John F. Eldredge wrote:
> The GPS in my car is a Garmin (I don't recall the exact model at the moment).
> It appears to be much more accurate when the car is in motion than when the
> car is stationary. If I power the GPS up with the car stationary, the
> location given can be inaccurate by 100 meters or more. Once the car starts
> to move, the GPS can locate the car within 3 or 4 meters.
>
>
In automotive applications, GPS Units often use a 'snap to road'
that makes them look a lot more accurate.
My eTrex Vista HCX has two modes of computing headings: one of them
is to (i) look at the direction your track is going in and the other is
a (ii) built-in magnetic compass. If I'm moving, either in a vehicle
or on foot, I find (i) more satisfying than (ii).
The most obnoxious thing about altitude on my eTrex is that I don't
see how to get it to use GPS altitude instead of barometric altitude.
(I know how to pop up a dialog box to ~view~ GPS altitude, but that's
it.) Barometric altitude is totally useless if you're inside a
pressurized airplane. ;-)
In most situations repeatability is pretty good for me; I use
tracks for "breadcrumb navigation" all of the time on foot and rarely
see anomalies that cause practical problems. I circumnavigated the BWI
airport during a layover the other day and got at the the terminal
within 3 minutes of when I thought I would, using GPS data as the major
input to my mental calculation.
Now, I did get lost in the tunnels of the Library of Congress the
day before that... I just need an inertial guidance system for
situations like that.
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