View Single Post
  #4  
Old June 29th 06, 12:19 PM posted to rec.aviation.piloting
external usenet poster
 
Posts: n/a
Default How different is aviation GPS?

In a previous article, said:
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.


Years and years ago, I was told how to access some diagnostic modes on my
Garmin GPSMAP 195. The diagnostic mode showed the state of all sorts of
internal stuff, and from that it was apparent that one major difference
between the aviation 195 and the marine 175 is that the 195 had
temperature and pressure sensors. I suspect they put that in there so
that they could correct the results from the GPS radio for those factors.
The other major difference was that the 195 had WAY more flash memory to
store all those aviation waypoints.

But the fact of the matter is that aviation or not, GPS doesn't do
altitude as precisely as position because of the basic geometry. There
are numerous explanations of why on-line. So for aviation use, we either
need WAAS (which might or might not be available) or use a barometric
altimeter for altitude, and for surveying you let it sit so it can
accumulate a lot of data and integrate it.

As a former surveyor, I can tell you that the altitude requirements for
surveying are a lot more precise than for aviation - if my bridge abutment
is built 2 feet high, I'm getting fired. If my plane is 2 feet high,
nobody is going to notice.

--
Paul Tomblin
http://xcski.com/blogs/pt/
"All life is transitory. A dream. We all come together in the same place at
the end of time. If I don't see you again here, I will see you in a little
while in the place where no shadows fall." - Delenn