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#MTB J U N E/ J U LY 2019 VO L 59
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MEASURING RACE ROUTES
HOW DO THEY GET IT SO £$%@ING WRONG
We have all been there: 67km into a 65km race, with nary a sight nor sound of the finish. TIM BRINK set out to see how and why event organisers get this so wrong, or right. And who need the Altitude Adjustment Klap.
t all started with a semi-heated discussion in the Full Sus offices. A recent Absa Cape Epic finisher was still fuming, a fortnight later, that the elevation projected in the event literature had been considerably off. He is one of the three types of GPS-watchers we see in events; the climber, the how-far-to-go-er and the tikkel-tokkel. Our visitor was the first – he plans his day by knowing exactly what is coming from a climbing perspective, adjusting his input and output by judging how hard he needs to push to make X-hundred meters of ascent in the remaining Y kilometres. We tend to find this A-type towards the sharp end of the field, with the middle- to backmarkers focussing more on the distance covered and to go. The rarest of the three, the third mentioned, simply doesn’t care, riding for riding’s sake and enjoying his surroundings over his electronica. The reality for event organisers today is that just about every entrant will have a swish, ‘accurate’ GPS unit, and will be convinced that their reading by the end of the ride is the correct one, no matter what. Unfortunately, it isn’t that easy. Let’s start by looking at the different ways it would be possible to measure these routes. The most accurate would be to take one of those measuring wheels we occasionally see men with hard hats walking along highways with. Calibrated by the SABS, these are dead-accurate, but logistically, I don’t think we can expect an event organiser to go quite this far. In any case, the distance side of things is the easier of the two to get right with GPS technology; it is the altitude gain and loss that is more challenging. GPS units measure this in one of two ways, or in a combination of both: barometrically or through the mapping on the device. The former uses a little air-pressure gizmo in your device (you will see little holes somewhere underneath it, the latter relies on the accuracy of your GPS to know where you are, and tells you how high you are on the map. The better devices use a combination of both, with an algorithm creating a best-case scenario. Some firms use a barometric base, with a GPS correction, others do it the other way round (some even use different combinations within their range, which will explain why model A differs from model B).
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