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Measuring a natural loop course which is almost the exact distance you want

runstephenrunstephenMember
This is my first post on the board. I usually bother Justin Kuo with these types of questions, and he always answers quickly and with detail, but as I may start doing more measurements I don't want to take up so much of his time. Justin, thanks for your help, and you can still answer here if you wish!


I'm going to measure a 5M loop course next week. I've mapped it online and run it with my Garmin 305 and the full loop looks to be about 8070m, +/- 40M. If that holds true the finish will come up just short of the start line. The start/finish is on a straight road which is 300m long and the S/F will be near the middle of that.

I'm trying to figure out ahead of time how to handle contingencies. And there's also a bias by the RD (and myself) toward having the same start/finish line.

If the loop is slightly long, as expected, can I also measure the entire loop? Or is it good enough (identical?) to measure 8047m and then tape measure the distance/gap between S & F, and put that on the map? Is that "gap" certifiable? Can both the 8047m and entire loop distance be certified in one fell swoop as they are so close? Obviously a newbie question.

This may be another way of asking what's best to do to give the RD easiest way to move both lines should he change his mind this year or in the future. Or is this a way to make future recurring income, by charging him an incremental fee when he decides to move it 50m?

What do measurers think about using a 8070m course for a 5M race in order to maintain the same S/F line? As a runner I'm trying to decide what I will think when I race it. The RD would have a certified 5M course (and then some by 23m) and 7 min milers would run 6s slower than they should. Anyone who reviewed the certificate would know they ran extra and could subtract the 6s to get their "real 5M" time for their personal records.

If the LOOP turns out to be 8040m long, how do you note the gap (7m) so that the race director can slide the course in the future? Would/can you note on map/certificate that the Loop is 8,040, or do you instead simply state that the S and F lines are 6.72m apart?

I am thinking about doing a quick extra ride before I do my two measurement rides in order to know the distance within 6m, and be able to answer some of my own questions before starting. Would anyone else spend an extra 25 minutes to do that?

Thanks,
Stephen P

P.S. I already know I tend to overanalyze things, but you can tell me anyway.
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B bobthurstonMember
Stephen,
I suggest that you not think about "what to do if ___" any more until you go out and measure the loop. Try to measure at least 3 times, each time stopping at a set of points you have established. Measure as tightly as you can of course.
Once you've found the length of the loop then you can figure out how to handle this in a race course. Most "natural loop" courses do not come out to a nice desired length, but there are plenty of good ways to handle that.
I'm just afraid too much pre-planning before you have a good loop length might be wasted energy, or worse, might affect how you measure. My 2 cents!
runstephenrunstephenMember
Bob,
Thanks for the feedback.

I *do* already know I have a good loop and I'm very confident I know its length within 0.5% based on my run. Sounds like you are stating that I should consider a 3rd ride to get that to within 0.08% before I do my two measurement rides.

I'm curious so wanted to find out more about the "plenty of good ways to handle" before I started so I can respond to whatever crazy request the RD might ask without having to do yet another measurement on another day. But simply knowing there are plenty is a big plus.
peteriegelpeteriegelRCMBB Founder
If you have already measured the loop twice and have good agreement you have all the measurements you need to certify the loop distance.

If you have a specific course length in mind, you will need to add or subtract length to or from the overall distance to make it come out right, and add split points. Then you will be ready to certify the specific-length course.

As a former runner I don’t think much of the idea of adding length to the course just to make S/F reside in the same spot, unless you tell them what you have done. That’s a deliberate inaccuracy if it’s more than a meter or so.

If any of your estimates of length are based on GPS, disregard them. They don’t have the level of accuracy needed.
runstephenrunstephenMember
Mark, Thanks! Glad to find someone who understands what I'm trying to ask. I know the distance and am wondering what my options are on the mapping step. After I measure next week and know the exact distance I'll still have the same questions originally asked as I discuss options with the RD. Thought I'd get a jump start on that.

Re GPS, yes, at least as accurate as Google Earth, if in the hands of the right person. Of course it doesn't have the accuracy needed for certification, but I can usually estimate a distance within 0.3% using my Garmin 305. Just takes experience and analysis of the results against known benchmarks, such as dozens of certified courses.

I know Justin will help me out with my questions. I'll post the options he offers me in the future so others can learn from them. But still interested in hearing options from anyone who's handled similar circumstances.
peteriegelpeteriegelRCMBB Founder
Anything will do for an estimate. One thing is virtually certain, and pretty well known from previous work. The loop will not come out to an exact standard length. The estimating may yield satisfaction of a sort, but you already have all the information needed to make a decision.

I’ve certified lots of courses like this, and what’s generally done is to make a standard-length certified course by offsetting start and finish. If desired the closed-loop course can also be certified at whatever length it measures out to be.

If it’s very important to have start and finish in the same place one option would be to measure the closed loop and certify it at its measured length. If the difference between the certified length and a standard length is small, the race results can instruct the runners to deduct or add one or two seconds to their recorded finish time. This could offend purists. It might not offend most of the runners, especially if they are told up front how the race will be scored.

Measurement is not the problem here. The problem seems to be that it’s not yet decided how important it is to eliminate the S-F offset.

Without the offset, a standard length will be impossible.

The most useful method for this particular situation would be to lay the course out from mile 5 to start, laying out miles 5,4,3,2,1,0 and loop finish, which will be different from mile zero. I think this would create maximum flexibility for future races,
Last edited by peteriegel

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