Re: cycle cumputer results

In article <f634575a-093e-4ea7-a7c0-9d474ef9d2c5
@z4g2000prh.googlegroups.com>, DirtRoadie@xxxxxxx says...
On Oct 19, 9:52 am, Ben C <spams...@xxxxxxxxx> wrote:

Also, they don't seem to be as good at measuring elevation as they are
latitude and longitude. Don't know why that is, but it may mean that
over a hilly course there's a bigger error in the mileage.

Nope, not relevant in that regard. GPS measures distance strictly by
planar latitude/longitude position, just as you get by measuring on
map. Elevation plays no part. However a wheel-based cyclometer does
measure the actual "surface" distance covered.

GPS 'measures' latitude, longitude and altitude. The error in vertical
position is approximately 1.5 times as great as the error in horizontal
position. So if horizontal position is to +/- 12-18 m then vertical
position should be accurate to 18-27 m. It is worth noting that, due to
the irregular oblate spheroid shape of the earth, there may be an extra
'error' term in vertical position depending on the accuracy of the GPS'
model of the shape of the earths surface. So it is possible to be at th
ecoast and have a reading out by 30-40 m, but the relative change in
altitude should still be in the 20-20 m accuracy range. I think that it
is only because a typical ride might cover 30-60 km in the horizontal
direction and only 1-2 km in the vertical direction (in a really hilly
place) that the vertical resolution _appears_ to be so much worse than
the horizontal resolution of a GPS.

Mike
.

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