[time-nuts] GPS position averaging

Ole Petter Ronningen olepr01 at gmail.com
Mon Dec 15 04:03:36 EST 2014

Hello, all

I have a couple of GPSDOs (KS, z3805a) hooked up to a fixed outdoor antenna
through an HP 58516 splitter. I notice that when I powercycle the GPSDOs
(which I generally try to avoid), the position they come up with differs
from time to time in at least the last three digits (and height in
particular varies with up to 30m).

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.

Thank you!
Ole P

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