Mr Thant wrote:
On 12 Feb, 14:10, "John Rowland"
wrote:
It doesn't give height, though. Is it hard for GPS to be used to
determine height above sea level?

A GPS receiver works by narrowing down your position in three-
dimensional space, so figuring out your altitude and figuring out your
location are inseparable.

If only three satellites are visible, the locus of possible locations is a
straight line in space which intersects the earth's surface at two points.
Knowing which satellites are visible enables you to eliminate one of these
points, but it doesn't give you the height. Even if quite a few satellites
are visible which were all roughly in a plane, there would be low precision
on the height, and if all the satellites were exactly in a plane, there
would be no information to calculate the height.