Re: gpsprof: higher resolution

[Gerry Creager - NOAA Affiliate]

Hal

What would you like specifics on? Besides decimation... 

Decimation does indeed mean dropping at least consecutive positions, especially when they're not presented on the satellite observables. I'll let you read about autocorrelation of measurements if you're not already aware of the concept. Simply put, most GPS's providing code-phase positioning use the last determination as a first-guess for the next determination, and then account for movement, consistent movement vectors, etc., If you're trying to determine position with NMEA output, this becomes a problem and you'll see some wandering of position. 

If you're using raw observables this is not an issue, although the geodetic processing I've used tended to randomly remove an observation or two to decouple obs. 

I can go into more detail if desired.

73

gerry n5jxs

On Sun, Aug 16, 2020 at 14:59 Hal Murray <hmurray@megapathdsl.net> wrote:

gerry.creager@noaa.gov said:

> Also, a caveat I'm sure you're aware of, is before you simply average your

> NMEA data, decimate it to reduce the impact of autocorrelation in the

> standard position output.



Could you please say more.  That sounds like something I should understand but

I don't get it.



What does "decimate" mean in that context?  Do I just throw away 9 out of 10

samples?  Or average blocks of 10 then take their average?  The latter sounds

like a dodge for numerical precision.  My back of the envelope says it should

fit in a double.



How does autocorrelation get involved and/or how does it screw things up?





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