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19 replies

Courses Being Long Even When Measured Correctly

toniyoungmantoniyoungmanMember
I received a call two days ago. A gentleman who measures in South Florida was concerned that our method of measuring with a Jones Counter might need to be called into question. He wanted to hear if I had any insight.

He had preformed a Google Earth Measurement. Then he rode the course, using SPR. The physical measurement came out about 200 feet longer than Google Earth. This is a significant distance. So we talked about his technique. He's been measuring for about 12 years, but only does one or two courses a year. This year he may need to do 8 and wanted to make sure that this measuring wasn't in vane. He had someone run the course, and they complained that it was 400 feet long according to GPS.

My first inclination was to tell him don't worry about the GPS. But I was concerned about Google Earth being that far off. I had him send me the course, and I did my own measurement on Google Earth. It was close, but it was still off by about 150 feet.

Then I remembered an incident from measuring last year. Anyone who knows me, knows I usually measure with a second rider. I measured one course and for some reason the counts were not working out as they should. The second rider had far too many counts at each key point. My first thought was that she wasn't following SPR. Then, since there was more than a 0.0008 difference in our rides, we both rode the course again. Hers were consistent, mine took me even farther. Thank God it was just a 5k in the middle of the summer sun in Florida. At this point, I know something is wrong. When I got home, my husband checked my tires. Sure enough, I had a slow leak. A quick stop to my bike shop for my free tube, and I was off again and my counts looked right.

The gentleman that called me explained that he just put new tires on the bike, he had a new Jones Counter, and his calibration course had been checked by a surveyor with an EDM. I suggested that he might still have a leak, maybe the tube was improperly installed.

He ran an experiment. Using all of his equipment as is, he measured a small course in his neighborhood. He measured it twice, it came out to be within the allowed difference, etc. Then he checked his tube. Yep, you guessed it. There was a leak. He changed the tube, and the distance he measured was significantly longer than the original measurement suggested.

Only through the experiences I have as a measurer am I able to dispense any of this advice. If I measured alone, I don't know that I would have caught the issue last year. I now have a new admirer, but I feel it was dumb luck that led me here.

So my question is this, are there any other things that may make the course measurement do this (go long), if you measure the proper course on the SPR and your Calibration course has not issues?
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duanerussellduanerussellMeasurer
An additional dilemma can be introduced by doing the pre-calibration when the streets are hot, then measuring into a cooling evening, with a slow leak.

Pre-cal will show (for example) 3500 clicks on the cal course. Post-cal may show 3580 clicks on the course. Is this all due to a cooler pavement? A slow leak? Both? Who knows? This is another argument for having pressure gauges on your stems all the time. I know that I can check the pressure, and let some air out at the same time, which gives me a false reading of just-before-checking pressure. (Okay, I don't ever check my pressure, as I ride airless tires.)

I would not be concerned about a 200-ft difference in my measurement and GoogleEarth measurement. I find discrepancies all the time, since the images are rubber-sheeted to make them fit each other. I normally measure an extra 55 feet, or so, on my MapMyRun (same imagery source as GoogleEarth) measurement for a 5k when doing my prep work. Seems to be consistent, most places. Some, however, are further off than that. But, I don't worry about it if all my other indicators are correct.
Last edited by duanerussell
toniyoungmantoniyoungmanMember
Maybe that was what was happening to one of my measurers in New Hampshire. He was consistently getting lower cal numbers with lower temps. Seemed fishy to me. We had a modified Audit done on the 5k course he last measured, and it was found to be 80 feet short. So, in this instance, it did not result in a longer course, but a shorter course. Does that make sense?

The fact that his cals would be one thing in the mid afternoon, and by evening, as the temps lowered, his cals also lowered would have set my spidy senses tingling, had I been measuring. If I saw the pattern continue each time I measured, and I couldn't attribute it to the ground holding much more heat or something else, I would have been checking my equipment.
B bobthurstonMember
Here are a couple more situations where you can create a course that's too long:

1. If rider is pretty wobbly riding the calibration course but very steady riding the race course. (Probably due to wobbly start-up techniques, which affect you more in calibrating than in measuring over an extended distance.)

2. Calibrating on a smooth surface, then measuring on a rough surface. (with pneumatic tires).

I doubt that either of these would create the kind of differences you are talking about, but who knows.

