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Oregon Real-Time GNSS Network Coordinates

Datum Realization

CURRENT DATUM REALIZATION
 
 
SUPERSEDED DATUM REALIZATION
 
 
The Oregon DOT Geometronics Unit intends to keep the Oregon Real-time GNSS Network (ORGN) aligned to the National Geodetic Survey (NGS) National Spatial Reference System (NSRS) to help surveying, mapping, and other professionals determine positional coordinates that are compatible with coordinates derived by others.  This use of a common coordinate base allows project coordinates to be exchanged freely and ensures projects match up on the ground, thus saving time, money, and possibly costly mistakes by geospatial professionals.
 
From its startup in 2006 until 8 March 2013, the datum realization for the Oregon Real-time GNSS Network was NAD 83(CORS96) epoch 2002.00, the same realization that was being used by the NGS for the National Spatial Reference System and all its active station products, i.e., NGS Continuously Operating Reference Stations (CORS) and Online Positioning User Service (OPUS).
 
In 2012, the National Geodetic Survey transitioned the National Spatial Reference System to a new datum realization: NAD 83(2011) epoch 2010.00.   All NGS products, including the NGS CORS, NGS OPUS, and positions of passive marks are now aligned to NAD 83(2011) epoch 2010.00.  For in depth information on how the NGS computed the new positions, see the NGS CORS Coordinates web page.  This change of NGS CORS positions reflects 8 years of plate movement from 2002 to 2010.
 
In order to align the ORGN with the new datum realization for the NGS National Spatial Reference System, the Oregon DOT Geometronics Unit transitioned the Oregon Real-time GNSS Network to the NAD 83(2011) epoch 2010.00 datum realization on 8 March 2013
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This is Not a Datum Change

Although the geographic coordinates of each ORGN site changed, the change from NAD 83(CORS96) epoch 2002.00 to NAD 83(2011) epoch 2010.00 is not a datum change; rather, it is a new realization of the NAD 83 datum using the same reference ellipsoid (GRS80) with the same origin, orientation, and scale as all other realizations of NAD 83. 
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Magnitude of Coordinate Changes

The magnitude of coordinate changes for ORGN sites varies throughout the state.  Horizontal coordinates change from as little as 2 centimeters in eastern Oregon to as much as 13 centimeters on the Oregon Coast.  Vertical coordinates change from less than a millimeter up to 3 centimeters.  The differences in magnitude throughout the state illustrate crustal motion over time.

 

 

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How Station Coordinates are Computed

To compute the superseded NAD 83(CORS96) epoch 2002.00 coordinates for ORGN stations, the Oregon DOT Geometronics Unit, after consultation with NGS, submitted 22 days of 24-hour RINEX files for each ORGN station to NGS OPUS-Static.  The resulting OPUS coordinates were statistically analyzed at the 99% confidence level. 
 
To compute the new NAD 83(2011) epoch 2010.00 coordinates for ORGN stations, ODOT Geometronics closely followed recommendations in the NGS draft “Guidelines for Real Time GNSS Networks”, v.2.0, March 2011.  Mark Armstrong, NGS State Geodetic Advisor for the State of Oregon, was the lead author in developing the ODOT “Guidelines for Positioning the Oregon Real Time Network with NGS Spatial Reference System Validation”.   The ODOT Guidelines closely follow NGS guidelines for computing coordinates for regional real time GNSS networks.  ODOT continues to work closely with NGS as they develop their policy and procedures for helping regional GNSS networks align to the National Spatial Reference System.
 
Elements of the plan for ORGN coordinate computation detailed in the ODOT “Guidelines for Positioning the Oregon Real Time Network with NGS Spatial Reference System Validation” include:
 
·          Processing 5 days (120 hours) of data for each ORGN station. We chose data that was collected during a period of high barometric pressure over the entire state: late September 2011.
 
·          Least squares adjustment of the data using NGS OPUS-Projects
 
·          Fixing, in our least squares adjustment, NGS CORS sites in Oregon and in surrounding states, that have “computed velocities”, that is, those NGS CORS sites with more than 2 ½ years of data used to compute site velocities.
 
·          Floating, in our least squares adjustment, those NGS CORS sites that only have “modeled velocities”.  These are CORS sites for which NGS had less than 2 ½ years of data.
 
·          Striving to work with adjacent real time GNSS networks, especially the Washington State Reference Network, to ensure coordinate compatibility between networks.
 
Note: The ODOT-adopted positions for stations in the ORGN may vary slightly from the NGS-adopted CORS position for our partner stations that also NGS CORS sites.  This is because the NGS has acknowledged that regional real-time GNSS networks such as the ORGN may require tighter internal consistency than the NGS policy provides for.  The NGS draft “Guidelines for Real Time GNSS Networks”, v.2.0, March 2011, state that "For the sake of internal network consistency, the RTN administrator may want to adopt his/her adjusted values for the CORS coordinates rather than use the NGS-adopted values."
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ORGN Products After Transition

ORGN PRODUCTS AFTER THE TRANSITION TO NAD 83(2011) epoch 2010.00


Starting at Noon, Pacific Standard Time, 8 March 2013, real-time correctors from the ORGN are referenced to NAD 83(2011) epoch 2010.00, latitude, longitude, and ellipsoid heights.

The ellipsoid heights sent out in ORGN real-time correctors are reduced from the antenna phase center to the antenna reference point (ARP).  The antenna reference point (ARP) is the physical point on the antenna, often the middle bottom of the antenna mount, to which all antenna calibrations are referenced.  In their rovers, ORGN users should configure the base receiver as UNKNOWN and configure the base antenna as NULLADVANTENNA, null, or none.  (Choices will vary between manufacturers, so please consult your vendor on how to configure your rover.  Your rover must be using the latest IGS08 absolute antenna model which should be a choice on your data collector.)
 
