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'[ot]: calculating average GPS position'
2003\04\24@225151 by

how exactly would I calculate an average of a fixed gps reciever
to eventually get a more accurate lat/lon ??

if you take two lat/lon's average, then do this with the very next available
lat/lon
is this any good?

or if you take 10 lat/lon's get average then average this with the next ten

what's the best way to do this?

thanks

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Not specifically w.r.t. GPS, but from a mathematical perspective...

If you're suggesting averaging by averaging points A & B, then the result of that with C, then with D, etc, that would be an incorrect definition of the term "average".  Avg(A,B,C) != Avg(A,Avg(B+C)).  For example, the average of 7,8,9 = 8.  Avg(Avg(7,8) , 9) = Avg(7.5,9) = 8.25.  Bzzzt!

So take all lats and avg those, take all lons and avg those, and that should be the result.

Or maybe there's something specific to GPS that makes this all just a load of cr*p?

Cheers,
-Neil.

On Thursday 24 April 2003 21:49, rad0 wrote:
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the gps data constantly streams in
so, when you say 'take all' what does that mean?

I'm not quite sure what a moving average is, formula wise, but is this what
you need to do?  calculate a moving average?

thanks

{Original Message removed}
For what it's worth;

I can't find the reference for it at the moment but I recall reading that
(now obsolete) would take 1000 samples to determine its location when in the
'survey' mode. The VT
receivers were apparently used primarily in a fixed location as a time
reference and/or (I think) as a source of correction data for DGPS.I don't
remember if it said at what rate the samples were taken,
once a second or less often. I would guess that it only used lat.and Lon.
that had a DOP (Dilution of Precision) of less than three. (As I write this
I have 6 satellites in view
but with a DOP of only 3.3.)

The Motorola test software shows (and plots) a continuous Least Squares
Average and a continuous
Mean average of latitude and Longitude. (It only averages them when the DOP
is <= 3.)

Quite a lot of Motorola information can be found at
http://www.synergy-gps.com/Mot_Manuals.html

Mike Jones

{Original Message removed}
>Or maybe there's something specific to GPS that makes
>this all just a load of cr*p?

HMM :))

I have a Motorola Oncore OEM board, and have been playing with it to get
fixed locations. It is quite interesting to see the "onscreen position" of
the Oncore monitoring program that Motorola supply for use with their
receivers. You will be surprised how the apparent position wanders around,
suddenly jumps 20 feet etc. This program can also show two different mean
positions with uncertainty circles, and the two can be that far apart that
they are more than the combined uncertainty circles apart. The program also
has a function for doing fixed point plotting, but I do not know what
optimisations it does to come up with stable data points.

Try logging the GPS output to a spreadsheet for an hour or so at say 1
minute intervals, and then plotting the resultant data. This will give you a
feel for what you are up against.

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However, you don't have to keep all the individual values around. Just
maintain the sum of the lats and longs and the number of points, and then
divide at the end. KISS.

You will see a modest improvement (statistically) in position accuracy as
you average more samples. IIRC, the improvement is proportional to the
square root of the number of samples averaged.

Bob Ammerman
RAm Systems

{Original Message removed}

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