GPS + GLONASS for Precision
South Carolina’s GNS Virtual Reference Network
With Russia’s GLONASS undergoing a rapid rebuilding and modernization process, GNSS receiver manufacturers and users have found more reason to consider exploiting the larger number of satellite signals available in a mixed constellation. South Carolina’s Geodetic Survey (SCGS) has put the state on the map as the first to implement a “virtual” reference station network that provides precise real-time differential corrections to both GPS and GLONASS signals. The chief of SCGS and the VRS project manager describe how their agency did it and who’s benefiting from the new statewide service.
The SC Geodetic Survey (SCGS) has combined the technologies of the GPS, GLONASS, cellular communications and high-speed server networks to provide centimeter-level accuracy in real-time for surveying, mapping, and engineering applications.
Named the SC Virtual Reference Station (VRS*) Network, the system is composed of 45 global navigation satellite system (GNSS) receivers installed statewide and connected by high-speed Internet to servers in the state capital, Columbia. Users connect in the field via cellular digital data communications to access the servers and obtain near real-time custom corrections to position objects or automate vehicle operations.
The South Carolina Department of Transportation has partnered with the SCGS with the intention of using the VRS for machine control to automate highway construction. South Carolina is the only state in the nation to use this technology to include the Russian GLONASS satellites as well as GPS satellites for a more robust solution.
Important to the implementation of the VRS is the provision of a common and consistent connection to the North American Datum NAD83 (2007) via the South Carolina State Plane Coordinate System. All coordinates produced through the use of VRS can be directly tied to NAD83 (2007). Surveyors and engineers will no longer need to be concerned about datum issues and coordinate conversions.
This article will describe how SCGS, which operates within the state Budget & Control Board’s Office of Research and Statistics, designed, implemented, tested, and operates the GNSS VRS network today.
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ManufacturersThe South Carolina VRS Network base station receivers are Trimble NetR5 and use Zephyr Geodetic Model 2 antennas from Trimble Navigation Ltd., Sunnyvale, California USA. Trimble R8 GNSS receivers with built-in Zephyr-style antennas are used for field operations. The rovers are controlled by a Trimble Ranger (TSC2) data collector, which has a Bluetooth wireless connectivity to the R8 and cell phone.
The VRS network servers based in Columbia are PowerEdge 1955 Blade Servers from Dell Computer Corporation, Austin, Texas USA. Each virtual server was created using virtualization software from VMware Inc., Palo Alto, California USA, a wholly-owned subsidiary of EMC Corporation, and operates with the Microsoft Server 2003 SP2 operating system from Microsoft Corporation, Redmond, Washington USA. Two of the three virtual servers host the Trimble RTKNet kernel of the Trimble GPSNet software. Data from the reference stations enters the virtual infrastructure through a firewall using Cisco PIX Device Manager 3.0 from Cisco Systems, Inc., San Jose, California USA. SCGS VRS users gain access to the VRS network via a Microsoft Access database.
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