How different is aviation GPS?

As part of my work (civil engineer), I routinely use GPS equipment in
surveying. And construction specifications usually calls for this
equipment to be held stationary for as much as three hours where
crucial transition points are to be located, and for up to twenty
minutes at less important locations.

I guess since you folk use GPS to navigate all across the globe and
requires to be both very precise and instantaneous, my equipment is
very much inferior to what's used in aviation.

Has anyone here used the type of equipment I'm mentioning? You should
see the time the thing I use takes to stabilize itself to show the
elevation... you'd comfortably CFIT if you had that in your airplane
)

Ramapriya

In article .com,
wrote:

[snip]
Has anyone here used the type of equipment I'm mentioning? You should
see the time the thing I use takes to stabilize itself to show the
elevation... you'd comfortably CFIT if you had that in your airplane

yeah, but what is the accuracy of your GPS?
I suspect it is much more accurate than needed for aviation.

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

Bob Noel wrote:

[snip]
Has anyone here used the type of equipment I'm mentioning? You should
see the time the thing I use takes to stabilize itself to show the
elevation... you'd comfortably CFIT if you had that in your airplane

yeah, but what is the accuracy of your GPS?
I suspect it is much more accurate than needed for aviation.


Not really Bob. Most building, refinery and pipeline surveys accept a
+/- 0.8 centimeter variation, so it isn't pinpoint like in aircraft, I
think.

Btw, just out of interest - does TCAS use GPS data in some ways too?

Ramapriya

In article .com,
wrote:

Not really Bob. Most building, refinery and pipeline surveys accept a
+/- 0.8 centimeter variation, so it isn't pinpoint like in aircraft, I
think.

+/- 50+ meters is plenty accurate enough for aviation use in determining
lateral position. +/- 10 meters vertically would be wonderful but not always
obtained.


Btw, just out of interest - does TCAS use GPS data in some ways too?

No.

ADS-B does, but not TCAS.

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

Bob Noel wrote:

+/- 50+ meters is plenty accurate enough for aviation use in determining lateral position. +/- 10 meters vertically would be wonderful but not always obtained.


I confess I couldn't have guessed that )


Btw, just out of interest - does TCAS use GPS data in some ways too?

No.

ADS-B does, but not TCAS.


Thanks, but how exactly does the TCAS get the coordinates of the
transponder it talks to, in determining whether or not an evasive
mechanism needs setting in? Anything like a +/- 50 meter accuracy there
would be disastrous.

Ramapriya

wrote in message
ups.com...
Thanks, but how exactly does the TCAS get the coordinates of the
transponder it talks to, in determining whether or not an evasive
mechanism needs setting in? Anything like a +/- 50 meter accuracy there
would be disastrous.

TCAS typically uses the transponder output to determine altitude of the
other traffic, and basic radio direction and range-finding processing to
determine direction and distance.

For the purpose of TCAS, +/- 50 meters is perfectly sufficient. Alerts are
provided at distances much greater than that, and an error of 50 meters
would affect the timing of the alert by a second or less. When in a
congested area, where TCAS is most typically important, airplanes are
traveling on the order of 50-100 meters per second.

You seem to be under the impression that flying involves a very high degree
of accuracy with respect to position information. That's simply not true.
Even in a differential GPS precision approach or a Cat III ILS, accuracy is
only to within a meter or so, and for anything else tens, hundreds, or even
thousands of meters is sufficient (depending on the exact situation).

In addition, while you are relying on your GPS receiver for altitude,
airplanes almost never do. They have barometric altimeters that provide a
different reference (not necessarily more accurate...just different) that is
more appropriate for the operation of an airplane (generally speaking). So
the GPS data is used only in two dimensions, in which the instantaneous
accuracy is generally much better, as compared to 3D accuracy including
altitude.

Your demand for accuracy in construction is FAR greater than any need
aviation has. As far as the difference in the GPS receiver goes, it is
likely that the basic operation of the GPS receiver you are using is
identical to that of an aviation handheld.

That said, I'm surprised you are using sample averaging to gain the accuracy
you need. Surveyors do use differential GPS with great success, and it
provides similar accuracy to what you're getting, only in a matter of
seconds rather than hours. (DGPS used for surveys has better accuracy than
that used for aviation because the reference point is so close to the
measured location in the case of surveying, whereas it may be quite a
distance away for aviation).

