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GPS Discussion

What does RaceMeasure offer you, the racer/runner?  Besides listing as many certified races in the U.S. that we can find (go to the Search page);

RaceMeasure certifies courses to USA Track & Field standards, assuring you that a course has been measured accurately, and that split locations are located accurately.  We supply a detailed map to the Race Director, so they can lay out the course properly on race-day.

Runners

Q: What’s wrong with this picture?

A: They don’t have their bib numbers
on the front!

You can see the certification map for any course we have listed (we measured many of the Colorado listings, and other USATF measurers measured the rest), so you can preview the course, if you would like.  And, on race-day, unless there were last-minute changes (required by weather, or construction, etc.), you will know where the course is supposed to go.  If the course changes and we don’t have a new map posted (check our site the day before your race to make sure nothing has changed), the course is not certified, and you should run the course as marked, accepting the inaccuracy.  There may be a safety reason to follow the course as marked, so please, even if it is wrong, follow the course markings. In most cases, if the race is a “qualifier” for another race (Boston Marathon, Bolder Boulder, for instance), the deviation will be measured, and times will be adjusted accordingly, thereby allowing the race to remain a “qualifier”.

“The course is not the right length”. 

We hear that from some runners who wear a GPS device during the race.  GPS devices are not precise!

SEND ME YOUR GPX FILE! (GPX is a universal GPS format) I want to analyze the files from the GPS device that you wore. WIthout analysis, there is no basis for claiming the course was too long. Send it to info@RaceMeasure.com

If there were trees over part of the course, or the race ran between tall buildings, the GPS could have lost contact with the satellites, and the recorded distance is not accurate. Or, due to the curves in the course, runners may not always follow the shortest possible route.  This adds distance to your GPS reading.  Race courses are measured using the shortest possible route that a runner may follow and still stay on the race course. You may not have been able to run the shortest route, due to other runners being in your way. There are many reasons not to rely on a GPS for an accurate course measurement, and each situation will have different reasons for that particular inaccuracy.

Recently I went out and ran with a GPS in each hand. One was a Garmin eTrex Legend HCx (high-resolution antenna), the other an Oregon 450 (also a high-res antenna). I only had time for a two-mile run, but it was very revealing.

I started both units tracking from a cleared track log at the same spot. I was standing still, and reset each simulaneously. I then began running. The eTrex was always in my left hand, the Oregon in my right. Both were held with the antenna facing the sky, as directed. The course had some trees along it, but I ran on the sidewalk by the street, at least 30 feet away from houses at all times. I also ran around a park, with a clear view of the sky.

When I finished, I stopped, and turned both tracks off at the same time.

When I downloaded them, and looked at the tracks and reports, the eTrex said I had run 10487 feet, or 1.99 miles. The Oregon reported 10581 feet, or 2.00 miles. A difference of 94 feet, or .8%.

What this shows is, GPS devices are not precise. I didn’t try to run the Shortest Possible Route, as courses are measured, as it was irrelevant in this test. But, if you run a race, and your unit is off by 94 feet before taking into consideration following the shortest route, your measurement of the course could be off by over 150 feet, very easily on a 5k course. Keep that in mind if your GPS doesn’t show your race to be the length you thought it should be.

Follow this link for visual examples of GPS inaccuracy.

There are many reasons why certified courses don’t match less-precise measurements.  For a more in-depth presentation, please go to Colorado Runner Magazine or Dave McGillivary’s discussion.

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