On Fri, 18 Jun 2004 07:42:24 -0700, Peter <[email hidden]>
Quoted message said:Michael J. Klein wrote:
<snipped stuff>
Quoted message said:Quoted message said:Neither is GPS alititude. If knowing the altitude is important, use
an alitmeter.
Quoted message said:No measurement is perfect, but I've found GPS-derived altitudes to be
far better than the DeLorme DEM data. The DEM-derived profiles tend to
show considerable up and down variation on roads that actually have a
very even grade. The overall shape of the profile is pretty good but
the cumulative climb is greatly exagerated.
No doubt taken from USGS topo maps from the 70's or earler.
Quoted message said:Here's a sample elevation plot using only GPS data from two bike rides
over the same course on different days to check for consistency:
http://home.comcast.net/~prathman/Image33.gif
Nice image!
Quoted message said:A barometric altimeter (I presume this is what you mean by 'alitmeter' -
a GPS is also a form of altimeter) by itself is subject to considerable
I just meant a device which is specifically designed to resolve an
altitude, not one which does it as a secondary function.
Quoted message said:variation due to changing atmospheric conditions and is generally less
trustworthy than careful GPS measurements unless frequent recalibration
is feasible. Much better is using the two together with the pressure
sensor providing short-term stability and the GPS correcting for
longer-term atmospheric changes.
I've only played with an eTrek, so I haven't checked out the accuracy
of both methods combined. Its gotta be better than having just one of
either.
If I understand the application, isn't grade and distance the real
data which is important to cyclists? Don't you wanna know the incline
and how far, and not necessarily the specific altitude? If so, why
not just use a slope meter?
Michael J. Klein [email hidden]
Dasi Jen, Taoyuan Hsien, Taiwan, ROC
Please replace mousepotato with asiancastings
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