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GNSS Positioning for Machine Control: More Satellites - Higher Precision?

The most common method to position machines on construction sites is the usage of GNSS (Global Navigation Satellite System) positioning signals. This technology is integrated into construction equipment like: dozers, graders, excavators, paving equipment, agricultural harvesters, and tractors. With the use of this technology, productivity, efficiency, and reliability increase significantly. MOBA, for example, only offers for their Machine and Grade Control Systems receivers with GNSS capability. This means using positioning signals from the American GPS system AND the Russian GLONASS system together. Additionally, the receivers are also prepared to use Galileo and BeiDou signals as well. In detail, PAVE-IR, MCA 2000 Compaction Mapping System and 3D Earthmoving Systems are available with GNSS. Exact location, high precision and prevention of over- and under- compaction can be better achieved.

What are the different GNSS Systems?

1. The GPS (Global Positioning System) is the first GNSS system, which was launched in 1970 by the DOD (Department of Defense). Its first Initial Operational Capability (IOC) was in 1993. With a constellation of 24 to 32 satellites, it now provides global coverage. It was originally placed for military use only. Today, this service is free for civil users. In the year 2000 when SA (Selective Availability) was switched off, the accuracy increased from 100m to 20m. That was real push-through for civil usage.

Photo Credit: Novatel

2. GLONASS is the Russian system operated by the Russian government. The GLONASS Global constellation consist of 24 satellites. GLONASS operates on 3 planes with 64.8 degree from the equatorial plane, which is the highest gradient, and ensures best signal capturing close to the pole.

3. Galileo (Europe) This system is developed in close cooperation of the European Union and the ESA (European Space Agency). Thirty satellites are planned. The first two operational satellites were launched in October 2011. The full constellation will not be complete for several years.

4. BeiDou (China) BeiDou is the Chinese navigation satellite system. The system will consist of 35 satellites. The global service is planned for 2020 after its completion.

Why using GNSS?

The use of GLONASS and GPS together add up to a larger number of satellites, resulting in better coverage. In addition, the signal availability for the northern hemisphere is improved.

What are the main benefits are of using GLONASS and GPS together?
  • Reduced signal acquisition time
  • Improved position and time accuracy
  • Reduction of acquisition problems caused by buildings and planting (trees)
  • Improved spatial distribution of satellites in the field of view, which results in an improved precision
  • Can be used at any time of the day and under all weather conditions

What are the limitations of GNSS Positioning Systems?

There must be a clear view to at least four satellites. Sometimes the signals can be blocked by tall buildings, trees, etc. GNSS also can not be used indoors.

How does the basic structure of GNSS System look like?

Photo Credit: Novatel

  • GNSS satellites
  • Ground –based control stations
  • The satellites regularly broadcast
  • GNSS user equipment

How to determine the position?

All GPS positions are based on measuring the distance from the satellites to the receiver on the earth. If the distance to three points relative to one’s position is known, one can determine its own position relative to those three points.

By knowing the distance to one satellite, one can ensure that the position of the receiver must be at some point on the surface of an imaginary sphere, which has his origin at the satellite. By intersection of three imaginary spheres, the receiver position can be determined.

What is challenging is, that only pseudo ranges and the time when the signal arrives at the receiver, it can be determined. Thus, there are four unknowns to determine; position (XYZ) and time of travel of the signal. Observing four satellites provides four equations, which can be solved and enabling that these unknowns can be determined.

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Conclusion is that a GNSS systems is more accurate as more satellites can be seen and used to determine the position of a machine. The use of GLONASS and GPS together is the best state-of-the- art method to ensure accurate positioning. It will be interesting to see what impact Galileo and BeiDou will have when completed.

bmarx 04.12.2015 0 3344
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