PC Software for Garmin GPS

Peter said:

Michael J. Klein said:

On Wed, 16 Jun 2004 21:12:27 -0700, Peter <[email hidden]>
wrote:

Quoted message said:

Quoted message said:

Quoted message said:

Do the recent versions allow you to plot the elevation profile using the
altitude data from the GPS? I have version 2 and it uses the DEM topo
data to generate the profile just using the horizontal position data

Quoted message said:

from the GPS tracklog. Unfortunately the DEM data is not very accurate.

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.
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
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
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.

Which is exactly what the autocalibration feature of the Garmins which
have barometric altimeters does, e.g. Garmin eTrex Vista & Summit,
76S, Geko 301, 60CS. Much more stable and accurate altitude readings,
plus altitude accuracy which is maintained when GPS accuracy degrades,
or when satellite lock is temporarily lost. The downside is
occassionally ridiculous altitude readings for some time after switch
on, unless you can be bothered to check for miscalibration and correct
it manually.

--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]