
On my bike I will have a Jones counter, a smart phone running Map My Ride, and a Garmin GPS watch. It will be interesting to compare the
three devices recording distances over the same course at the same time.

Any thoughts or suggestions?

Lee
 
Posts: 1747 | Location: Columbus, Ohio, USA | Registered: 23 October 2004Reply With QuoteReport This Post
Picture of Pete Riegel
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Mike Sandford provided a nice group comparison of 26 runners using their electronic gizmos in a half marathon.

Group Comparison

The people doing the complaining are true believers in the accuracy of their units. I doubt we will succeed in changing their minds.

"A man convinced against his will
is of the same opinion still."

"My mind's made up. Don't confuse me with facts."

This message has been edited. Last edited by: Pete Riegel,
 
Posts: 1747 | Location: Columbus, Ohio, USA | Registered: 23 October 2004Reply With QuoteReport This Post
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Pete,comparing the Jones counter to a Garmin Forerunner 305 on the Portland Marathon route.

I've just returned from measuring the marathon course, riding the route more as a runner would than as I would when certifying the course. I cut some tangents but not all of them. I used a Jones counter and also carried a Garmin Forerunner 305 watch. Pre ride calibration of the Jones counter on a 1/2 mile course showed an average count of 15356. Start counts 634000, finish counts 1037512 (I DID NOT use the short course prevention factor), so total distance traveled was 26.277 miles. Post calibration average was 15350. The Garmin 305 recorded 26.35 miles. The Garmin was 0.08 miles longer than the Jones counter. Both measurement devices covered the same route at the same time. Actually I was hoping that the Garmin and Jones would be closer, but that was not what my data shows, I wonder why this is the case. So I can only conclude that not only does the Gramin measure longer than the Jones counter, but runners wearing them are not taking the shortest possible route which compounds the error.
 
Posts: 19 | Registered: 13 October 2007Reply With QuoteReport This Post
Picture of Pete Riegel
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I’ve played with Lee’s data and here are some observations:

Certified true length of the course = 42237 meters.

Lee’s measured length “as runners would run” using average constant = 42297.3 meters


Garmin measured length = 42406.2 meters

Number of turns on course = 36 as I counted from the certification map.

Sum of degrees of all turns = 3070 degrees = 8.85 complete circles.

If a runner ran 1 meter outside the SPR on all turns, this adds 53.6 meters to the course. Total distance run would be 42292 meters.

2 meters outside SPR = 42344 meters
3 meters outside SPR = 42398
4 meters outside SPR = 42452

From above I figure that Garmin users ran about 3 meters outside the SPR on turns, or about 10 feet out.

Lee’s measurement looks like the line he took was about 1 meter beyond the SPR. Maybe so, maybe no.

This is pretty speculative, but it does provide agreement between Garmin and the certified length.

I looked at the site for the Garmin Forerunner 305 but did not find any claims for accuracy
 
Posts: 1747 | Location: Columbus, Ohio, USA | Registered: 23 October 2004Reply With QuoteReport This Post
Picture of Mark Neal
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This comes out to a difference of 0.25% between the Jones and Garmin measurements, and agrees well with the numerous tests that I have performed and also the ones that Mike and Gene have done.
When care is taken so the same path is followed for the Jones and Garmin measurements, the difference between the two is almost always less than 0.4%, and often a lot less.
 
Posts: 938 | Location: Rochester, MI | Registered: 13 April 2006Reply With QuoteReport This Post
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