Difference Between 1 Long Observation & Multiple Short Observations

Jim Frame

Active Member
This came up in a conversation with John Evers a couple of days ago. Neither of us knew the answer, so I thought I'd throw it out there in the hope that someone with an understanding of RTK inner workings will chime in.

The question: What's the difference between taking, say, a single observation of 180 epochs, versus 3 observations of 60 epochs, versus 18 observations of 10 epochs, assuming that all 3 scenarios occur within the same 180-epoch span? Are the longer shots simply averaging the epoch-by-epoch positions, or is something more sophisticated (and presumably useful) going on behind the scenes?
 

Jim Campi

Active Member
Jim, what RTK verification settings are you using?

I'm sure you know more about this than I do, however my understanding is that resetting the RTK engines and restablishing a fix increases the accuracy/precision.
 

Jim Frame

Active Member
I've currently got my unit set to a minimum of 2 engines fixed, but I don't know think that matters with regard to the original question. What I'd like to know is whether the receiver is able to extract accuracy and/or confidence from a single long RTK observation that it can't obtain from multiple short observations taken within the same time window.
 

Matt Johnson

Well-Known Member
5PLS
No, epochs are just averaged together during longer observations the same way as they are during short observations. If you were to average your multiple short observations together you should get the same result as the single long observation.

The purpose of resetting the RTK engines is to verify that the ambiguity fix is resolved correctly, in other words it is checking that you don't have a bad fix.
 

Jim Campi

Active Member
Jim,

Modify the RTK verification settings to

v6 with reset

And compare your solution to

V6 w/out reset.
 

Nistorescu Sorin

Active Member
Hi Jim,

Solution quality and robustness in case of a RTN scenario can be improved by implementing either single or double-window position averaging.

For topographic survey applications, a 5 second single-window average reduces the effect of individual coordinate solution variations, but for more precise work, using two sets of averaged windows of around 3 minutes separated by around 20 minutes may cause 10-20% coordinate accuracy improvements compared with a single epoch solution.

The separation period is driving down short period system biases. This can be further improve to up to 30% if the double window separation is extend to about 45 minutes, but beyond this separation no appreciable improvement can obtain.

For base-rover scenario some interesting things can be found here:
http://www.javad.com/jgnss/support/video.html at structure monitoring video.

Regards,

Sorin.
 
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