"BTIZ" > wrote in message
news:0Pu5c.16807$Nj.10761@fed1read01...
> [...] granted with minor errors of cheap handheld GPS
> units

The "minor errors" exist in all GPS units, no matter the cost. There aren't
any error-free GPS units available.

Not all GPS receivers perform to the same standards, but they all have
errors. No amount of money will change this.

Pete

It is working perfectly... The erratic motion when standing still is due to
two major items...
One, is the fact that your built in antenna is not recovering the data
stream as consistently as an external antenna will - are you sorrounded by
buildings?... Go out into an open area away from trees and buildings, or get
an external antenna and it will quiet down...
Second, the nature of gps is that there is a circle of confusion around the
fix point... The more satellites your unit sees with consistent data the
smaller the circle of confusion..
When your unit is dithering what is the EPE and DOP showing? I just ran out
to the car to check mine and the EPE is 28 feet, and the DOP is 1.7... The
heading was stable... The altitude was bouncing around about 4 to 5 feet
with variations in the data stream...
Do a google on gps and read up on the technology a bit...

cheers ... denny
"Glenn Westfall" > wrote in message
...
> I have a Garmin 196 and just in the past week or so it is acting
> strange. I get a signal just fine, but when I am standing still it
> constanly changes headings. It never moves in a direction, just turns
> in circles sporatically. Once I begin to move, it tracks just fine.
> But as soon as I stop, it constantly changes headings again. Anyone
> else experience this? I upgraded to the latest software, but that
> didn't fix the problem.
>
> Glenn

On Mon, 15 Mar 2004 19:49:16 -0800, "BTIZ" >
wrote:

>GPS only computes heading from "last known position" to "current position",
>if you are not walking.. the "last known and current" are the same.. there
>is no heading to compute.. granted with minor errors of cheap handheld GPS
>units.. the "movement" could be minor inches or parts of an inch as the GPS
>computes it's position.. and that will cause a heading change..

It is actually quite a bit more than inches. Single carrier civilian
GPS without SA (which has been shut off for several years now) is
accurate to about 10-20 meters. With WAAS corrections, it is about 3
meters.

The delta between any two position estimates is several inches to
several feet. Most GPS software will mask this motion and force the
velocity display to 0.0, and the heading display to be fixed, however,
if the delta between two position estimates is large enough, it can
generate a false movement.

-Nathan

On Tue, 16 Mar 2004 03:14:29 GMT,
(Glenn Westfall) wrote:

>I have a Garmin 196 and just in the past week or so it is acting
>strange. I get a signal just fine, but when I am standing still it
>constanly changes headings. It never moves in a direction, just turns
>in circles sporatically. Once I begin to move, it tracks just fine.
>But as soon as I stop, it constantly changes headings again. Anyone
>else experience this? I upgraded to the latest software, but that
>didn't fix the problem.

On my Garmin 295, I had to re-enable WAAS after upgrading software.
WAAS significantly improves the performance of the GPS, and may make
the differences in calculated motion between two position estimates
small enough to force the velocity to 0.0 and the heading to be fixed.

-Nathan