In 2012, the National Geodetic Survey (NGS) completed their National Adjustment to the NGS Continuously Operating Reference Station (CORS) network to continue to improve the National Spatial Reference System (NSRS). The NSRS is the official U.S. reference system for latitude, longitude, height, scale, gravity, and orientation.
To maintain an accurate tie between the Trimble VRS Now network in the U.S. and the NSRS, the NGS CORS network, and other modern reference frames, Trimble Positioning Services will apply a network adjustment on February 21, 2015. The shifts observed between the current and future coordinates of the network stations range from millimeters up to several centimeters. We appreciate your assistance in preparing and planning for this change as we modernize the VRS Now network to better serve our users.
Trimble VRS Now Network Adjustment
The VRS Now US network reference frame will be changed from NAD83(CORS96) Epoch 2002.00 to NAD83(2011) Epoch 2010.00. In addition to the network adjustment, NGS has developed a hybrid geoid model, GEOID12A, for use with NAD83(2011) Epoch 2010.00 ellipsoid heights.
The VRS Now US network adjustment was performed by geodesists at Trimble and independently verified by a third party. After extensive verification and testing, the network adjustment will be deployed in early 2015. Â
 The maintenance period to implement the network adjustment is scheduled to start on February 21 at 10:00 PM (MST) and is expected to last for approximately 90 minutes. During this time, the VRS Now US network will not be available. After this maintenance period, the VRS Now US network will broadcast corrections in the NAD83(2011) Epoch 2010.00 datum on existing mountpoints.
Managing the Transition
For projects containing positions or control established in NAD83(CORS96), either a transformation or site calibration will need to be performed. For site calibrations, site managers should make sure that existing control is available and accurate prior to the change on February 21.
To help ease the transition for customers who have ongoing projects and need to continue working in NAD83(CORS96) Epoch 2002.00, a temporary solution will be available: corrections will continue to be broadcasted in NAD83(CORS96), but on new mountpoints. The new mountpoints will be available prior to the network transition date to help minimize downtime while reconfiguring mountpoints. This temporary overlap of corrections in NAD83(CORS96) will be available from February 11, 2015 until May 20, 2015; please contact the VRS Now Customer Care team for more information about using the temporary NAD83(CORS96) mountpoints.
For Additional Information
Additional information about the NGS National Adjustment of 2011 can be found on their website at http://www.ngs.noaa.gov/web/surveys/NA2011/
NGS has also created a transformation tool, available on their website at https://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml
More information about GEOID12A can be found at http://www.ngs.noaa.gov/GEOID/GEOID12A/GEOID12A_data.shtml
If you have any questions, please contact our VRS Now Customer Care team at +1-877-552-6996 or via email at am_corrections@trimble.com .
for more information http://www.trimble.com/positioning-services/vrs-now.aspx