On Thu, 14 Feb 2008, Dr J R Stockton wrote:

In uk.transport.london message ,
Wed, 13 Feb 2008 00:21:44, John Rowland
n.co.uk posted:
and if all the satellites were exactly in a plane, there
would be no information to calculate the height.

Not so. Consider two satellites at the same height above a flat earth,
for high and low satellites, and emitting pulses simultaneously.


S1 S2









s1 s2
_____JR______________ - You X -


The delay between hearing S1 & S2 is clearly less than that between
hearing s1 & s2. JR can therefore tell, if the X-positions of the
satellites are known, how far below the satellite line he is.

True. Although now John doesn't have any reason to shout "I want these
motherf****ing satellites OFF the motherf****ing plane!", which is a
shame.

Am i right in thinking that you couldn't calculate height if the
satellites were all equidistant from you? But then you wouldn't be able to
calculate position at all. Is there a configuration where you can get a
fix in XY but not Z?

tom

--
Work alone does not suffice: the efforts must be intelligent. -- Charles
B. Rogers