GPS navigation

I've been watching this discussion in the sci.geo.satellit-nav newsgroup,
and my reaction to your friend's ideas is "What an idiot."

Bob Gardner

"David W" wrote in message
oups.com...
Hello to all,

Do most modern aircraft rely on the GPS for navigation, and to what
extent do they rely on it?

And is it true that such aircraft's navigation systems use maps
'optimised' for GPS?

And finally, if I may, what level of positional accuracy must aircraft
relying on GPS for navigation work with at typical altitudes
(presumably 20,000 to 40,000 ft)? Are we talking tens of metres, or
over a hundred metres?

Thanks very much in advance.


Regards,

David,
England.

Bob Gardner wrote:
I've been watching this discussion in the sci.geo.satellit-nav newsgroup,
and my reaction to your friend's ideas is "What an idiot."


My post to that group requesting advice and comment was way too long; I
imagine it made for quite tedious reading, which I don't think helped
my case as much as it might have done.

But I'm happy with the replies (in that group and certainly here),
overall :-)

My opponent, even though he evidently knows next-to-nothing about the
GPS, or GPS survey, is trying to discredit a set of GPS coordinates
that has cost me time, energy and lots of money to obtain (obtained
with diligence and after a sufficient number of hours of research (in
my opinion)). And he thinks I should use theodolites and trig points
instead of GPS.


Thanks to all that have replied.


Regards,

David,
England.

To address the question of optimized maps for aviation use, if that indeed
is relevant to this discussion, he should go to an outlet that sells
aviation maps and ask for a GPS-optimized map. I think that he will be
surprised.

Bob Gardner

"David W" wrote in message
oups.com...
Bob Gardner wrote:
I've been watching this discussion in the sci.geo.satellit-nav newsgroup,
and my reaction to your friend's ideas is "What an idiot."


My post to that group requesting advice and comment was way too long; I
imagine it made for quite tedious reading, which I don't think helped
my case as much as it might have done.

But I'm happy with the replies (in that group and certainly here),
overall :-)

My opponent, even though he evidently knows next-to-nothing about the
GPS, or GPS survey, is trying to discredit a set of GPS coordinates
that has cost me time, energy and lots of money to obtain (obtained
with diligence and after a sufficient number of hours of research (in
my opinion)). And he thinks I should use theodolites and trig points
instead of GPS.


Thanks to all that have replied.


Regards,

David,
England.

"David W" wrote

My opponent, even though he evidently knows next-to-nothing about the
GPS, or GPS survey, is trying to discredit a set of GPS coordinates
that has cost me time, energy and lots of money to obtain (obtained
with diligence and after a sufficient number of hours of research (in
my opinion)). And he thinks I should use theodolites and trig points
instead of GPS.

Ask him how modern surveyors locate points on property.

Hint. GPS.
--
Jim in NC

In article 0o_ig.19660$8q.17433@dukeread08, "Mark Manes"
wrote:

You need at least 3 satellites in view to get an accurate 3D position.

4 satellites unless you already know GPS time or know your altitude.

--
Bob Noel
Looking for a sig the
lawyers will hate

Somebody with whom I am having a 'debate' has asserted
that there is an altitude-dependent error component

The distance to a station using DME is "slant range", the distance to
that same station using GPS is a projection, so some slight error is
introduced there. It is possible that your friend is mis-interpreting
or mis-applying this tidbit.

"Aircraft ... are using a map optimised to the GPS system and this is
the key point which seems to be passing you by."

There are several geoids in use, and the choice of geoid may introduce
position errors. A geoid is a surface of equal gravitational potential
(a "mean sea level") and is an idealized surface - the real earth has
bumps and wiggles which are modeled imperfectly (or not at all) in some
models. Your friend may also be mis-applying this tidbit.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

David,

GPS is optimised for sea level, Blanchefort [a mountaintop ruined
castle] is 467 metres above sea level, couple this with a slant range
to a satellite of several thousand miles and the curvature of the earth
and you have error. At least up to 100 metres..."


That's just plain BS. Just one example: The space shuttle uses GPS for
navigation. That should be plenty high to convince the poster otherwise.

--
Thomas Borchert (EDDH)

Mark,

You need at least 3 satellites in view to get an accurate 3D position.


4. You need to correct for receiver clock error.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote:
That's just plain BS. Just one example: The space shuttle uses GPS for
navigation. That should be plenty high to convince the poster otherwise.

Would an ordinary GPS receiver (say, my $99 eTrex) work on the shuttle? I
can see how the basic principles are the same, but I'm guessing my eTrex
wouldn't be happy with the speeds the shuttle is doing.

Roy,

I
can see how the basic principles are the same, but I'm guessing my eTrex
wouldn't be happy with the speeds the shuttle is doing.


Many cheaper GPS receiver do indeed have a speed limit. Is it given in the
specs for the eTrex?

--
Thomas Borchert (EDDH)