GPS - Practical Short-Term Accuracy?

Author

Practical Short-Term Accuracy?

Jeff Maass

2007-01-16, 10:33 pm

I have a Garmin GPSmap 60CSx, but I think that my question is a general one
concerning GPS functionality.

If I walk a line from point A to point B in, say 3 minutes, how much
confidence should I have in the distance between them reported by the GPS
device? Is it repeatable (that is, if I immediately walk back to point A,
will the GPS reflect that I've arrived within, say, a foot?

I understand that absolute accuracy is limited, but how is the relative
accuracy over a small distance and a small time?

peter

2007-01-16, 10:33 pm

Jeff Maass wrote:
> I have a Garmin GPSmap 60CSx, but I think that my question is a general one
> concerning GPS functionality.
>
> If I walk a line from point A to point B in, say 3 minutes, how much
> confidence should I have in the distance between them reported by the GPS
> device? Is it repeatable (that is, if I immediately walk back to point A,
> will the GPS reflect that I've arrived within, say, a foot?
>
> I understand that absolute accuracy is limited, but how is the relative
> accuracy over a small distance and a small time?

It may not be much better than the absolute accuracy. Even though
you're returning to the same place, the receiver may be using a
different set of satellites due to minor changes in orientation or any
obstructions (such as the user's body). If it is, then the effects of
tropospheric delays and other sources of error will be different on the
position determination.

Sam Wormley

2007-01-16, 10:33 pm

peter wrote:
> Jeff Maass wrote:
>
> It may not be much better than the absolute accuracy. Even though
> you're returning to the same place, the receiver may be using a
> different set of satellites due to minor changes in orientation or any
> obstructions (such as the user's body). If it is, then the effects of
> tropospheric delays and other sources of error will be different on the
> position determination.
>

Try: http://users.erols.com/dlwilson/gpswaypt.htm

nospam@nospam.com

2007-01-17, 4:33 am

I find that my trip computer is not very accurate for distance but my track log
is right on.

On Wed, 17 Jan 2007 04:01:49 GMT, in alt.satellite.gps Sam Wormley
<swormley1@mchsi.com> wrote:

>peter wrote:
>
> Try: http://users.erols.com/dlwilson/gpswaypt.htm

Jeff

2007-01-24, 10:33 pm

Although you are stationary to the earth the satellites are moving about
7500 mph and in addition the earth's rotational velocity in the US is about
700 mph so even you move a short distance your position relative the
satellites has changed quite a bit. Therefore the error you get being
stationary in one location will be similar any other comparable location
(number of satellites visible, etc) so the difference will be the square
root of the sum of the squares of the errors just lots of other types of
measurement. In this case the errors are the same so that the error would
be about 1.4 times the error in one location.

"Jeff Maass" <jmaass@columbus.rr.com> wrote in message news:45ad99b8$0$5182

$4c368faf@roadrunner
.com...
>I have a Garmin GPSmap 60CSx, but I think that my question is a general one
> concerning GPS functionality.
>
> If I walk a line from point A to point B in, say 3 minutes, how much
> confidence should I have in the distance between them reported by the GPS
> device? Is it repeatable (that is, if I immediately walk back to point A,
> will the GPS reflect that I've arrived within, say, a foot?
>
> I understand that absolute accuracy is limited, but how is the relative
> accuracy over a small distance and a small time?
>
>
>
>
>
>
>

LinkBot