Also starting at Noon, Pacific Standard Time, 8 March 2013, RINEX files from ODOT-owned GNSS sensors have the NAD 83(2011) epoch 2010.00 coordinates embedded into the RINEX file; however, be aware that many of our ORGN stations are owned and operated by our partners, and our partner’s RINEX files may be referenced to a different datum or a datum realization than NAD 83(2011) epoch 2010.00.  
 
If you are post processing using RINEX files and want to align your project to NAD 83(2011) epoch 2010.00, you may use any RINEX files from ODOT or our partners, but when you fix control in your adjustments, use the ORGN NAD 83(2011) epoch 2010.00 coordinates
 
If you are post processing using RINEX files and want to align your project to NAD 83(CORS96) epoch 2002.00, you may use any RINEX files from ODOT or our partners, but when you fix control in your adjustments, use the superseded NAD 83(CORS96) epoch 2002.00 coordinates for the active ORGN stations.
 
Do not mix coordinates referenced to different datums or different datum realizations in the same project.
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Absolute Antenna Calibrations

IGS08 ABSOLUTE GNSS ANTENNA CALIBRATIONS


ORGN users should only use IGS08 Absolute Antenna Calibrations when processing data with ORGN or NGS CORS coordinates referenced to NAD 83(2011) epoch 2010.00.  IGS08 Absolute Antenna Calibrations are now the default value available for download on the NGS Antenna Calibrations web page.  Consult your GNSS vendor to ensure you are using IGS08 antenna calibrations in your rover and your post processing software when using coordinates referenced to NAD 83(2011) epoch 2010.00.

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GEOID Models

ORGN users should only use the NGS GEOID12A geoid model when using ORGN real time-correctors referenced to NAD 83(2011) epoch 2010.00 or when post processing when using coordinates referenced to NAD 83(2011) epoch 2010.00.  The GEOID12A model is intended to transform between NAD 83(2011) epoch 2010.00 ellipsoid heights and NAVD88 orthometric heights.
 
ORGN users post processing when using coordinates referenced to NAD 83(CORS96) epoch 2002.00 should use either the NGS GEOID03 or NGS GEOID09 geoid models.
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Agricultural Users of ORGN

Agricultural users in eastern Oregon are the least affected by the change to ORGN coordinates.  Positions on the ground may only change 1 inch or so, which may not require updating your land coordinate system.  Agricultural users on the Oregon coast may or may not want to make changes depending how they use their GNSS system.  Updating your land coordinate system may be accomplished similarly to how surveyors will update their project coordinates as outlined below.
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Surveying/Engineering Projects

(always document the datum realization of your projects in the project metadata.)

 

1.  Starting a New Project in NAD 83(2011) epoch 2010.00
 
Just start surveying using the ORGN real-time correctors which are referenced to NAD 83(2011) epoch 2010.00.    When post-processing, use the ORGN NAD 83(2011) epoch 2010.00 coordinates.
 
Use IGS08 Absolute Antenna Calibrations and GEOID12A.
 
2.  Continuing an Existing NAD 83(CORS96) epoch 2002.00 Project in NAD 83(CORS96) epoch 2002.00
 
Perform a localization/calibration/transformation on your project after occupying your project control points with GNSS while receiving ORGN RT correctors referenced to NAD 83(2011) epoch 2010.00.
 
 
Or, alternatively
 
Set up your own local RTK base station and input the superseded NAD 83(CORS96) epoch 2002.00 ORGN coordinates in to the base; then broadcast RT correctors to your rover in NAD 83(CORS96) epoch 2002.00.
 
In both alternatives above, use the superseded NAD 83(CORS96) epoch 2002.00 ORGN coordinatesfor post processing and continue to use GEOID03 or GEOID09.
 
3.  Transitioning an Existing NAD 83(CORS96) epoch 2002.00 Project to NAD 83(2011) epoch 2010.00
 
Perform a localization/calibration/transformation on your project after occupying your project control points with GNSS while receiving ORGN RT correctors referenced to NAD 83(2011) epoch 2010.00, but hold the new NAD 83(2011) epoch 2010.00 ORGN coordinates for your localization.
 
Or, alternatively
 
Reprocess your static data: perform a new network adjustment fixing the new NAD 83(2011) epoch 2010.00 ORGN coordinates on your control stations.
 
In both alternatives above, use GEOID12A
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ORGN Check-In Survey Marks

The National Geodetic Survey (NGS) has recognized that regional Real Time GNSS Networks (RTNs), such as the Oregon Real-time GNSS Network, will be one of the primary methods for GNSS users to access (and keep their projects aligned) to the NGS National Spatial Reference System.  Thus, the NGS recommends that high stability fiducial marks (trustworthy check-in marks) be constructed within the area covered by an RTN.  RTN users can test their rovers at these marks to compare the results from the RTN real-time correctors with published values for the same mark.
 
Please see our ORGN Check-In Survey Mark web page for information on how you can use and/or establish published survey marks to check your ORGN real-time correctors.
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ORGN Webinar

On 4 March 2013, Ken Bays, Lead Geodetic Surveyor for Oregon DOT, and Mark Armstrong, NGS State Geodetic Advisor for Oregon, presented a webinar entitled ORGN 2011 about the transition of the ORGN coordinates from NAD 83(CORS96) epoch 2002.00 to NAD 83(2011) epoch 2010.00.  Their presentations from that webinar are available here.
 
·          Ken Bays’ presentation
 
·          Mark Armstrong’s presentation
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