Pennsylvania GPS - CORS Project
by
Eduardo Fernandez-Falcon
During the last decade, the impact of GPS (Global Positioning System) in positioning and navigation have been tremendous. GPS is now an affordable and readily available way of determining high accuracy positions. Surveyors benefit from the use of GPS and will continue to do so in search for cost reduction and increasing accuracy for their surveys.
In very basic terms, GPS position determinations can be carried out in absolute or relative forms. Absolute determinations, also called point positioning, are conducted using a single GPS receiver to obtain the (X,Y,Z) coordinates of a point in a specific coordinate system. Relative determinations (differential GPS) are carried out by using 2 or more GPS receivers and computing the increments in the coordinates (DX,DY,DZ) between them. Relative determinations are much more accurate than point positioning. Also, the absolute position of a point in a specific reference system can be computed if one of the GPS receivers used in relative positioning is setup in a benchmark with known coordinates.
These are the principles behind the development of the Continuously Operating Reference Station (CORS) Network. The idea is to continuously collect GPS data, on highly stable stations of known coordinates in the National Spatial Reference System (NSRS), currently NAD 83 (North American Datum of 1983), and make that data available to the public for GPS differential computation. As a result, users will be able to determine their positions with high accuracy in relation to the NSRS by using a single GPS receiver (capable of differential measuring) and processing the data available from the CORS network.
The CORS network is designed and coordinated by the National Geodetic Survey (NGS) and when complete, will have between 150 and 200 stations covering the US. The accuracies of the baselines vectors between CORS stations run between 1 and 3 cm in horizontal and between 2 and 5 cm in vertical directions. In the future, it is expected that those values will drop up to 2 or 3 millimeters in both vertical and horizontal directions.
During 1995, the Pennsylvania Department of Transportation (PennDOT) decided to participate in the CORS project seeking to fulfill its mandate to provide geodetic control for the Commonwealth of Pennsylvania. After initial consultations, PennDOT, represented by Mr. John Ewell and Mr. Emerson "Butch" Bornman coordinated a meeting with the NGS, represented by Mr. William Strange, and Penn State University (Surveying Engineering Program), represented by Mr. Eduardo Fernandez-Falcon late in 1995. As a result of that meeting, PennDOT agreed to provide the hardware and software required for the setting of 3 CORS stations across Pennsylvania; Penn State University made its campuses, internet installations and GPS expertise available for the project, while NGS agreed to advice and coordinate at Federal level.
During 1996, installation details were worked-out, legal agreements were signed and technical problems were solved. On December 1996, two GPS-CORS stations were setup. The first one, named WIL1, in northeast Pennsylvania (Penn State University,Wilkes-Barre Campus). The second one, named PIT1, in the southwest (Penn State University, New Kensington Campus). Plans are currently under way to setup the third station in State College (Central PA) during January 1997. At this time (late December 1996), the stations are being tested and technical adjustments are being made. Data from these stations will be publicized as soon as the stations become stable and completely reliable (sometime in early January 1997). The three stations mentioned above will provide sufficient cover for the whole Commonwealth.
The GPS-CORS project in Pennsylvania is an example of cooperation between State and Federal government and the University. In times in which every institution is minimizing their budgets, these organizations and their personnel managed to work together to make a new and valuable service available to the public. Numerous people have helped to make this project a reality. Besides the project coordinators from PennDOT (Mr. John Ewell and Mr. Emerson Bornman); NGS (Mr. William Strange) and Penn State University (Mr. Eduardo Fernandez-Falcon); Mr.Michael Cline(NGS-New Jersey Geodetic Advisor) and Mr. Brian Naberezny (Student at the PSU-Surveying Engineering Program) have been instrumental in the setting of the GPS stations. Administrative and technical personnel of both institutions have also play important roles in "getting the job done." Our appreciation goes to all of them.
The following are some of the photographs taken at Penn State, Wilkes-Barre campus, home of the Surveying Engineering Program, while setting the GPS-CORS named WIL1.
These pictures show the Hayfield House at Penn State University,Wilkes-Barre campus. The arrow
marks the location of the GPS antenna for the CORS
named: WIL1.
The photograph on the left shows Mr. Michael
Cline, New Jersey Geodetic Advisor (NGS) and Mr. Emerson "Butch"
Bornman (PennDOT)
setting up the antenna for WIL1. On the right, there is a picture
of the horizon as viewed from the antenna's position.
This photograph depicts "Butch" Bornman and Brian Naberezny (PSU Surveying Student) setting up the portable computer that receives the GPS data from the WIL1 station and serves it to the Internet after processing and storage.
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