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Adjusting OPUS RS & Static Positions  

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Kent McMillan
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I know this topic has been posted numerous times, but here it goes again. This isn't any particularly novel piece of work. It's just how a survey of a 5-acre parcel was connected to NAD83. The actual point itself was a punchmark on a rod and cap monument set in a drill hole in rocky ground in a spot on the parcel that was pretty much ideal for GPS observations. L1/L2 observations were logged at 15-second intervals for 5hrs 28min and the data was submitted to OPUS in two different ways.

The first was simply sending all 5:28 of observations to OPUS Static for a solution. That position returned by OPUS-S is shown on the plot below as "1Day193opus".

The second method of positioning consisted of cutting the more than five hours of GPS observations into five 1-hr. files and submitting them individually to OPUS-RS.

The OPUS-RS solutions are 1Day193u, v, w, x and 1Day194a on the plot below.

To give an idea of the size of the residuals, here's the output listing from Star*Net:

[pre]

Adjusted GPS Vector Observations (FeetUS)

From Component Residual StdErr StdRes
To
(V1 Day193v)
1Day193v Delta-N 0.0062 0.0163 0.4
1 Delta-E -0.0133 0.0233 0.6
Delta-U 0.0452 0.1864 0.2

(V1 Day193u)
1Day193u Delta-N 0.0022 0.0119 0.2
1 Delta-E -0.0230 0.0134 1.7
Delta-U 0.0124 0.0848 0.1

(V1 Day193w)
1Day193w Delta-N 0.0254 0.0113 2.2
1 Delta-E -0.0063 0.0143 0.4
Delta-U 0.0059 0.1024 0.1

(V1 Day193x)
1Day193x Delta-N -0.0059 0.0128 0.5
1 Delta-E 0.0139 0.0107 1.3
Delta-U 0.0124 0.0903 0.1

(V1 Day194a)
1Day194a Delta-N -0.0311 0.0138 2.3
1 Delta-E 0.0078 0.0114 0.7
Delta-U 0.0026 0.1027 0.0

(V1 Day193opus)
1Day193opus Delta-N -0.0059 0.0117 0.5
1 Delta-E -0.0010 0.0064 0.2
Delta-U -0.0007 0.0155 0.0

[/pre]

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Kent McMillan
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And here are the formal estimates of the uncertainties of Control Point 1 as derived from the adjustment of the multiple OPUS solutions:

[pre]

Error Propagation
=================

Station Coordinate Standard Deviations (FeetUS)

Station N E Elev
1 0.005 0.004 0.013

Station Coordinate Error Ellipses (FeetUS)
Confidence Region = 95%

Station Semi-Major Semi-Minor Azimuth of Elev
Axis Axis Major Axis
1 0.012 0.010 173-53 0.027

[/pre]

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Paul in PA
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You Are Comparing An Apple To Applesauce, OPUS & OPUS-RS

Considering the residuals it looks like a dead heat.

Personally I would mean the OPUS-RS positions, and consider OPUS as a check. Why?

OPUS has used 2 observables, L1 & L2, against 3 CORS.

OPUS-RS has utilized 4 observables, L1 C1/P1, L2 & P2, against up to 9 CORS.

To make a more scientific comparison resubmit OPUS against the other CORS used in OPUS-RS then put the 3 solutions into Star*Net.

I would also request extended output for OPUS-RS and look at the residuals from my position to the CORS. There may be a CORS with unhappy data you want to exclude.

OPUS-RS uses a single atmospheric model for each solution. Getting rigorous, create 10 OPUS-RS submissions to see if there was any unhappy atmosphere period, in which case you may want to disregard one 1/2 session or give it less weight.

As an academic exercise you should do all I suggest but you would be chasing a very small tail.

Since your avatar shows you with closed mouth I can only surmise.

There are those that like to bite into the apple and those that prefer to not have to chew.

Paul in PA

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Dave Karoly
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You Are Comparing An Apple To Applesauce, OPUS & OPUS-RS

If you really want to go crazy you can extract the actual vectors from the OPUS extended report and adjust the giant network yourself.

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Paul in PA
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Dave, What Do You Hold Fixed ?

OPUS, holds each CORS position fixed, for three separate solutions, then means the solution.

OPUS-RS holds nothing fixed until the end, then it holds the solution as fixed and compares the observed and record CORS positions. I am not sure if Star*Net can do that.

Paul in PA

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