ELBOW 0026240 - Caterpillar

Illustration 5 g01374212
GPS accuracy levels (1) Autonomous (2) DGPS (3) RTK Fixed (4) RTK Float (5) SBASThe method that is used for machine grade control in construction is the same as that used by surveyors for stakeout in construction. The method is called Real-Time Kinematic (RTK), GPS.In order to produce RTK positions two GPS receivers are required. One receiver is known as the GPS base station and is fixed in one place. The other GPS receiver is known as the rover. This receiver can be stationary or mobile.The base station communicates to the rover ('s) through a wireless data link using a data radio. Illustration 6 shows this setup.
Illustration 6 g01507075
GPS and the AccuGrade® System (1) GPS satellites (2) GPS base station and data radio (3) Repeater radio (optional) (4) Machine equipped with the AccuGrade SystemBoth GPS receivers make observations (measurements) of the GPS signals at the same time. The base station broadcasts the observed information together with the location and other information across the data radio link to the rover. The rover then combines the data from the base station together with its own data in order to compute a very accurate position relative to the base station.A single base station can support an unlimited number of rovers, provided the rovers are within about 20 km (12.4 miles) of the base station. Normally, the range of the data radio link is the more limiting factor. You can use radio repeaters in order to extend the radio coverage.In areas where the 900 MHz band is available, the TC900C or CR900 data radio is recommended. In areas where the 900 MHz band is not available, one of the following radios is recommended:
TC450 (450 Mhz)
TC2400 (2.4 Ghz)Low accuracy corrected GPS (SBAS)
If low accuracy GPS positions are adequate for the required site work, you can use Satellite-Based Augmentation System (SBAS) error corrections. SBAS corrected systems do not require additional site infrastructure.Satellite-Based Augmentation Systems are free-to-air GPS correction services. SBAS networks consist of ground stations that are set at known positions around the world, and geo-stationary satellites that maintain a fixed position above the Earth. The ground stations receive GPS signals from all GPS satellites in view. The GPS data is then sent to a master control site, which then transmits GPS corrections to the geostationary satellites. These satellites broadcast the information to all SBAS enabled GPS receivers.The following SBAS networks are currently available:WAAS - Wide Area Augmentation System (United States)EGNOS - European Geostationary Navigation Overlay Service (Europe)MSAS - Multi-Functional Satellite Augmentation System (Japan)GPS receivers use a GPS receiver configuration file (.cfg) to convert from WGS84 coordinates to the site coordinate system. High accuracy (RTK) GPS systems use a configuration file generated from the site calibration. Inaccuracies in the entered position of the base station for the site calibration will result in a shift of the site coordinate system away from the local circuit coordinate system. When this configuration file is used by a GPS receiver using RTK, the shift is not exposed, as