Accuracy of GPS in Garmin 430/530

"Brad" wrote in message
ups.com...
In an airplane, your immediate surroundings should have no bearing on
your GPS accuracy unless you're flying under bridges, trees, through
tunnels...you get the idea. Keep in mind that the GPS constellation is
constantly moving so there are no dead areas, like you might have with
a VOR signal. I'm not sure what you mean by deteriorating
conditions...how is your meter going to predict ionospheric activity or
a satellite going off line? It's not like bars on a cell phone.

For non-FAA rated GPS devices, it's not hard to get a bad GPS signal that is
highly inaccurate. It's not always the case that you just get a signal
failure or a good signal. Some of these GPS antennas are getting extremely
good at giving you a reading in spite of a bad positioning that blocks
important parts of the sky.


Regarding standards for handheld GPS, who would enforce the standards?
What if a particular receiver did meet the standards?

Given some number of satellites, each with a given signal quality, I think
any GPS software could make statistical calculations that would result in
two numbers for number of feet of horizontal and vertical accuracy, to some
confidence interval. How do you guarantee that the author of the software
does the math correctly? I guess you can't except by cross reference to
other devices. But the same complaint could be made about any other part
of the software. How do you know he converted spacial coordinates from the
GPS to a correct map position? No doubt there could be errors in the
implementation of those algorithms, as with any other algorithm.

--
Will