MapSource Elevation Question

For the first time, I uploaded Track and WayPoint data from two recent
hikes using my GPSmap 60CX and was able to plot a vertical profile of
the hikes complete with elevations and distances over the entire 10
miles of track data.

Two Questions:

1. Where are these elevations coming from? MapSource? There's nothing
on Mapsource to indicate topography and elevations. I don't believe my
GPSmap 60CX can determine elevations.

2. How accurate are these elevations, assuming they're coming from
MapSource?

Elevations are nice to know from the device itself. Maybe I should have
bought the 60CSX?

Many thanks for any light shed on this.

wrote:


GPSRs can get elevation data from the satellite fix, but it's relative
to the imaginary sphereoid it thinks you're standing on.

The "S" (sensor) models have a barometric altimeter which reports your
altitude based on the ever-changing barometric pressure, and unless you
know how to calibrate it, probably won't be any more accurate than the
satellite-derived numbers.

--
Bert Hyman        St. Paul, MN        bert@iphouse.com

Bert Hyman wrote:
Well, thanks Bert.
I just checked one of the Track locations, and yep, there is a satellite
derived altitude. Somehow, I missed that.

Why do you say it's relative? It's simply calculated, no different
from your Lat/Long, right?

On Wed, 11 Aug 2010 13:29:47 -0500, Sunshine wrote:


The spheroid defines the zero-point.

The satellite data could give you the distance from the center of the
earth, but that's not the usual reference for altitude; mean sea level or
the assumed spheroid are possible references.

--
Gene E. Bloch (Stumbling Bloch)