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​ ODOT's VRS RTK Network

 

VRS and RTK 
VRS (Virtual Reference Station) is a system composed of hardware and software designed to facilitate real-time GPS/GNSS positioning based on a set of reference stations.  ODOT utilizes its CORS (Continuously Operating Reference Station) network to perform the role of the reference stations.  The VRS system relies on Trimble’s RTKNet software which is the operational component that generates a modeled solution.   One primary benefit of VRS is that you don’t need a separate GPS base station and someone to guard it in order to perform RTK positioning across the state.  Using VRS, the CORS network acts essentially as a continuous reference station within the entire network.  This allows RTK (Real Time Kinematic) positioning using a single (properly configured) rover in the field.


Applications
 
There are an endless number of potential applications that might benefit by using ODOT’s VRS to perform RTK positioning.  A few industries which have pursued VRS to date include surveying, construction, agricultural, and GIS.  Please contact us if you would like to test VRS for any specific applications.
 
 
Surveying
Construction
 
           
 Agricultural
GIS 
 
 

 

Compatible Equipment

There are multiple brands of GPS equipment that are compatible with ODOT’s VRS network including Trimble, Leica, Topcon, and others.  In general, most equipment that can navigate NTRIP can be utilized.  Please note that some GPS equipment not originally designed for use with VRS may now be compatible using third party software/equipment.
 
Datum/Reference Frame
 
Currently we are offering multiple Datum and Reference frame corrections as we transition from the NAD83 (CORS96) adjustment to the NAD83 (2011) horizontal adjustment. These reference frames/datums are determined by the mountpoint you select when logging into the network.
 
The CORS 96 horizontal component of the VRS network is based on the NAD83 (CORS96) reference frame; 2002.0 ephoch, as determined by the NGS (National Geodetic Survey).
 
To utilize this reference frame/datum, please choose one of the following mountpoints:
-ODOT_AG
-ODOT_CMR_PLUS
-ODOT_RTCM23
-ODOT_TRCMS
 
The NAD83 (2011) horizonatal component of the VRS network is based on the NAD83 (2011) reference frame; 2010.0 epoch, as determined by the NGS.
 
To utilize this reference frame/datum, please choose one of the following mountpoints:
-ODOT_NAD83(2011)_ODOT_AG
-ODOT_NAD83(2011)_CMR_PLUS
-ODOT_NAD83(2011)_RTCM23
-ODOT_NAD83(2011)_RTCM30
 
The vertical component for all mountpoints of the VRS network is based on NAVD88, as determined by NGS. 
VRS Revisions History
 
The VRS network is internally positioned from one CORS reference station to another with a high degree of accuracy.  The entire VRS network (i.e., all CORS stations within the VRS network) provide RTK coordinates relative to the nearest Ohio DOT CORS station.  The coordinates for the CORS station are periodically updated by NGS (National Geodetic Survey) and therefore updated for VRS use as well.  Any revisions to the CORS Station are recorded in the VRS Revisions History (below) due to the significance of this station within the network.   Specific high accuracy applications may be affected by the periodic change in coordinates of the CORS station.  Therefore, current subscribers of VRS will be notified if revisions to the coordinates of the CORS station are made. The only revision to the network has been the addition of NAD83 (2011) coordinates available through new mountpoints.
 
Data Formats
 
ODOT’s VRS network generates GPS data correction information in CMR+, RTCM 2.3, and RTCM 3.0 formats, as well as the ODOT_Ag corrections format that is CMR+ without GLONASS for older Legacy, GPS only units.
 

Accuracy

The accuracy of ODOT’s VRS has been found to be suitable for many applications. The user should perform their own testing to ensure the VRS will meet the needs of a specific application.  Individual accuracies using VRS are a function of many parameters including items such as the equipment, equipment settings, software, GPS/GNSS characteristics, environment, and the procedures being used.  All accuracies discussed here are with respect to the reference system, which is the ODOT CORS network in our case.  The CORS network is positioned by NGS for various reference frames.  See the Datum/Reference Frame section for the current datum/reference frame being used for ODOT’s VRS network.

Access to VRS

 
To obtain access to ODOT’s VRS network, please contact one of the following individuals at ODOT:    
 
Dave Beiter        614-275-1372    Dave.Beiter@dot.state.oh.us
Matt O'Bryan      614-466-7880    MOBryan@dot.state.oh.us
 
A user “login” and “password” will then be issued for VRS use.