Hmmm, I was just going by experience with a Garmin consumer grade
hiking GPS about 5 years ago. You could literally hold it in your
hand, walk a few steps, and it would give you a reasonably accurate
heading (say, within 20 deg, although I didn't rigorously test it)

A GPS fix has several types of error (this is a rather generic analysis):

1) zero-mean noise on the time-scale of seconds
2) zero-mean noise on the time-scale of minutes/hours
3) a constant (over an hour, say) mean error which depends upon your
position, which satellites you see, etc.

A single position fix has all three sources of error. Averaging over
seconds reduces #1, averaging over hours reduces #2, DGPS partially
allows you to eliminate #3.

A velocity estimate isn't affected by #3 at all. Some sensible
averaging and assumptions about how you can move can be built into the
GPS's filtering algorithm so that #1 and #2 are reduced. This leads me
to believe that a velocity estimate has the potential to be quite
accurate.

Sean




On Tue, Apr 28, 2009 at 7:37 PM, Carl Denk <cdenk@windstream.net> wrote:
> Typically a moving type GPS (not a land surveyors or other using DGPS
> local station, or averaging over a period of time) =A0will be +/- 30 feet
> or so. Lets take an extreme, 60 foot error between readings, along with
> 1000 foot of travel, then arc tangent of 60/1000 =3D 3.4 degrees. But the
> unit will be taking many readings in a minute. WAAS (or the Russian
> equivalent) will be a little better. Some units may average the track
> direction. I have used the unit to find cemetery grave markers, after
> previously setting a waypoint to the marker with good success, in
> particular when after vising several times, each time adjusting the
> waypoint =A0location by averaging the old and new locations. I use the map
> then to determine what direction to walk. =A0Sorry to say I haven't paid
> attention to the track direction indicated, or whether WAAS was active.
>
> I have a Lowrance Expedition C hand held. For short distances of travel,
> say maneuvering in a small parking lot or small street intersection,
> trying to figure out the direction of travel, or where you want to go is
> not dependable. The unit does have a built in compass which works fine
> when =A0a passenger of the foot (walking), but inside a vehicle, is
> useless, with errors of 90 degrees or more, even after compensating in
> the vehicle.
>
> Sean Breheny wrote:
>> A good GPS
>> receiver should be able to get heading info from even fairly slight
>> motion - you don't need to drive it down a road.
>>
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