Violating Airspace with GPS

"Mike Beede" wrote in message ...
In article , Ron Natalie wrote:

Your information on RAIM is wrong. What is unique about the RAIM used in IFR
approved GPS's is not that it determines when the satellite geometry is giving you
an error NOW, but computes if it will fail while during the expected duration of flying
an instrument approach.

That's RAIM *prediction*. RAIM is very capable of failing during an approach if
you don't check the prediction ahead of time, at least on our Garmin 430.

Yes...and if you read his document, he doesn't distinguish between RAIM (which many
non-IFR units do just fine) and predictive rain.

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

That's RAIM *prediction*. RAIM is very capable of failing during an
approach if
you don't check the prediction ahead of time, at least on our Garmin
430.

Yes...and if you read his document, he doesn't distinguish between RAIM
(which many
non-IFR units do just fine) and predictive rain.

Ron,

I am open to argument and corrections of any misunderstandings that I might
have. It was my impression that RAIM is strictly a integrity monitoring
scheme rather than a predictive function. RAIM uses redundant satellite
signals as a cross check to monitor whether any satellite signals are bad.

Since a GPS knows the satellite orbits from the almanac, a program can be
designed to predict if satellite positioning will be adequate to support
RAIM at a given time and place. Receivers such as the Garmin 430 have this
RAIM prediction feature. Knowing the satellite orbit information, it is
also possible to predict and issue a notam for areas and times when RAIM
will be unavailable.

Using the same techniques for predicting RAIM coverage, it would be possible
to warn of impending satellite geometry and coverage problems. I do not
know whether or not any GPS receivers do this automatically beyond the RAIM
prediction program such as in the AUX menu of the Garmins.

I guess I understand RAIM as a monitoring the integrity of the satellite
signal rather than a predictive function. However, I will agree that there
are ways to predict whether or not RAIM will be available.

I am open to corrections if you will explain your reasoning and possibly
site sources.

Thanks,

John Bell

"John Bell" wrote in message ...
That's RAIM *prediction*. RAIM is very capable of failing during an
\
I am open to corrections if you will explain your reasoning and possibly
site sources.

I believe you understand it, now go back and read your book. It is NOT the
presence of RAIM that distinguishes the IFR GPS's (many non-IFR GPS's
also have it), it's the predictive feature that is required/distinguishing.

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



--
(for Email, make the obvious changes in my address)

On Mon, 03 Nov 2003 17:38:07 +0100, Thomas Borchert
wrote in Message-Id:
:

IMHO it [GPS] gives you more than positional awareness.

Aside from ground speed, and three dimensional position (and time of
day), what other information does GPS provide?

Although the aircraft's position is displayed relative to geographical
features (roads, rivers, towns, ...), most GPS databases do not
contain terrain data. GPS doesn't tell you anything about the
powerplant(s), ATC, traffic, fuel, in flight and destination weather,
pilot health, ... which are all part of situational awareness.

Here's one definition of situational awareness:

http://www.refresher.com/!pilot.html
Situational awareness is an ongoing process of the continuous
assessment and accurate interpretation of reality. Effective
environmental scanning when combined with the awareness of the
performance capability of the aircraft, and the self awareness of
personal capabilities and skill of the pilot result in competency
and precision in the execution of maneuvers, and flight safety.


More he
http://aviation-safety.net/events/FCV.shtml
http://www.acespilotshop.com/pilot-s...-awareness.htm
http://www.hpti.net/aviation/situational.html

Larry,

Aside from ground speed, and three dimensional position (and time of
day), what other information does GPS provide?


Wind speed and direction, for example.

GPS doesn't tell you anything about the
powerplant(s), ATC, traffic, fuel, in flight and destination weather,
pilot health,

Larry, I never said it would. Not with one word. I know all the stuff
you provided for my education.

Let's stop the nit-picking and get back to the original topic: The
statement was that, while GPS is nice, moving maps don't do much for a
pilot. I disagree. Strongly.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote

Wind speed and direction, for example.

How??? By itself, a GPS cannot do this. Only as a part of a
Flight Management System (or similiar NAV System) with an
input of TAS and HDG can wind speed and direction be computed.
A GPS will only provide TRK (course made good) and GS of the
six item wind triangle.... HDG, TAS, TRK, GS, Wind DIR, VEL.

Bob Moore

On Tue, 04 Nov 2003 16:00:48 +0100, Thomas Borchert
wrote in Message-Id:
:

Larry,

Aside from ground speed, and three dimensional position (and time of
day), what other information does GPS provide?


Wind speed and direction, for example.

I wasn't aware of that. What GPS has the capability to display wind
speed and direction?

GPS doesn't tell you anything about the
powerplant(s), ATC, traffic, fuel, in flight and destination weather,
pilot health,

Larry, I never said it would. Not with one word.

The phrase you used, situational awareness, implies those things.

I know all the stuff you provided for my education.

Then please display your knowledge of that "stuff" by using the
correct terms.

Let's stop the nit-picking and get back to the original topic: The
statement was that, while GPS is nice, moving maps don't do much for a
pilot. I disagree. Strongly.

Your disagreement is apparent. Unfortunately, in this message thread,
you fail to provide any examples of evidence that supports your
contention.

You contend that moving-map GPS is second only to the AI in its
usefulness, but you don't say how it's useful. Your opinion is always
welcome, of course. But the logic you used to arrive at that opinion
would be significantly more useful information, IMHO.

Larry,

Ok, you had your fun jerking my chain, so let's let it go. If you fail
to see the usefulness of a moving map display, I can't help you. Just
don't use one!

--
Thomas Borchert (EDDH)