I would disagree slightly with Duane; I think a 200 foot difference between GE and bike measurements would give me pause, as you can generally get way closer than that. (Only if you can accurately see the whole route though.)

Congratulations on catching the leaking tire!
duanerussellduanerussellMeasurer
Bob, after seeing how others, even measurers, map on MapMyRun, I don't think 200 feet is at all odd. What I have to do on the courses I map, and get fairly close to the MMR endpoints, is cut some of the curves inside the curb. I map shorter than what the runner can run and still be on the course. Maybe it is due to elevation changes. Don't know if mapping software includes elevation changes in their calculations.
pastmemberpastmemberMember
Duane refers to the "rubber-sheeting" used in the aerial imagery in on line mapping tools. I don't know how much photomosaicing of the photos may also induce error into on line measurements, but I suspect the distortion is non-trivial, based on my experience attempting to accurately estimate end points of various courses to be measured using these tools.

I suspect that U.S. military-grade remote sensing imagery, software and accuracy standards are far better than the tools available to civilians. To be sure, all of the on line measuring tools commonly available to us employ various algorithms to stitch together images, all of which make certain compromises. These compromises result in warped images which are often visible at highest magnification. I have found that GE and GMaps measurements, done meticulously, result in readings that can be short for one course and long for another, and occasionally, very close to a CBM measurement. I have yet to identify a way to predict the inconsistencies.
oscarwagneroscarwagnerMember
There is a big difference in I see using Map My Run vs either GE or Gmaps Pedometer. GE will get me usually within 10' on a 5K figuring 3.12 to account for the SCPF and tire expansion. I recently measured a half marathon where the director did a MapMyRun measurement of a bike path and was over 1,300' short almost putting a turnaround point in the middle of a 5 lane highway! Worst problem with GE is getting a clear view of the course if imagery was done during "leaf" season.

Oscar
AdminAdminMember
But when you use one of the older satellite images you have to use it for the whole course. The images from different dates are often shifted slightly from each other. So if you draw half your course using the current image, and half of it using an historical image, you'll end up with a path that is not the SPR for the whole course when overlaid over either image.

Because there aren't a lot of winter images available this often results in a tradeoff. Do I use an old grainy leaf-free image or a crystal-clear leafy image?

Man, 10 years ago we would laugh at what we consider problems today!
B bobthurstonMember
I know what you mean, Mark, I'm not quite convinced that you do have to use the other one for the whole course. I think there is a way to test this: place a measuring point at some easy to find point, then switch to the other view and see if it aligns. Many times it will but sometimes there will be the discrepancy you are talking about. I'm interested in hearing if I am right or wrong about this interpretation.

I agree, they don't seem to take those pictures in midwinter. Sometimes very early spring is when I get a good view. But it's all case by case.
B bobthurstonMember
Yes I remember that corner, it was part of Pete's challenge to do a GE measurement of the course that was measured using standard surveying techniques. The same thing happened when I got there, the measurement line was inside the current road. I believe I backed up and used the current picture. Or something.

But I still say this doesn't always happen, it's been rare in my experience. Have you found such "disjunctures" often?
AdminAdminMember
I don't use historical imagery very often, so I don't know. It's not a big problem because it is easy to check. If you use an historical image for one corner make sure to check your path on that image for some other corners where you used the current image to draw it. If your path is off on those other corners then you know the images are shifted and you have to use one or the other for the whole course.
mikewickiser 2mikewickiser 2Member
I have tried MapMyRun and Google Earth in the past. With GE, I have gotten results very near the exact course length on a 5k.
I use GE to work out course adjustments. Getting to within a few feet.
Duane and others have said that MapMyRun can produce equally good results if user properly.
In checking a new Half Marathon course I used MapMyRun and GE to check a proposed route. With Auto-Follow off, I have about a 100 meter difference.
Don't know the actual distance as yet, but both GE & MMR are great improvements over the old days of using dividers and scale maps.
B bobthurstonMember
For what it's worth: years ago the late Norm Brand (he of the "Eye in the sky" entries in the RRTC measuring contests) convinced me that you can get really close to correct measurements by using a good map, a card or paper to make marks on, and good old-fashioned attention to detail. Before GE and gmap-pedometer, etc, I used to measure out possible courses this way. Usually got results within 10 meters or so.

But I agree with Mike, using the computer is a LOT quicker and probably a bit more accurate. The map method does have one advantage: you never have to switch maps because trees are in the way!

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