# Presentation: 809269

## O P U S

**Gerald Mader**
**Neil Weston**
**Don Haw**
**Dennis Milbert**
**Heeyul Han**

**National Geodetic Survey**
**1315 East-West Hwy**
**Silver Spring, MD**
**www.ngs.noaa.gov**

## What is OPUS?

- _O_n-line _P_ositioning _U_ser _S_ervice
- Provide GPS users faster & easier access to NSRS

## How does OPUS work?

- Submit RINEX file through NGS web page
- Processed w/ NGS computers & software
- With respect to 3 nearest National CORS
- Solution via email in minutes

## How do I use OPUS?

- Go to OPUS web page   www.ngs.noaa.gov/OPUS
- Enter your email address
- Use browse feature to select RINEX file
- Select antenna type from menu
- Enter antenna height in meters
- Option to select State Plane Zone
- Click UPLOAD
- Check your email in a few minutes

## Note: Your solutions will be archived and be publicly available. Your e-mail address will not be retained once the solution is e-mailed to you.

## How would I get Help?

- First use the Links on the OPUS page
- detailed discussions of guidelines
- description of processing techniques
- description of output
- guidelines for successful use
- Submit specific questions at OPUS web page

## What are some OPUS guidelines?

- Must submit dual-frequency (L1/L2) data
- Must submit at least 2 hrs of data
- No kinematic/Rapid Static
- No Glonass
- Correct vertical requires:
- antenna type
- antenna height

## How is the antenna height measured?

**ARP**

**MARK**

**The height is measured vertically (NOT the slant height) from the mark to the ARP of the antenna.**
**The height is measured in meters.**
**The ARP is almost always the center of the bottom-most, permanently attached, surface of the antenna.**
**See GPS Antenna Calibration for photo’s and diagrams that show where the ARP is on most antennas.**
**If 0.0000 is entered for the height, OPUS will return the position of the ARP.**

## Why do I need antenna type?

**The antenna phase centers are located somewhere around here.**

**The Antenna Reference Point (ARP) is almost always  located in the center of the bottom surface of the antenna.**

**The antenna offsets are the distance between the phase centers and the ARP**

**If the user selects NONE as the antenna type, the offsets are set to 0.000 and the antenna phase center becomes the reference**

**The user does not need to know these offsets. They are passed to the processing software through the antenna type**

**Incorrect or missing antenna type** ****** big vertical errors**

## What does OPUS output look like?

-                    **NGS OPUS SOLUTION REPORT**
**                        ****========================****      USER: gerry@mozart.grdl.noaa.gov   DATE: March 10, 2000****RINEX FILE: 0008322x.99o                 TIME: 18:55:54 UTC****  SOFTWARE: page5 0003.09               START: 1999/11/18 13:32:00**** EPHEMERIS: igs10364.eph (SP3AP)         STOP: 1999/11/18 18:05:00****  NAV FILE: brdc3220.99n             OBS USED: 9302 / 9447****  ANT NAME: ASH700936C_M          # FIXED AMB: 20 / 37****ARP HEIGHT: 2.0001                OVERALL RMS: .0188 (m)**** REF FRAME: ITRF96                  REF FRAME: NAD83****      X(m):    855249.5411  0.0192      855250.0502  0.0320****      Y(m):  -5488771.0160  0.1068    -5488772.5734  0.0891****      Z(m):   3123538.3983  0.0054     3123538.6595  0.0329****       LAT:  29 30 48.37447 0.0473    29 30 48.35598 0.0385****     E LON: 278 51 23.39245 0.0323   278 51 23.40223 0.0179****     W LON:   81 8 36.60755 0.0323     81 8 36.59777 0.0179****    EL HGT:       -25.5803  0.0916         -24.0442  0.0865****BASELINE LENGTH(m)****0008 TO ccv3 130479.3953 ****0008 TO cha1 380400.1523 ****0008 TO eky1 264510.5766**
**This position was computed without any knowledge by the National Geodetic Survey regarding equipment characteristics or field operating procedures.**

## How are OPUS positions computed?

- NGS PAGES software
- Ionosphere free
- Tropospheric scale height adjusted
- Fixed ambiguities
- Average solution to 3 nearest CORS
- ITRF and NAD83 positions reported

## How are OPUS errors estimated?

- Overall root mean square
- Peak to Peak errors
- allows 3 redundant baselines
- computed separately for ITRF and NAD83
- max coordinate spread from 3 CORS
- better indicator than rms