GPS (Garmin) accuracy
10 watchers
Apr 2016
4:18pm, 21 Apr 2016
3,182 posts
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Nelly
PtB, your understanding agrees with the description in the "Introductory On-line theory tutorial" on the AUKCM website. So basically the guy who did it messed up, and stuck by his measurement for 3-years until the course was re-routed.
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Apr 2016
4:22pm, 21 Apr 2016
669 posts
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larkim
Update - the official web post from the coursemeasurement people say that the calibration course was short, and this accounts for half of the deficiency. Which then does imply that other races could also have similar deficiencies if the same calibration course was being used each time.
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Apr 2016
4:22pm, 21 Apr 2016
1,678 posts
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TZ
The event organisers had sufficient anecdotal and independent data to tell them the course was, at least, suspicious. They should have had it remeasured after the questionable 2013 results. The measurer made a mistake with the 2013 measurement, but it was the event which wilfully ignored the evidence.
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Apr 2016
4:29pm, 21 Apr 2016
670 posts
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larkim
Fair comment to a degree, but if you as organisers knew that you'd had it properly measured, that you were 100% certain that all of the turn points etc etc were in exactly the right place, would you think it likely that the course measurement people had actually got it wrong? They are supposedly the "trustworthy" ones in all of this, traditionally its race organisers and marshalls that get it wrong by putting bollards in the wrong place, sending people down the wrong roads etc etc. It's a little harsh to say that the organisers ought to know, when their job is to get it measured by an accredited official (tick), set the course up on the right route (tick) and make sure there were no obvious shortcuts on the route (tick). |
Apr 2016
4:48pm, 21 Apr 2016
27,254 posts
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Old Croc
as a course measurer! If you measure a course, produce a report and the organiser lays it out wrong then its their fault. If your calibration course is wrong - major oops on your behalf! nay MASSIVE oops.
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Apr 2016
4:54pm, 21 Apr 2016
27,255 posts
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Old Croc
If they out by 380m on a 42.2K mara - that's 9m / km out! So calibration course was probably out by 2-3m - I got stressed when mine was 5cm out once! You measure it with a steel tape coz fabric tapes stretch abit - but not by 3m. Number faff? Which should have been picked up - because you measure a calibration course twice - once in each direction - and 8mm per sector is considered a bit loose!
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Apr 2016
4:58pm, 21 Apr 2016
5,523 posts
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paul the builder
Nice one OC. I didn't know we had a course measurer among us.  I wonder how they realized that their calibration course (of 3 years ago) was short? And then, that only accounts for about half the inaccuracy; where does the rest come from...? |
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Apr 2016
4:59pm, 21 Apr 2016
3,183 posts
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Nelly
OC - is there a set (or minimum) distance for the calibration course?
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Apr 2016
5:09pm, 21 Apr 2016
27,256 posts
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Old Croc
Right - quick lesson. YOu measure a calibration course using a steel tape. I use a 50m tape. It is tensioned and end marked with a nail into tarmac. You then measure out a course of 150-400m - flat and straight. This is then remeasured from Finish to start. The measure for each section should be same +/- millimetres few. ie 5 or less. The length is calculated to allow for temperature (standard for a steel tape is 2o deg C) Any colder then tape is contracted / warmer expanded. This is 11 parts / million per degree. That why a calibration course is often 249.855 metres or similar. You also allow for the odd loop bit at end of a tape. Mine has a 17mm loop so you allow for that. Once a calibration course is set it should be good for several measures. Prior to each measure you ride the calibration course - to calibrate your bike / jones counter set up. You ride it twice in each direction (4) and use average count. T.his calculated counts on counter per mile or km - this is what you use to measure with. Any rounding is done against the runner - to prevent a short course - including mulitplying by 1.001 to make sure. You then ride course from start to finish - or finish to end - depends which is fixed! and which needs to be varied to fit a course. After measure ride / rides you repeat ride of calibrtaion course to ensure nothing has changedto much during ride - tyre pressure due to temperature etc Then you do calcs to make sure all was correct - they are then verified by another measurer - area secretary mainly. Cant see how a 3m error has sneaked in on calibration course! |
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Apr 2016
5:13pm, 21 Apr 2016
27,257 posts
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Old Croc
oh and don't let our very own Corrah see this - am off to measure a course for her this weekend!
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