EDGE-CUTTING 5332647 - Caterpillar

The Global Positioning System (GPS)
GPS is a system of satellites that orbit the earth two times per day at very high altitudes. The radius of the orbit is approximately 26600 km (16528 miles). GPS was set up by the government of the United States. GPS provides precise timing and positioning to users anywhere at no charge for 24 hours per day.Newer GPS receivers will be able to also receive data from the Global Navigation Satellite System (GLONASS). GLONASS consists of 21 satellites in 3 orbital planes, with 3 on-orbit spares. The three orbital planes are separated 120 degrees, and the satellites within the same orbit plane by 45 degrees. Each satellite completes an orbit in approximately 11 hours 15 minutes. This allows more GPS satellites to used to for the solution.In very general terms, a GPS Receiver computes a position that is based on radio signals that are received from several different satellites. The satellites have highly reliable clocks, so the timing of these satellite signals is very accurate. The GPS Receiver calculates the relative distance to each of the satellites. This calculation is based on the travel time of the signal and the speed of light (speed of the signal). The receiver then uses these distances in order to calculate the receiver's location on earth.As a broadcast only radio system, GPS supports an unlimited number of users. The broadcast frequencies penetrate clouds, rain, and snow. GPS can also accurately guide operations in fog or dust, as well as at night. There are different levels of precision and accuracy that are available from GPS. There are four basic levels of GPS position accuracy."Autonomous" - 10 m (30 ft) to 15 m (50 ft)"SBAS" - 1 (3.3 ft) to 2 (6.6 ft)"DGPS" - 0.3 m (1.0 ft) to 1.0 m (3.0 ft)"RTK Float" - 0.2 m (0.7 ft) to 1.0 m (3.0 ft)"RTK Fixed" - .02 m (.07 ft) to .03 m (.10 ft)Illustration 1 shows the GPS levels of position accuracy.
Illustration 1 g01374212
GPS levels of position accuracy (1) "Autonomous" (2) "DGPS" (3) "RTK Fixed" (4) "RTK Float" (5) "SBAS" The 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. This receiver is fixed in one place. The other GPS receiver is known as the "rover". This receiver is mounted on the machine.The base station communicates to the "rovers" through a wireless data link with a radio. Illustration 2 shows this setup.Both the GPS base station and the GPS "rover" 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 "rover" and the base station in order to