Accuracy standards for tracking device positioning techniques

The Federal Geodetic Control Committee (FGCC) has written provisional accuracy standards for GPS relative positioning techniques. The older standards of first, second, and third order are classified under the group C in the new scheme. In the past, the cost of achieving first-order accuracy was considered beyond the reach of most conventional surveyors. Besides, surveyors often said that such results were far in excess of their needs anyway. The burden of the equipment, techniques, and planning that is required to reach its 2σ relative error ratio of 1 part in 100,000 was something most surveyors were happy to leave to government agencies. But the FGCC’s proposed new standards of B, A, and AA are respectively 10, 100, and 1000 times more accurate than the old first-order. The attainment of these accuracies does not require corresponding 10-, 100-, and 1000-fold increases in equipment, training, personnel, or effort. They are now well within the reach of private GPS surveyors both economically and technically.

Along with mark setting information, the type of monument and the history of mark recovery, the NGS data sheets provide a valuable to-reach description. It begins with the general location of the station. Then starting at a well-known location, the route is described with right and left turns, directions, road names, and the distance traveled along each leg in kilometers. When the mark is reached the monument is described and horizontal and vertical ties are shown. Finally, there may be notes about obstructions to GPS Tracking Device visibility, and so forth.

The requirement to occupy physical geodetic monuments in the field can be obviated by downloading the tracking data available online from appropriate continuously operating reference stations (CORS) where their density is sufficient. These stations, also known as Active Stations, comprise fiducial networks that support a variety of GPS applications. While they are frequently administered by governmental organizations, some are managed by public–private organizations and some are commercial ventures. The most straightforward benefit of CORS is the user’s ability to do relative positioning without operating his own base station by depending on that role being fulfilled by the network’s reference stations.

While CORS can be configured to support differential GPS (electronic tracker ) and realtime kinematic (RTK) applications, as in Real-Time Networks, most networks constantly collect GPS tracking data from known positions and archive the observations for subsequent download by users from the Internet. In many instances the original impetus of a network of CORS was geodynamic monitoring as illustrated by the GEONET established by the Geographical Survey Institute (GSI) in Japan after the Kobe earthquake. Networks that support the monitoring of the International Terrestrial Reference System (ITRS) have been created around the world by the International GNSS Service (IGS), which is a service of the International Association of Geodesy and the Federation of Astronomical and Geophysical Data Analysis Services originally established in 1993. And the Southern California Integrated GPS Network (SCIGN) is a network run by a government–university partnership.

Despite the original motivation for the establishment of a CORS network, the result has been a boon for high-accuracy electronic tracking device positioning. The data collected by these networks is quite valuable to GPS tracker surveyors around the world. Surveyors in the United States can take advantage of the CORS network administered by the National Geodetic Survey, NGS. The continental NGS system is has two components, the Cooperative CORS and the National CORS. Together they comprise a network of hundreds of stations which constantly log dual-frequency GPS data and make the data available in the receiver independent exchange format (RINEX) format.