1. Online Positioning User Service Review and new developments
OPUS
Online Positioning User Service
Review and new developments
Scott Lokken
NGS State Advisor (NC)
work
cell

2. Positions and Elevations from GPS Static Occupations
Different Flavors of OPUS
OPUS Rapid Static (15min to 2 hrs)
OPUS Static (2 hours +)
Sharing (Optional)
OPUS Projects (Network Least Squares solution)
OPUS Net (Under development)
GNSS (Under development)

3. OPUS Static limitations
Dual-frequency data (L1/L2)
[recommended] Minimum 2 hrs of data (maximum 48—only cross midnight once)
No kinematic data
No Glonass. Galileo will be discussed
as the constellation becomes available
Some of the OPUS Guidelines are
the data must be dual frequency (for now)
it should be at least 2 hours in duration
No kinematic or rapid static
No glonass
You must supply the correct antenna type and height,
or I wouldn’t bet on the results of the vertical component
And the file name should be the standard 8.3 CORS naming convention.
Accurate height requires:
correct antenna type
correct antenna height

4. How Does OPUS Work? Data submitted through NGS web page
Processed automatically with NGS computers & software
Positioned (Tied) to suitable CORS
Solution via (usually in minutes)
Don’t forget—it is FREE
OPUS works by Submitting data through the NGS Web page
It is Processed automatically with respect to 3 CORS
3 independent single base line solutions are performed in the ITRF (International Terrestrial Reference Frame) using the PAGES software and then averaged together.
The Same thing but different is done for the Nad83 computations.
You can read all about it under the “discussion” button on the OPUS home page
If everything is working as it should you can usually expect results in just a few minutes.

5. How Does OPUS Static Compute Position?
OPUS Chooses Three best CORS
Then 3 single baselines computed
3 positions averaged —
simple mean (equal weights)
Differences between positions include any errors in CORS coordinates

6. OPUS-RS search algorithm
250 km limit
<50 km
Sort stations in CORS network by distance from rover. Select up to nine CORS that are less than 250 km from rover and that have suitable data.
No solution is attempted if fewer than three CORS selected.
No solution attempted if distance from rover to polygon enclosing selected CORS is greater than 50 km.

7. Recent Changes -New Web page and interface
-Absolute Antenna Calibrations
-MYCS coordinates available

11. OPUS Static
Metadata
statistics
metadata
NAD83
ITRF
SPC and UTM

12. OPUS Rapid Static Obs used >60
quality ind. < 1 might have problem
Normalize residual<1 is desirable

13. What to look for? your antenna type and antenna height are correct
orbit used = precise or rapid
OPUS-static
90% data used
50% Ambiguities solved
RMS< 3cm
Peak to Peak < 5cm
3cm horz
5cm vert
OPUS-rs
Obs used >60
quality ind. < 1 might have problem
Normalize RMS <1 is desirable
Rapid Static:
-No warning messages.
-Quality indicators that are suspiciously low Normalized RMS that is suspiciously high.
-Coordinate standard deviations that are suspiciously high.

15. Trouble fixing ambiguities
Short session
Trouble fixing ambiguities
Result: High peak to peak errors (poor solution)

16. Extended Output Note: Peak to peaks are fairly large; hoz @ 15 cm
Vrt @ 23 cm
Example of extended output.
Solution was from applanix base in middle of median going to Wilmington. Poor visability and examining the PDOP after the fact, a poor window for most of the session.

21. Running the poor APPLANIX base session again ommitting Castle Hayne

23. How Can I Improve My Results?
-The best way to get more accurate results is to observe longer sessions.
-Data sets of at least four hours have been shown to result in more reliable results.
-Pre-plan your survey. Make sure your not observing in a poor GPS window.
-Set your GPS in an unobstructed area including away from and higher than your vehicle. (preferably use a fixed height pole)
-Use an antenna with a ground plane.

24. Calculating horz/vert accuracies OPUS Static solution report
Horizontal positional accuracy calculation at 95% confidence
Vertical positional accuracy calculation at 95% confidence
VertAccuracy = height peak to peak value

25. OPUS Rapid Static
OPUSrs reports Root Mean Square Error (RMSE) results at 1 sigma (68% confidence interval).
Horizontal positional accuracy at 95% confidence:
*2 methods--dependent on the RMSE values*
#1 if: RMSElat = RMSElong
Horizontal accuracy = x RMSE
#2. if: < RMSEsmaller/RMSElarger <1.0
Horizontal accuracy = x 0.5(RMSElat + RMSElong)

26. OPUS Rapid Static (cont)
OPUS reports Root Mean Square Error (RMSE) results at 1 sigma (68%).
Vertical accuracy at 95% confidence:
Vertical accuracy = 1.96 x (RMSEorthometric height)

28. Slide showing database and search

32. OPUS Projects

33. OPUS Projects Submit Data to OPUS static
Include recovery info, description and photographs
Combine multiple observations into a session
Perform a least squares adjustment of all sessions

34. Future developments OPUS NET Will Replace OPUS static
Use new algorithm for processing
Least Squares instead of mean
Different style output
Includes usFt in SPC!
In testing for over a year, and rumored to go live soon.
GNSS
Working on adding to both NET and RS

35. Questions?
Questions???
Breath!!!