GPS

Global Positioning System (GPS) equipment utilize a constellation of 24 satellites placed into orbit by the U.S. Department of Defense. These satellites are used as reference points to calculate positions on the planet as precise as a meter, and with advanced GPS tools, better than a centimeter.

WESTON often uses one or more of the following GPS methodologies to provide real-time geographical data in the field or at a job site:

• Autonomous GPS Collection involves using simple GPS equipment with no additional correction information. Two Autonomous GPS units used by WESTON are the Garmin III+ GPS Receiver and the Teletype PCI PCS Card for Portable Digital Assistants (PDAs).

• Differential GPS (DGPS) Collection provides a more accurate method and involves the collection of data from a base station and a GPS rover. DGPS units used at WESTON include the Trimble Pro-XR and Pro-XRS.

• Real-Time Kinematic (RTK) Survey achieves centimeter accuracies. Baseline calculations are made from a base station on a known benchmark, such as a National Geodetic Survey (NGS) monument. RTK GPS units used by WESTON include the Trimble RTK 5700.