Violating Airspace with GPS

Robert,

I do indeed remember meeting you in Lakeland. Whenever I see one of your
posts, it is like picking up a paper and seeing a byline from a reporter
that I respect.

Actually, my response to Ron Natalie was a little more than tongue in cheek.
It was somewhat of a combination of defensiveness and worry that I might be
spreading bad information. Ron's statement that my explanation of how GPS
works: "while one of the common ones often espoused
has no basis in reality. This is not how GPS works" has me curious.

Unfortunately, Ron's statement unfortunately gives me little to correct my
understanding if it is indeed wrong. Luckily, even if my explanation of how
GPS works is totally incorrect, it should not have serious consequences as
far as usage is concerned.


John

"Robert Moore" wrote in message
. 7...
Larry Dighera wrote

There are very knowledgable folks willing to answer all your
questions there.

:-) :-) Since John has written texts on GPS Navigation, I suspect
that he was pulling someone's leg.

http://www.smallboatgps.com/ http://www.cockpitgps.com/


Hi John, how's things going? Remember meeting at SnF?

Bob Moore

"John Bell" wrote in message . com...


Actually, my response to Ron Natalie was a little more than tongue in cheek.
It was somewhat of a combination of defensiveness and worry that I might be
spreading bad information. Ron's statement that my explanation of how GPS
works: "while one of the common ones often espoused
has no basis in reality. This is not how GPS works" has me curious.

The "overlapping spheres" model is NOT how GPS works. It's the same as the
stupid flashing light analogy for VOR. It perhaps gives someone some concept,
but it's not accurate at all. The way GPS works is to use pairs of satellites
to determine hyperbolids which are intersected with ones generated from other
pairs.

The "overlapping spheres" model is NOT how GPS works. It's the same as
the
stupid flashing light analogy for VOR. It perhaps gives someone some
concept,
but it's not accurate at all. The way GPS works is to use pairs of
satellites
to determine hyperbolids which are intersected with ones generated from
other
pairs.



Ron,

I looked up some information. I have not had time to completely digest it,
but I do see how a GPS system could be designed to use pairs of satellites
with hyperboloids. I think that my explanation is sufficient for a pilot
level operational understanding of how GPS works. Among other sources
propagating a similar explanation are Trimble and Garmin, so at least I am
in good company. My purpose is to provide a brief conceptual idea of how
GPS works. The primary purpose of my text is to provide practical guidance
as to how to actually use GPS.

Trimble's explanation is at http://www.trimble.com/gps/how.html. And
Garmin's "GPS for Beginners" is available at
http://www.garmin.com/support/userMa...ory=53&product
=999-99999-20

I did a Google search,
http://www.google.com/search?hl=en&i...id+GPS&spell=1 , and
did find some sources indicating that positioning could be done using pairs
of satellites and the intersection of hyperboloids. I am not sure if GPS
receivers actually use the intersecting hyperploids or intersecting sphere
model in their actual design. It appears that both are different techniques
to solve the same problem.

I am not an electrical engineer and am not sure which explanation is correct
or if they are merely different solutions to the same problem. I appreciate
you responding back to explain why you think my explanation was wrong.


John Bell
www.cockpitgps.com

The way GPS works is to use pairs of
satellites to determine hyperbolids which
are intersected with ones generated from
other pairs.


That's the way sailors do it, but they do it by hand using hyperboloids plotted
on their charts.

If there is a mathematically equivalent way to do it, it might be one that is
easier to program into a box, and maybe that's what an aviation GPS does. If
the alternative is not mathematically equivalent, then one of them is just
wrong.

Jose



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