Geodetic Control/OCRTN

Geodetic Control

The Geodetic Unit is responsible for maintenance of the Horizontal and Vertical control networks. Responsibilities include updating, revising and distributing the most accurate and current data available. Reports are prepared for subsidence and deformation surveys. Control maps are prepared for scour, construction, and aerial control surveys.

To research Geodetic Control, please go to http://www.ocgeomatics.com/landrecords/

OCRTN

The Orange County Real Time Network (OCRTN) consists of 10 continuously operating GPS reference stations (CGPS) located in and around Orange County. These CGPS stations are part of the California Spatial Reference System (CSRS) and the California Real Time Network (CRTN). OCRTN CGPS stations sample data at a 1 Hz interval (every second) and the raw data is streamed in real-time to a server located at the Geomatics office in Santa Ana. All sites contain GPS dual-frequency receivers with Geodetic choke ring antennas. This raw data along with generated RINEX files are archived for each site in 24-hour files and can be downloaded at the Scripps Orbit and Permanent Array Center. For specific epoch interval requests, please contact:

Charles Beal (714) 834-3499

At the same time, RTCM type 18, 19, 3, 22 messages are generated from each CGPS station and can be used for RTK surveying and are available to anyone at no cost. Users can access this data via the Internet using TCP/IP by using a wireless data modem. These data streams can be accessed from two different locations, the Geomatics office and the CSRC office. IP addresses and port assignments can be found by downloading the Procedures for Using OCRTN document.

Click here to view an image of the Orange County Real Time Network.

Click here to go to the CSRC California Real Time Network (CRTN).

For more information or if you would like to receive information and notifications related to OCRTN, please send your email address to: Charles Beal

OCRTN Related Downloadable Documents - PDF files unless otherwise noted.

• Procedures for Using OCRTN
• OCRTN Components
• OCRTN POB Article August 2003
• OCRTN for CSRC Real-Time Symposium

Santa Ana River Calibration Base Line

The Santa Ana River Calibration Base Line was established in 1972 and is maintained by the Orange County Surveyor. It is located on the east bank of the Santa Ana River between Lincoln Avenue and Ball Road, in the city of Orange. It was designed for calibration of EDM equipment and is available to the private and public companies and agencies without charge.

In cooperation with the National Geodetic Survey (NGS), the SAR calibration base line is now part of the NGS EDMI Calibration Base Lines. The base line was re-measured in June 2006 by the G/LIS Geodetic Unit after being trained by the NGS in using their equipment and procedures.

Click here to download the "Santa Ana River Calibration Base Line" form.

Geodetic Related Downloadable Documents - PDF files unless otherwise noted.

• Procedures for Establishing the Mean High Water Line Boundaries
• Orange County Tide Planes and Tidal Datum Relationships
• U.S. Tidal Datum Relationships and Marine Boundaries
• Santa Ana River Calibration Base Line Form

Control Networks   Horizontal:The current horizontal control datum is the CCS83, zone VI, 1991.35 epoch adjustment. This network consists of approximately 2700 stations located on a ½ mile grid throughout the developed areas within the county. The majority of these stations have recorded cadastral references and all of them can be used to comply with the Ordinance 3809 Basis of Bearings requirement. Additional stations will be added in the future as areas become further developed.

Vertical: The two current vertical control datum's are the NAVD 88, OCS 1995 adjustment and the NGVD 29, OCS 1995 adjustment. This network consists of approximately 1700 benchmarks with a ½ mile spacing along the level lines throughout the county. Additional benchmarks will be added in the future as areas become further developed.

To research Geodetic Control, go to http://www.ocgeomatics.com/landrecords/

Datum and Epoch

Horizontal: Horizontal Control Points may have different coordinate values due to the datum and / or epoch date used. To avoid confusion, always state the datum and epoch as references when using GPS control points coordinate values.

Vertical: Benchmarks may have more than one height due to the datum, adjustments, and year leveled. To avoid confusion, always state the datum, adjustment, and year leveled as references when using benchmark elevation values.

Geodetic Control F.A.Q. - Frequently Asked Questions