EDGE-SEGMENT 4709306 - Caterpillar

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 the relative positions of points on the site are still accurately known, and the accuracy of RTK positioning is unaffected. However, if the same configuration file is used by a GPS receiver using SBAS corrections, the shift in the site coordinate system away from the local circuit is exposed, and results in additional positioning errors.To avoid additional errors, do one of the following:
Make sure the base station antenna position used for the RTK site calibration is accurate to within about 1 m (3.3 ft). This accuracy can be achieved via traditional surveying methods or long autonomous GPS occupations. Speak to your site surveyor for more information.
Use a configuration file generated by the AccuGrade Office software using the local circuit coordinate system, instead of the configuration file produced by the site calibration.GPS Site Calibration
Note: A poor quality GPS site calibration will result in poor quality guidance information from the AccuGrade Grade Control System.A GPS site calibration is a mathematical relationship between a grid coordinate system (northing, easting, and elevation) of a project and the GPS coordinate system (latitude, longitude, and ellipsoidal height - also known as WGS84 coordinates ).This relationship is determined by using GPS to measure points with known grid coordinates, and then calculating the calibration parameters. A surveying or civil engineering company should be employed to establish the control points around a site. Make sure that you locate the control points where they will not be destroyed during construction. Five or more control points located at, or near, the corners and center of the project will normally give good results.Note: If you employ a GPS surveyor to create the GPS site calibration, make sure that you clearly specify the requirements. Caterpillar