Posted By Deral at Home on 11/9/2008 at 12:36 PM
others who missed this OPUS (length) submission/post by Loyal , here is
the link to some background information on this discussion.
thanks for all your time explaining some of the finer points of what
you have to contend with in the moving part of the word and also in
what I need to be aware of even in my stable little burg.
all the information in the links and scroured the NGS for further
information as well as some of your sources other links.
Fact. OKLW (local CORS) is showing a very distint easting bias of 1.8cm for the shown period on the 60 day plots.
Fact. We have no time series to look at the overall picture.
Is this a system bias, some shift in the actual mounts recently, a bent
support rod or something else. We cannot tell by the 60 day plots. As
far as I know, this small building that the antenna is mounted on could
have settled or moved that much over a period of time in our soils.
It appears that the time series is in fact a huge improvement over the 60 day plots.
have systematic biases that will tend to stabilize and using the entire
time series can be plotted and graphed as one or more CORS falls out of
spec and is need of an upgraded position to better fit in the national
You can correct based on the 60 day estimates (and they
are estimates) but that does not tell you the full story like the time
My interest in this has sparked anew with our very soon
to be purchased RTN for Lawton. I expect to tie this station to our
network and use our current NSRS derived coordinates for this station.
concern is other stations that may pop up which could be used in our
town. I dont' see this as a very big risk since we are geographically
distant from any other large towns and our corrections will be free to
anyone that wants to use our network.
Granted that we are
chasing very small numbers in a system that is not entirely error free.
We have tropo, iono and all the other noise factors that figure into a
I did a pretty simple test. All reported in US Feet and I just showed the important digits.
Run One with OKLW using OPUS.
Run Two with OKLW Excluded.
So where did the 1.8 cm go, which is around 0.05'. Did it get squished out in the adjustment of OPUS?
this a reason that the NGS has decided not to change a coordinate
before some threshold? They felt that the difference would not be
noticable to 99.9% of the users.
Sometimes I think I may be confusing myself.
OPUS-DB, 60 day series and others.
November 10, 2008