About the WSRN - Washington State Reference Network
The WSRN (Washington State Reference Network) is a regional cooperative of GPS reference stations and data that enables cost-saving solutions for public and private sectors in the fields of surveying, mapping, and other high accuracy location technology needs.

Participating entities include: The cities of Seattle, Renton, Bellingham, Kent, Auburn, and Shoreline; The counties of King, Snohomish, Skagit, Island, Jefferson, Thurston, and Pierce; Kitsap Public Utility District, the Washington State Department of Transportation and the Spatial Reference Center of Washington (SRCW); academic and scientific institutions and projects like the Pacific Northwest Geodetic Array (PANGA), Central Washington University, the University of Washington, and Renton Technical College.

Real-Time Networks, a timely solution
Though fairly new to the U.S., these types of networks have been very successful in Europe and Asia where networks span entire countries where utilization is spreading beyond surveying to mapping, utilities, emergency response, agriculture, forestry, public safety, transportation, machine control for construction, environmental, and scientific research.

Great examples of successful networks are SAPOS in Germany, the Jenoba and Nippon GPS Data Services in Japan, and the new statewide network hosted by the Ohio Department of Transportation.

Cost savings can be substantial. High accuracies at high speed: By following proper procedures, users can observe locations to centimeters in seconds. There are WSRN users who are quite willing to share their success in utilizing the system, and test accounts can be arranged.

The Role of Seattle Public Utilities
Seattle Public Utilities (SPU) serves as the central data processing host for the VRS network, and maintains key elements of a core network for internal SPU and city needs. The core network includes three SPU stations, and seven stations hosted by surrounding entities through signed agreements with SPU.

The network is scalable: through further agreements with other partners and members the network has expanded across a wider area of the Puget Sound Region and will expand across other regions of Washington state as opportunities arise

The Central Processing Center (CPC) provides central communications, data processing, correction distribution, integrity monitoring, support, GPS data file access, real-time and web-based services for WSRN members and subscribers. Many of the WSRN services are free and open to the public, with the exception of real-time network corrections, which is accessed by authenticated access accounts.

Members are contributors to the infrastructure of the expanded network, either as base station hosts, or financial contributors. Subscribers make their contribution to the cooperative, on a nominal cost recovery basis, in the form of annual subscriptions for service

SPU conducted an 18-month pilot to compare the use of these new tools with convention measurement technology methods. This not only provide a cost-benefit model for SPU's funding of the CPC, but tested feasibility of a network in under conditions specific to the region. The pilot was a great success, and pilot materials are available on request.

Conceptual Model of the WSRN (VRS Network)
The WSRN is comprised of a network of regional CORS (Continuously Operating Reference Stations connected via the Internet to a Central Processing Center (hosted by SPU). These CORS are essentially a high-end GPS receiver with a geodetic-grade antenna on a very stable mount. The CORS dual-frequency receivers can be from any number of manufacturers; there are already Trimble, Geotracer, and Leica receivers, the choice of each CORS host. These CORS are at physically secure locations with reliable sources of power and Internet communications. These stations are typically located at 20-50km intervals but can maintain effectiveness even if spaced up to 70km apart (or more as has been tested in Europe).

These stations transmit a stream of GPS observations (collected from up to 10 satellites each) simultaneously to the CPC. Users of the services may utilize static GPS data files from the CPC via Internet or enhanced GPS data corrections in real-time.

Central Processing Center (CPC)
The CPC is a collection of physical servers and software that provides static GPS files, real-time corrections, network monitoring, and administrative functions. The components are standard SPU servers, and the Trimble © GPSNet/RTKnet suite of software running on standard Windows operating systems.

Static Files. The CPC also generates the static GPS files and posts these to the WSRN web server, transmits specific data to scientific and academic research concerns via FTP, processes requests for custom time-period & rate static files, and can generate a 'Virtual' static file which also includes atmospheric and orbital modeling. The user may download static GPS data files for 'post-processing' along with their own field observation files to derived accurate locations.

Monitoring. The CPC collects the data streams from the CORS, monitors the stability, quality, and availability of the CORS and their resultant data elements. The user may also view all network monitoring files and reports via the web interface. This option is important, as the user must review network status in determining fitness for use of any individual network elements or data products. The CPC monitors the positional integrity of the network to the millimeter, atmospheric, orbital, multi-path interference, and communications anomalies and transmits alerts to the administrator and users. All user transactions and account histories are recorded in databases

Real-Time Corrections. The CPC provides a central portal for users to access both traditional Real-Time Kinematic GPS corrections from individual CORS, or the more enhanced Virtual reference Station (VRS) type of correction from multiple stations simultaneously. Access is via registered password protected accounts.

The user initiates a session from their own mobile field GPS unit (rover) by contacting the CPC via cellular data connection and chooses the style of correction desired. Network corrections can help offset certain types sources of error common to real-time GPS, like the atmospheric delays illustrated on the left. In the case of a VRS observation, the rover sends it's autonomous (rough) location to the CPC. The CPC then develops an atmospheric model from (up to) the nearest six CORS, and adds corrected orbital info (from federal sources on the web), develops a unique set of corrections for the users location then sends a corrected stream back to the rover.

These corrections are in industry standard formats of several types RTCM and CMR, useable by rovers produced by multiple manufacturers, and as the CPC software is on a maintenance/subscription model, newer industry standards will be implemented as they are approved by the respective international committees. The authentication protocol for secure access accounts is also an industry standard, implemented by most manufacturers, and more as has happened in Europe.

WSRN Development Timeline

• Regional entities implement conventional GPS for surveying and mapping in the late 80's and early 1990's
• GPS is utilized to establish base themes for city GIS - Joint Aerial Mapping Project 1993
• First regional reference stations are independently established by individual entities, like the city of Renton in the mid to late 90's. First SPU reference station established in conjunction with UW Geophysics and PANGA in 99
• Meeting of interested parties proposes Northwest Unified Base Station (NUBS) network in 98
• WSRN conceptually formed by Dave Riecken of Metro-King County, Bob Maconie of the city of Renton and Gavin Schrock of SPU in 2000
• Pilot Virtual Reference Station network (4 stations) established in cooperation with City of Renton and Kitsap PUD - Nov 2002. 2 King County stations added in early 2003.
• Pierce County CORS goes online in mid 2003, with real-time and web services.
• SPU approval of production network (10 stations) and funding - May 2004
• Core network launched (8 of 10 stations) - Aug 2004, members and partners begin use.
• Core network completed Dec 2004 - 10 Stations.
• Expanded network begins - 15 stations by April 2005, test period ends, first subscribers
• Development plan in conjunction with PANGA, SRCW, and WSDOT: 24 stations by years end 2005, 33 by years end 2006 covering and area from Centralia to the Canadian border, Olympic to Cascade mountains.
• Cooperation with parties proposing networks in Vancouver/Portland, Spokane, Tri-Cities, and Central Washington. Other parties continue to lobby for a proposed 80 station statewide network.

Outreach
The WSRN continues outreach to the user community and potential beneficiaries of such networks in our region and in other parts of the Pacific Northwest. It is hoped that the user forum will serve not only the WSRN users, but also all parties interested in real-time GPS. The WSRN holds user meetings to exchange tips, tricks, solutions, and ideas, and presents at industry conferences like the LSAW (Land Surveyors Association of Washington), ACSM, ASPRS, APWA, URISA and others by request. Materials and papers from these presentations are available on request. The WSRN has also presented to other regions interested in developing their own networks in other states and internationally, and have been published in industry periodicals.