WHEEL 5445732 - Caterpillar

GPS Levels of Position Accuracy
Illustration 1 g01297476
The four basic levels of GPS position accuracy include: (1) Autonomous (lowest precision) - 10 m (30 ft) to 15 m (50 ft): Standalone mode uses only one receiver. The resulting measurement has no repeatability and high variance. (2) DGPS (low to moderate precision) - 30 cm (12 in) to 100 cm (40 in): This mode uses a base station and a second receiver, or some other correction source. Examples of sources are land-based beacons or satellite broadcasts from satellites that are orbiting the earth. This differential measurement method results in a measurement with increased accuracy but low repeatability. (3) RTK Float (moderate precision) - 20 cm (8 in) to 100 cm (40 in): This mode uses a base station and a second receiver. Medium cost circuitry and additional measurement parameters result in a marginally repeatable signal with improved accuracy. (4) RTK Fixed (high precision) - 1 cm (0.4 inch) to 3 cm (1.2 inch): This mode uses a base station and a second receiver. High end circuitry and advanced measurement algorithms result in precise, repeatable position calculations.The CAESultra system for Earthmoving machines uses the Real-Time Kinematic (RTK) Fixed GPS method for computing positions.Real Time - The receiver position is calculated as the work is being performed.Kinematic - The exact position from the base station is calculated as a remote receiver moves from place to place.Determining the Location of the Positioning Module
To produce RTK positions, two GPS receivers are required. One receiver is known as the GPS base station receiver. The antenna for this receiver is in a known location and the exact coordinates of the antenna are fixed and recorded. The other GPS receiver is known as the rover. This receiver is located on the machine. The CAESultra system uses a rover that contains both the GPS receiver and the GPS antenna.
Illustration 2 g01297477
GPS and the CAESultra System (5) GPS satellite constellation (6) Base station radio antenna (7) Base station GPS antenna (8) Rover receiver mounted on roof of machine (9) Optional repeater radio (10) Data radioGPS Base Station
To produce RTK positions, a reference location or base station provides accurate positioning data. A GPS base station is typically installed at a fixed or semi-permanent location such as the roof of the site office. The coordinates (latitude, longitude, altitude) of the location are known to a high degree of accuracy.The GPS base station includes the following components:
GPS receiver
GPS antenna
Radio
Radio antenna
Connecting cables
Power supplyAs pictured in Illustration 2, the base station uses a dedicated radio for communicating position information over a wireless data link to the rover.Simultaneous observations (measurements) of the GPS signals are used from the satellite constellation (5). The signals originate from both the base station GPS antenna (7) and the rover GPS receiver that is mounted on the machine (8) .The base station uses a radio (6) for broadcasting the observed information across the data radio link to the radio on the machine (10). One base station can support an unlimited number