Pete

wrote:
Bob Noel wrote:
[snip]
Has anyone here used the type of equipment I'm mentioning? You should
see the time the thing I use takes to stabilize itself to show the
elevation... you'd comfortably CFIT if you had that in your airplane
yeah, but what is the accuracy of your GPS?
I suspect it is much more accurate than needed for aviation.


Not really Bob. Most building, refinery and pipeline surveys accept a
+/- 0.8 centimeter variation, so it isn't pinpoint like in aircraft, I
think.

I had my property surveyed and asked what the accuracy was. The
surveyor replied that 0.1 foot is the standard for most applications and
0.01 foot is required for commercial, high-precision applications.
They use GPS (DGPS??) but I don't know how.

In a previous article, Stubby said:
I had my property surveyed and asked what the accuracy was. The
surveyor replied that 0.1 foot is the standard for most applications and
0.01 foot is required for commercial, high-precision applications.
They use GPS (DGPS??) but I don't know how.

You need a better surveyor. When I was doing road construction layout, we
were expected to get the marks within 5-7 millimeters. And when they
actually did the construction, they were allowed to be within 2-3
centimeters. (You've heard the expression: measure with a micrometer,
mark with chalk, cut with an axe.) Legal surveyors were supposed to be
*far* more accurate than us. For instance, we just held the chain (that's
the "measuring tape" to you) or laid it down on the ground. Legal
surveyors had a special device to make sure they were holding exactly the
right amount of tension on the chain because that's what it was calibrated
for.

--
Paul Tomblin http://xcski.com/blogs/pt/
ALL programs are poems, it's just that not all programmers are poets.
-- Jonathan Guthrie in the scary.devil.monastery

You also attach a thermometer to the tape because there is a
correction for expansion. If the tape was supported by the
ground, a tension of 10 pounds was required if I remember
correctly.


"Paul Tomblin" wrote in message
...
| In a previous article, Stubby
said:
| I had my property surveyed and asked what the accuracy
was. The
| surveyor replied that 0.1 foot is the standard for most
applications and
| 0.01 foot is required for commercial, high-precision
applications.
| They use GPS (DGPS??) but I don't know how.
|
| You need a better surveyor. When I was doing road
construction layout, we
| were expected to get the marks within 5-7 millimeters.
And when they
| actually did the construction, they were allowed to be
within 2-3
| centimeters. (You've heard the expression: measure with a
micrometer,
| mark with chalk, cut with an axe.) Legal surveyors were
supposed to be
| *far* more accurate than us. For instance, we just held
the chain (that's
| the "measuring tape" to you) or laid it down on the
ground. Legal
| surveyors had a special device to make sure they were
holding exactly the
| right amount of tension on the chain because that's what
it was calibrated
| for.
|
| --
| Paul Tomblin
http://xcski.com/blogs/pt/
| ALL programs are poems, it's just that not all programmers
are poets.
| -- Jonathan Guthrie in the scary.devil.monastery

Aircraft systems are designed to rather wide standards,
measured in meters and not the centimeter accuracy of a
surveyor's system. An aviation GPS will lock on to all
visible satellites and begin giving navigation solutions
within just a few minutes. The aviation and
automotive-marine-hiker GPS include a navigation computer
and will to some degree do all the calculations and display
results. Your impression about aircraft accuracy is 100%
backwards.


You can find the specifications for GPS systems on the
Garmin or other makers web sites.


wrote in message
oups.com...
| Bob Noel wrote:
|
| [snip]
| Has anyone here used the type of equipment I'm
mentioning? You should
| see the time the thing I use takes to stabilize itself
to show the
| elevation... you'd comfortably CFIT if you had that in
your airplane
|
| yeah, but what is the accuracy of your GPS?
| I suspect it is much more accurate than needed for
aviation.
|
|
| Not really Bob. Most building, refinery and pipeline
surveys accept a
| +/- 0.8 centimeter variation, so it isn't pinpoint like in
aircraft, I
| think.
|
| Btw, just out of interest - does TCAS use GPS data in some
ways too?
|
| Ramapriya
|