Measuring the Equinox Marathon

I'll give you my opinion, and others will tell you theirs. Filter all of our responses to what best fits your course.

From your description (root-filled trails, which indicates there are trees overhead), there is no one ideal way. If you use a Jones on a mountain bike, you have wobble going up technical hills, which introduces some inaccuracy.

If you use multiple GPS units, then average the results, you still have interference from trees (I don't know what kind of GPS coverage you get up there, but if there are less than 8 birds visible, accuracy diminishes, regardless of trees or other interference).

A wheel takes too long, and is inconsistent in its contact with the ground.

None is ideal, but if you could ride a mountain bike with two GPS units on the handlebars, you would then have three measurements. Look at the GPS tracks in the GPS software on your computer, and adjust (where you can) where one deviates off the course, if the other seems to follow what the true course is. Compare the corrected course lengths with the Jones counter, and you should be pretty close.

You will not be able to certify, since there is lots of undulating single-track, but you should have a fairly accurate measurement, with splits in the correct spots.

That's how I'd do it, if it were my course.

Thanks for the reply and the suggestions. The issue many have with GPS measurement is that it doesn't take into account the undulations and is measures distance as essentially a flat course. Do you have an opinion on what kind of hit the accuracy takes with so much undulation and elevation change?

Back to basics.

I'd be inclined to measure it with a steel tape. I'd only do it once and forget about certification.

I'd figure it to be a two day job.

A three-person team would make things relatively easy.

I think your best bet would be a GPS. But when you take the measurement use the distance the GPS tells you directly. Don't download the track and use Google Earth or something else to tell you how long the track is. Even at their highest resolution settings GPS units save a smaller number of track points than they use internally to calculate the distance.

The added distance due to elevation changes is almost always trivial. Your course would have to have a constant grade of 5% for the error due to elevation change to be about the SCPF, or 0.1%. A constant 5% grade is a monster course. It's unlikely your course, even if it's a trail course, is this hilly.

The armchair approach would be the easiest. If the route can be followed on Google Earth the horizontal length is easily obtained.

As Mark says, the elevation will likely make little difference. However, if, as you are mouse-measuring on Google Earth, you record the elevations (at bottom of screen) as you go, you can correct for elevation. You will have a series of straight-line measurements, each bracketed by an elevation.

Geometry will do the rest.

This is likely bad advice, as I'd be surprised if the route is easily determined using Google Earth.

How about posting before the race:

The course does not lend itself to dead accurate measurement. Over the years the distance has become accepted as the about standard marathon distance.

Although personal GPS devices will have some error, we will record, post-race, as many readings as can be gotten from the year’s participants and publish those results.

One careful GPS measurement you take yourself will be much more accurate than averaging the GPS measurements of race participants. Some of them will start their GPS watches when the gun goes off rather than when they cross the start line, some of them will go off the trail to relieve themselves, and none of them will run the SPR.

I will take issue with Pete's assertion regarding the accuracy of a Google Earth measurement (I usually agree with Pete, but not always).

When I measure ANY course, I always do a very careful mapping in MapMyRun. All online programs use the GoogleEarth underlay, I believe, so they all measure the same. But, I always map it out 2/100 of a mile long, whether a 5k course, or a marathon course. (My marathons map to 26.24 or 26.25 miles.) That usually yields a mapped course that measures with a Jones to be the desired length.

Satellite imagery is rubber-sheeted to make the edges and corners of different images match. If you happen to be in an area where many images were distorted to make them fit, your online measurement could be very different than an on-the-ground measurement. That's why I don't trust online measurement for precision. But, this may be your best method, if you allow for the rubber-sheet variance.

I'm with Pete, for what it's worth this issue will never be out to rest until the accuracy over the root section can be positively verified, steel tape will do it.

Ride to a spot before the root section, if possible triangulate the stopping point, measure from there over the root section via steel tape to another stopping point past a root section (also triangulated) and back to bike.

Those points can be documented and referenced as-needed and the accuracy question finally put to bed, GPS is not gonna get it done and nither is jones over roots.

If it takes more time, charge a higher fee to measure.


-b

The problem with taping is that the course is likely to change a bit every year. If taping is attempted, it would be prudent to include a number of enorute reference points. That way if the course changes, only the section between two reference points needs to be remeasured.

This potential problem is not unique to taping. Anyone who measures a long course and doesn't include enroute reference points will regret it when race management changes the route a bit for next year's race.