OPUS RS & Star*Net Setup (GPS Factor)

> My first question is with respect to the .GPS FACTOR. How do I determine what value to use?

I'd say that experience is the best guide. In Central and West Texas a value of 2.5 is a good choice with twice that for the vertical. The inline commands are:

[pre]
.GPS WEIGHT COVARIANCE
.GPS FACTOR 2.5 VERT 5.0
.UNITS METERS
[/pre]

>
> My second question is with respect to the estimation of Point #50. Am I correct in thinking that Point 50 does not exist until Star*Net adjusts and estimates its value? Further, is this estimated value based on multiple RS observations that I input into Star*Net from their respective extended reports?

Point 50 is the adjusted point. If you have only one OPUS solution, Point 50 will have the same coordinates as the OPUS solution, but will have an uncertainty based upon the covariances in the G2 and G3 lines that were taken from the OPUS solution.

>
> Below, I have pasted the setup with only one observation of 50Day258a. The matrix information was gleaned from the extended report.
>
> Am I on the right track?
>
>
>
> .GPS WEIGHT COVARIANCE
> .GPS FACTOR ????
> .UNITS METERS
>
>
> # BASE STATIONS USED
> #PID DESIGNATION LATITUDE LONGITUDE DISTANCE(m)
> #DM4654 INPA PAOLI CORS ARP N383357.706 W0862930.634 55275.7
> #DJ5204 LOU6 LOUISVILLE 6 CORS ARP N380037.882 W0851755.323 66223.4
> #DM4658 INSY SEYMOUR CORS ARP N385736.280 W0855142.432 68428.2
> #DM4660 INTC TELL CITY CORS ARP N380336.152 W0863732.842 69161.9
> #DM3503 INMD MADISON CORS ARP N385003.079 W0852516.188 69722.3
> #DK4051 KYTD KY HWY DIST 4 CORS ARP N374054.459 W0855102.411 73964.1
> #DN2113 KYBU GEN BUTLER SRP CORS ARP N384025.770 W0850917.721 76338.5
> #DM4638 INBD BEDFORD CORS ARP N385147.104 W0863120.304 77563.3
> #DM4650 INJS JASPER CORS ARP N382430.048 W0865619.271 88937.6
>
> PH 50Day258a 38-20-44.18466 85-55-26.45075 226.100 !!!
> G0 'V50 Day258a
> G1 50Day258a-50 0 0 0
> G2 0.0000008189 0.0000298600 0.0000179100
> G3 -0.0000030370 0.0000022560 -0.0000224900

The format looks reasonable to me. I'd have to see the covariance matrix returned by OPUS to verify that the G2 and G3 lines were properly formed.

As a practice tip: I think it works well to put the OPUS solutions in their own GPS files. I usually give a separate file to each OPUS point, OPUS_CP50.gps, etc. That sort of things. Multiple OPUS solutions on the same point would go in the same file.

I have never used the GPS FACTOR inline option. I scale the supplied standard errors globally through the use of the "Factor Supplied Standard Errors" setting in the GPS Options dialog.

On that subject, 10 years ago error multipliers were routinely 5, 10, or more. Lately the multiplier I end up using is much closer to 1. The collection software must be getting better at estimating errors.

> I have never used the GPS FACTOR inline option. I scale the supplied standard errors globally through the use of the "Factor Supplied Standard Errors" setting in the GPS Options dialog.

If you have multipe OPUS solutions on the same point and they are all together in one .GPS file, it makes sense to turn off all the other input data and run just the OPUS solutions to see how will the global factor fits. If it doesn't, the inline command can adjust the GPS FACTOR to a more realistic choice.

That's how I derived the values of GPS FACTOR that I use.

Thanks for the replies. To further expand...

Norman -> For your method, in 'Project Options,' under the GPS tab, 'OPUS Stations' heading, the box 'Factor Supplied StdErrs by:' should be checked. Where in the OPUS report does this StdErr get reported?

Kent -> If I choose to enter my own GPS FACTOR, how do I evaluate if the GPS FACTOR I choose is a good one (more specifically)? Should I be looking in the Output of the Star*Net file for something specific as it relates to the Supplied StdErr?

Thanks. Please excuse my ignorance.

> Norman -> For your method, in 'Project Options,' under the GPS tab, 'OPUS Stations' heading, the box 'Factor Supplied StdErrs by:' should be checked. Where in the OPUS report does this StdErr get reported?

Collect enough data for OPUS-S and ask for the "extended" report. Save all the text in the email you get from OPUS to a txt file. Then import that txt file to StarNet. For each OPUS point you will get a block of data like this:

[pre]
.Units Meters

## File: s:dks (dks associates)dks-29 (mill plain)dks29-field datagpsopus (ur) 141023.txt
## GH 1129 -22.717
P 11 45-37-29.58655 122-35-27.94038 89.972
WV1 3.3390000000E-006 1.9569000000E-006 4.1419000000E-006
WV2 -5.7190000000E-007 5.6910000000E-007 5.6510000000E-007
[/pre]

Those WV lines are your errors. And I was in error in my first post. For OPUS stations, the "Factor Supplied Standard Errors" settings are at the bottom of GPS tab of the Project Options dialog box, separate from the "Factor Supplied Standard Errors" for vectors that is in the top part of that same dialog.

This is for Version 7 of the software. Note that this only works for OPUS-S. It doesn't support OPUS-RS. I understand that version 8 has added support for OPUS-RS but I don't have that yet.

> Kent -> If I choose to enter my own GPS FACTOR, how do I evaluate if the GPS FACTOR I choose is a good one (more specifically)? Should I be looking in the Output of the Star*Net file for something specific as it relates to the Supplied StdErr?

The simplest way is to run an adjustment with several repeat OPUS solutions on the same station and do that by itself. Turn off all of the other data files and just run the .GPS file with the OPUS solutions in it.

The Error Factor in the statistical summary for GPS Vectors should be nominally 1.0, if the GPS FACTOR value(s) is well chosen.

Ideally, the more repeat solutions, the better. The way I work, I like to leave a receiver on a centrally located, secure control point for most or all of the working day. So after several days on the project, I have hours and hours of data to either be submitted to OPUS-S or to be cut up into shorter files using teqc for OPUS-RS solutions.