GPS Technology—WisCORS & the VRS

This year a tremendous tool has become available to those of us in Southeastern Wisconsin. This new technology is a result of many years of planning, and cooperation between equipment vendors, private corporations, educational institutions, and the Wisconsin Department of Transportation. Yaggy Colby is proud to be one of the inaugural users of this technology.

The Wisconsin Department of Transportation (WisDOT) Geodetic Survey Unit is developing a statewide Global Positioning System (GPS) reference station network. The Wisconsin Continuously Operating Reference Stations (WISCORS) Network consists of permanent GPS sites, which provide real-time correctors to mobile users. Mobile users that are properly equipped to take advantage of these correctors can survey real-time in the field to the 2-cm accuracy level.

The first phase of this network has been completed which established 25 permanent CORS in Wisconsin operating east of a line from Marinette to Shawano to Fond du Lac to Madison to Janesville. Corrections are provided in real-time via data packet transmission over cell phones.

Benefits of the CORS Network

· Eliminates the need and cost for another GPS receiver, which acts as a base.

· Eliminates the resource time associated with equipment setup at the base site.

· Enhances security of equipment with no unmanned base sitting miles away from the operator.

· Greatly enhances consistency of coordinate determination.

· Eliminates the need for permanent monumentation on a local level.

· Reliability and redundancy is ensured.

It is important to remember that all standard GPS practices must continue to be utilized just as if we were not using this system. This means that although the surveyor can get out of the truck and start collecting data with the GPS, they still must perform a calibration, and complete their vertical checks. One way to visualize the way this system works is to think of the VRS (Virtual Reference Station) as the GPS base. All functions the base would normally do during a GPS survey, the VRS is now doing. We must still give the software the fixed points on the ground to correlate the information from the VRS to actual survey work.

Calibrations are conducted with points of known coordinates on the ground. The calibration to 4 horizontal points is less than a 30-minute process today. In Southeastern Wisconsin many control monuments can be driven to, which makes calibration easy. The field surveyor can drive to a point, occupy that point for 3 minutes, and then drive to the next point. After this has been completed the survey work can begin.

The VRS system allows survey field crews to conduct data collection and staking in areas that would have been very difficult previously. In addition to opening up additional locations to conduct surveys, we are also able to do so in a highly efficient manner, saving clients money. We are using the VRS to provide surveying services in areas that would have formerly been cost prohibitive, and providing those services in a highly efficient manner.

The CORS/VRS system provides a tremendous advantage to our surveyors and clients. It saves equipment setup time, long complicated traverses, protects our assets, and offers clients a rapid turnaround of data at a reasonable cost. We have doubled our GPS capabilities to ensure that this tool is available when needed. If you have any questions, or are interested in finding out if GPS is right for your next job, please do not hesitate to contact me at davidb@yaggy.com.