[time-nuts] GPS position averaging

Bill Hawkins bill at iaxs.net
Mon Dec 15 19:19:42 EST 2014

This may be one of those cases where the human brain's ability to see
patterns would help to see the distribution and eliminate outliers. Plot
a manageable set of X and Y points, and another set of X and Z points. 

To make the three dimensions plot as one in a statistical distribution
(bell) curve, use the magnitude of the vector.

What do the surveyors instruments do that can get them down to a few
centimeters in half an hour?

You might also want to study what's been said about the causes of
variance. The atmosphere is not uniform.

Consider the relative effect of position on time, where one foot or 30
cm is equivalent to 10E-9 second.

Also consider the 'averaging' period of the PLL filter in the
disciplined oscillator.

I'm no expert, especially not in math. These hints are thoughts that
come to mind.

Bill Hawkins

-----Original Message-----
From: Ole Petter Ronningen
Sent: Monday, December 15, 2014 3:04 AM

I would like to get a better idea of what my actualt antenna location
is, so that I can manually set the position in the GPSDOs. For that
purpose I set up a Ublox M8N with logging in U-center, and I've
collected about 250K readings over several days. For each reading I also
log number of SV's used, as well as HDOP, VDOP. PDOP, thinking I would
filter the list and end up with a subset of really good fixes.The idea
is then to average the "best readings" and use that as my position.

My question is twofold; 1) is this for some reason a bad idea? And 2)
How do I average the numbers? I can not put my finger on it but it
"feels wrong" to average lat, long and height independently.

Any hints are greatly appreciated.

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