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CORS. CORS. CORS Network. > 1,865 Stations 226 federal, state, local and academic partners Growth > 231 new stations in 2012 Updated Guidelines. CORS “Data Products” Page. Obtain Static Data Files for CORS Here. CDOT CORS/OPUS Team.

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Cors network
CORS Network

  • > 1,865 Stations

  • 226 federal, state, local and academic partners

  • Growth > 231 new stations in 2012

  • Updated Guidelines


CORS “Data Products” Page

Obtain Static Data Files for CORS Here

Cdot cors opus team

  • Incorporate CORS and OPUS into the CDOT Survey Manual

  • Test Data Assessed

  • Written Report Provided to CDOT

  • Presented to SAC on Feb 15, 2012

  • Addendum – use of CORS added

  • Recommendations also made

Online positioning user service opus
Online Positioning User Service (OPUS)

  • Users submit GPS data to NGS

  • Data is processed using NGS computers and software

  • Resulting precise positions e-mailed back to the user

  • Solutions up to 1-2 cms in accuracy provided by email

  • OPUS Rapid Static - 15 minutes of data vs. 2-4 hours


  • OPUS – S (2 hrs)

  • OPUS – RS (15 minutes)

  • OPUS – DB (Publish)

  • OPUS – Projects (Network)


Online Positioning User Service (OPUS)

  • >15 min of L1/L2 GPS data >>>

  • Processed automatically on NGS computers, tied to CORS

  • Solution via email - in minutes

  • Fast, easy, consistent access to NSRS


Static: OPUS determines your position with a differential GPS static solution, using hours of data.

This process is repeated 4x from other CORS.

solution 2

CORS solution #1

solution 3

solution 4

solution 5

How good can i do with opus s
How Good Can I Do With OPUS-S?

More generally, Eckl et al. (NGS) preformed a similar but more extensive test using the same software but outside OPUS.

Eckl et al., 2001, “Accuracy of GPS-derived relative positions as a function of interstation distance and observing-session duration”, J. of Geod. 75, 633-640).

Their results provide a good “rule of thumb” for accuracy versus session duration when using OPUS-S and in many other applications.


Rapid-static: OPUS first creates an atmospheric delay model from surrounding CORS data.

Your position is then quickly determined by differential GPS static solution.

How does opus rs work
How Does OPUS-RS Work?

  • OPUS-RS selects three to nine “best” CORS based upon:

    • Having common satellite visibility with the user data.

    • Having distances from the user’s site <250 km.

  • This is shown here graphically. The star represents the user’s site. The triangles are CORS.

  • No CORS farther than 250 km from the user’s site will be included.

  • The three CORS minimum is shown.No more than nine are used.

  • s



    Choi, 2010, personal communication.

    How does opus rs work1
    How Does OPUS-RS Work?

    In addition, user’s site must be no more than 50 km from the (convex) polygon created by the selected CORS.

    Again in this figure, the star represents the user’s site; the

    triangles are CORS. Five CORS and their resulting polygon are shown in this example.

    If the user’s site, the star, is more than 50 km outside this polygon, alternate CORS will be considered.

    If none can be found, the processing will abort.

    Schwarz et al., “Accuracy assessment of the National Geodetic Survey's OPUS-RS utility”, 2009, GPS Solutions, 13(2), 119-132.


    solution 2



    your position:averaged from the “best” 3 of 5 CORS solutions


    CORS solution #1




    solution 3

    your peak-to-peaks:scaled from the spread of the 3 CORS solutions

    solution 5



    solution 4

    How is the antenna height measured



    • 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 the default height of 0.0000 is entered, OPUS will return the position of the ARP.

    How is the Antenna Height Measured?

    Why do i need the antenna type

    phase ctr.

    Why Do I Need the Antenna Type?

    The antenna phase centers are located somewhere around here.

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


    You do not need to know these offsets. They are passed to the processing software through the antenna type

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

    Incorrect or missing antenna type big vertical errors

    Ngs antenna calibration relative vs absolute gnss antenna calibration



    NGS Antenna Calibration –Relative vs. Absolute GNSS Antenna Calibration

    2 hours

    GPS tracking

    Ngs data sheets
    NGS Data Sheets


    blue booking



    Opus db requirements
    OPUS DB Requirements

    Field Procedures

    • GPS data file ≥ 4 hour duration

    • quality mark setting

    • experienced observer

    • fixed height tripod recommended

    • brace tripod legs with sandbags or chain

    • verify antenna height and plumb

    Opus db requirements1
    OPUS DB Requirements

    High-Quality OPUS Solution

    • ≥ 70% observations used

    • ≥ 70% ambiguities fixed

    • ≤ 3 cm RMS

    • ≤ 4 cm peak-to-peaks, lat. & lon.

    • ≤ 8 cm peak-to-peak, el. hgt.

    • properly identify antenna type

    • precise or rapid orbits (avail. next day)

    Opus db requirements2
    OPUS DB Requirements

    Mark Attributes

    • photos of mark & equipment

    • details (name, type, stability, etc.)

    • description to aid mark recovery

    • preview mark description form& help file


    • OPUS-projects:

    • first, run OPUS to harvest all project data

    • OPUS automatically forms sessions from simultaneously observed marks, allowing multi-baseline processing and adjustment of multiple sessions.

    Opus projects
    OPUS Projects





    • OPUS-NET:

    • first, run OPUS to solve for CORS from IGS CORS

    • then run OPUS-Static using improved CORS positions and tropospheric corrections, along with ocean-tide loading & absolute antenna calibration models


    • What’s happening now?

    • PAGES suite (software behind OPUS) to integrate GLONASS and other GNSS.

    • Updated algorithm for OPUS-RS

    Heights geoid new datums grav d
    HeightsGeoidNew DatumsGRAV- D