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GWP - TOPOGRAPHY
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TOP EYE The Top Eye system by SAAB Combitech uses a scanner laser and a differential GPS to make a topographic raising with notable low costs and centimetric accuracy. A helicopter with a flying automated system is used where the position is statistically treated at the rate of 7000 readings per second. This a friendly with the environment system, it does not need to build roads and it has the capacity to distinguish an object with a diameter of 10 cm. |
Top Eye: Ecologic aerial topography of latest generation |
GPS TOPOGRAPHY
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Satellites transmit signals generated by atomic oscilators (Cs or Rb) sent to the GPS receivers. Thanks to this the sphere radius that has the satellite as its centre and the receiver on the surface can be determined. As data, the travelling time and the light speed must be gotten. In order to determine the 3D position of the receiver three spheres are needed (three equations and three unknown quantities) an a fourth sphere to determine the error of the receiver stopwatch. It's important to say that the system was designed in a way that from everywhere and at anytime could be always observed a minimum of four satellites. Band L modulate three codes: |
 GPS (blue) and GLONASS (red) In the figure are displayed the GPS american system (blue) and the GLONASS russian system (red) These two systems, joined to the european ENSS system, allow to increase the cover in the "urban gorges" (building, hills, etc.) The latest famous application of this kind of navigation was done during the Persian Gulf War, where the Multinational Forces were oriented in the Iraqi desert with the GPS (they obviously didn't have an error of 18 meters...) |
The SPS and PPS codes allow to calculate the distance between the satellite and the receiver. L1 is modulated with SPS and PPS, while L2 is modulated just with PPS with the objective that unauthorized users measure a wrong time of travel, what leads to an error of 18 meters to the common man.
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The Global Position System (GPS) receives information from NAVSTAR satellites, which have the following characteristics:
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