Development of a GPS Active Control Point Station

The Geodetic Survey Division, Canada Centre for Surveying, has embarked on the implementation of the Active Control System, a project to establish a nationwide network of automated Global Positioning System (GPS) tracking stations, or active control points (ACPs). Benefits from such a network include improved integrity, precision and economics of both differential static and kinematic positioning applications using GPS, and independent orbit determination and refinement. A prototype ACP station has been constructed to test the concept. The station consists of a Texas Instruments TI 4100 receiver interfaced to a Micro VAX II computer. Meteorological sensors and a dedicated communications, line are also interfaced to the computer. The station is capable of unattended operation, automatic satellite tracking, and the acquisition, decoding, validation and transmission of data to the remote Master Active Control Station (MACS). The ACP station can be interrogated from the MACS to monitor or modify its operations. In this paper we describe the development of the prototype ACP station and its capabilities, and the potential for a network of such stations to revolutionize the practice of surveying.