Endurance.Net Ridecamp Archives

Tx Trigger wrote:
> Nancy posted: >>>. I have a Garmin GPSmap 60cs that I have been using to
> mileage a trail for a new ride. <<<
>
> I have the same GPS, and we have used it to mark mileage markers on the
> local trail system. We would ride the trail a few time, and hang a ribbon
> each time we hit a mile. We found that even after riding the trail in
> different conditions, clouds, no clouds, winter with little foliage on
> trees, and summer with lots of tree cover, the GPS was really close each
> time to previous marker ribbons. Maybe off by 50' or so sometimes???  I'd
> trust it to be accurate enough to give the mileage to the riders as such,
> even if this is a NATRC ride, where we give mileage points along the way.

I use both a Forerunner 350 and a GPSMap60csx.  Both have proven to be 
accurate in nearly all conditions.

As to concerns about going up and down hill leading to inaccuracy, this 
is not really a problem.  If you remember your high-school trigonometry, 
the distance added by going uphill or downhill compared to going across 
a flat surface is quite small -- a lot less than it feels like.  Even a 
ten-percent grade -- a steep climb -- adds only one percent to the 
distance over that climb.  Since most of the trail even on mountain 
rides is nowhere near that steep, the error over 50 miles due to 
uphill/downhill is trivial.

Deep canyons are a problem, but not as bad as "concrete canyons" in big 
cities.  There are few trails with deeper canyons than the Big Horn 100, 
 and when I plotted my tracks from that ride onto aerial photographs, 
it was only down in the bottoms of the very deepest canyons that the 
track ever deviated from the trail.  That made the readings on those 
legs of the trail short by no more than one percent, if that much.

I used a mechanical wheel (pushed by hand) to measure my trails back 
when I was managing rides.  That is the only method I would trust more 
than today's good-quality GPS units.


--
Joe Long
jlong@xxxxxxxxxxxxx

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