On Sat, 03 Mar 2012 09:13:45 +0100, Helmut Wabnig [email protected] ---
-.dotat wrote:

Youre asking wrong questions.
First define a surface with height ZERO as a reference.
There are about 100 different definitions alone for that.
Distance from Earth center, median sea level at Novosibirsk,
or a San Francisco? Water isn't level, it follows gravitation.
And so on.

w.

If in the US, I would assume that the LAT/LONG uses either WGS84,
NAD27, or NAD83 datums. That reduces the number of available options.

Unfortunately, the USGS is still hanging onto NAD27, while most
mapping programs and displays are on WGS84.
http://www.maptools.com/UsingUTM/mapdatum.html
In the People's Republic of Santa Cruz, the error is about 20 meters
east-west, and about 1 meter north-south. I forgot which way. The
problem becomes really bad when trying to locate a mountain top.
20-200 meters of horizontal error can easily move a position from the
peak, to somewhere on the slope, resulting in large altitude errors.

SRTM and SRTM2 are another oddity. They were created from the space
shuttle, using a radar altimeter. Depending on the whether it's
looking at buildings or trees, there's no really good way to determine
of the indicated altitude is the top of a 100ft redwood tree, the top
of a 10 meter high building, or at ground level.

So, my list of rhetorical questions a
1. What is the OP trying to accomplish? If for an FCC license HAAT
calculation, almost any reasonable guess will suffice.
http://transition.fcc.gov/mb/audio/bickel/haat_calculator.html
If for doing Radio-Mobile coverage contours, you'll need to use the
built in mapping tool to find the peak or exact location on the
mountain top. The choice of application depends on what one is
attempting to accomplish.
2. What level of accuracy is really required? The original position
of 37.337408N -121.644073W is specified to 1 millionth of a degree, or
about 0.09 meters.
http://www.csgnetwork.com/degreelenllavcalc.html
It would be interesting to know where this highly accurate number came
from. Better GPS receivers, without DGPS, can do 3 meters accuracy.
3. What datum are you using? I suggest WGS84. If the lookup tool
offers a choice of datums, pick one and stay with it.
4. Are you interested in ground level, building rooftop level, or
tree top level?

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS