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GPS (Garmin) accuracy

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Corona Apr 2016 12:33pm, 21 Apr 2016 3,920 posts	Quote Pin Corona So we all know that our garmins etc. aren't accurate, but it seems they're accurate enough to identify a short course :-D coursemeasurement.org.uk
HappyG(rrr) Apr 2016 12:41pm, 21 Apr 2016 25,534 posts	Quote Pin HappyG(rrr) Good statistical analysis here, if anyone is interested nrem.iastate.edu
HappyG(rrr) Apr 2016 12:46pm, 21 Apr 2016 25,535 posts	Quote Pin HappyG(rrr) Ah, I see your thread is more about apologies by Course Measurers for Manchester. Not just 2015 but 2014 and 13 too. Will records for those years have to be changed? Re. GPS though, it sounds like while it was prompted by GPS users (i.e. the runners) it was only an official re measurement that proved it was the course, not the GPS that was wrong. It doesn't mean that in other courses and races, a GPS measurement might be wrong, not the course. I'd say that our GPS devices are still wrong more often than course measurers or race organisers are wrong? Or am I being naïve? G
tonyp2604 Apr 2016 12:49pm, 21 Apr 2016 342 posts	Quote Pin tonyp2604 Ian put a link to this useful Guardian article he wrote: theguardian.com
larkim Apr 2016 12:54pm, 21 Apr 2016 656 posts	Quote Pin larkim Quite an admission though by the course measurers. Good that they are honest enough to admit that it is their error, rather than the organisers. Will be galling to those for whom 380m made the difference between meeting their targets or narrowly missing them. 100s of running or so for someone at 7min/mile, just over 2 minutes for 9 minute milers.
CharlieP Apr 2016 3:02pm, 21 Apr 2016 81 posts	Quote Pin CharlieP I think the moral of the story is that while any one GPS device isn't going to be completely accurate, when you aggregate the results from a large enough number you can have confidence that a course needs to be re-checked. Exactly the same thing happened at the inaugural Mansfield half marathon last year - enough people complained that the distance seemed to be out that they checked and put their hands up to having made a mistake.
Surrey Phil Apr 2016 3:17pm, 21 Apr 2016 1,414 posts	Quote Pin Surrey Phil I've heard it said that when measuring an already identifiable distance, such as an athletics track, a satellite measuring system such as Good Run Guide or MapMy Run is more accurate than if using a Garmin.
larkim Apr 2016 3:22pm, 21 Apr 2016 667 posts	Quote Pin larkim This is a list of courses measured by the same chap that measured the Manchester route which is now found to be out. I wonder if any of these were done with the same Jones wheel which now appears to have been discovered to be out of calibration? certno course_name distance datemeasured 2014097 Wilmslow Half Marathon 13.109375 miles 2014-01-20 2013354 Capesthorne Half Marathon 13.1094 miles 2013-10-20 2013325 Cowm Reservoir 5k 5 Km 2013-09-18 2013316 Arley 10k 10KM 2013-09-08 2013304 Congleton quarter marathon 10 Km 2013-08-26 2013303 Congleton Half Marathon 13.109375 miles 2013-08-26 2013267 Stockport 10 Mile Road Race 10 miles 2013-07-15 2013190 Arley Half Marathon 13.109375 miles 2013-05-26 2013188 Macclesfield Half Marathon 13.109375 miles 2013-05-26 2013161 Buxton Carnival 4 Mile 4 miles 2013-04-26 2013069 Greater Manchester Marathon 26.218 miles 2013-03-04 2013042 Buxton 5km 5 Km 2013-02-19 2012365 Tatton Half Marathon Half Marathon 2012-10-30 2012212 We Love Manchester 10k 10Km 2012-05-28 2012211 Oldham Half Marathon Half Marathon 2012-05-27 2012193 Macclesfield 5km 5 Km 2012-05-04 2012150 Salford 5K 5 Km 2012-03-16 2012122 Salford 10K 10Km 2012-03-16 2012057 Greater Manchester Marathon 26.219 miles 2012-02-12 2012049 Littleborough 5km 5 Km 2012-02-03
paul the builder Apr 2016 4:05pm, 21 Apr 2016 5,522 posts	Quote Pin paul the builder My understanding of course measurement is not that the wheel is either calibrated or not calibrated; it's that before each measurement they perform a calibration routine by measuring a known distance and then count the revs or clicks or whatever of the wheel - and then use this as a scale factor when it comes to calculating the distance of the proposed course. So the fact that the wheel has grown, shrunk, or had a tapeworm super-glued to its circumference doesn't matter since there's a re-calibration before each measurement.
larkim Apr 2016 4:15pm, 21 Apr 2016 668 posts	Quote Pin larkim Yes, on reflection that's mine too - it should be done over a known distance both before and after the course measurement takes place to account for pressure changes, other issues etc etc. So I suppose my premise is wrong - its unlikely to be a badly calibrated wheel, its more likely that something has gone awry in the calculations etc, which I'm sure the measurer will feel really bad about.