Short GPS reported measurements

Mark, never had a complaint that the course was short. Of course there was quite a tiff a few years ago on Facebook when the Portland Marathon changed its course and all the GPS folks thought is was long. I tried to explain the measurement process but they did not want to hear it. One of their closing statements was, "so I guess we're all wrong". Unfortunately for them they were!

Lee Barrett

I used to mount a Garmin GPS on my handlebar when measuring, just as an additional check of distances. However, I stopped carrying it after I noticed it would occasionally show the distance traveled as shorter than what I'd actually measured. I discovered that it would sometimes loose satellite contact and later pick it up again.

I believe that when it did that, it treated the distance between loosing and regaining satellite contact as a straight line, which was always shorter than the distance that I rode. For somebody using a GPS during a race, this would certainly report the course as being too long.

Good observation Mark!

I have only heard a “short course” GPS concern expressed one time. Every other challenge was due to the GPS “seeing” a long course.

The one short was easy to explain. That 10K (NY09062JG) has a lot of tree cover forming a thick canopy over much of the course plus there are signal blocking ravines. Ron is correct. The GPS unit must assume a straight line had been traveled during the outage when the signal is reacquired and the GPS wearer is further down the road.

While measuring that 10K my GPS once reported a sudden elevation jump of 100 feet! Not in reality of coarse, just on the GPS screen. That’s very disappointing. I was hoping the GPS was magic.

Sometimes the GPS wearers are helpful. I was alarmed after a race on one of my 5Ks earlier this year. Many GPS wearers reported 1/10 mile long course! Some were mad! Signal reception should be excellent over that entire route. Fearing the worst, I rushed out to see what might have gone wrong with my measurement.

Nothing. The course (NY11029JG) was still well marked and not physically altered. Everything checked out fine. The map couldn’t have been clearer. But the GPS should not be THAT wrong with all this open sky and a small race such that the GPS runners should not have been that far off the shortest possible route.

Fortunately, the event had captured promotional video of the race. We studied it… It clearly showed that the race had permitted a sub-contractor (the timer) to inexplicably set up the finish line exactly 1/10 mile further down the road. The GPS wearers were RIGHT! The course they ran was 1/10th mile too long.

I was glad I had held my tongue and not given the "GPS Geeks" my technology lecture before learning what actually had happened...

JJ

Jeff,
I think you might be surprised at how far off most people will run from the SPR, even in small races. Now that I am old and slow I end up in the middle of the pack in the rare race that I run. I have noticed that people tend to just follow the people in front of them. If a person runs next to the left edge of the road around a right-hand turn, everyone behind will follow. I think people do this partly because they don't pay that much attention, but also because taking a shorter route than the person in front of you would feel like cheating.

Mark,
I agree, I have seen some whoppers as far as making good choices in where to run. There's another thing-- runners like to expand to fill up whatever road width is available, whether or not they're getting a distance advantage.
At the Army 10-miler a couple years ago we had a situation where the middle of 3 lanes was blocked due to construction but the outer 2 lanes were open. I made a project of trying to encourage runners to go into the left side as well as the right because, considering the entire set of curves they were heading into, both sides were about equal in length. I must report that my efforts were next to useless. From their point of view it looked shorter to go to the right side, and besides the people in front seemed to go to the right side. At that point folks could not see that 300 yards ahead there was a huge traffic jam of runners on that side and I began to feel like the King of England in the story (King Canute?) who tried to command the seas not to rise any farther.
Here's part of what happened in that race: frustrated runners, slowed to a walk in the lane they had chosen, just broke right into the middle lane, hopping over rebars, dodging around backhoes, and somehow surviving this adventure (at least no reports of hospital trips by any runners).
The one exception to the pattern of not following spr too closely is this: on occasions where I've acted as lead biker, elite runners notice right away that I'm showing them a good route to run and they buy it immediately. Maybe an argument for that blue line like they've used in London and other places.