Re: errors in GPS reported height

Craig Fink <WeBeGood@xxxxxxxxx> wrote:

If you think of it as strictly a geometry problem, where each GPS
satellite give you your position as a sphere, with the radius being your
distance from the satellite.

One important thing to keep in mind is that the length of the radius
is just a wee bit indeterminate. The surface of the sphere has a
non-zero thickness.

So, you can probably see why it's a harder problem to determine altitude.
It's the Earth, it's constraining the geometry of the problem for altitude
more than it is Latitude and Longitude.

And if you look at the overall situation at the time of the specs
being set you can see why they didn't worry about altitude;

Users on the ground - can look up their altitude on a topo map if they
actually care that much.
Users at (or under) the sea - "we are at sea level idiot, look out the
porthole/periscope".
Users airborne at high altitude - precise altitude matters little
Users airborne at low altitude - "quit looking at the gadget dammit
and help me watch for hills, trees, and powerlines!"

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
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