The navigation is the science and the whole of the techniques which allow:

• to know the position (its coordinates) of a mobile compared to a frame of reference, or a point fixes given;
• to calculate or measure the road to be followed to join another point of known coordinates;
• to calculate any other relative information with the displacement of this mobile (distances and durations, rate of travel, estimated hour of arrival, etc).

## Aerial navigation and sea transport

The principles of the aerial navigation are identical to those of sea transport. The first instruments used aboard aircraft are directly from the instruments used in the navy. The systems of Radionavigation also used in sea Transport, particularly diversified and developed with the profit of the Aerial navigation, in particular for the approaches of aerodromes and guidance with the landing. Since their appearance in the years 1970, navigation uses satellite systems. The receivers used in aeronautics are identical to those used on the ground or at sea.

In aeronautics:

• the function piloting , i.e. the control of the flight of the plane compared to the air is exerted thanks to the instruments. One can associate with it the instruments which control the parameters of the engines.
• the function radiocommunication allows the information exchange between an aircraft and the controlling authorities of navigation on the ground.
• the instruments corresponding to these three functions are gathered on the instrument panel which constitutes the IHM, interfaces man-machine, between the pilot and the aircraft.

## Reference and problems

On the Earth, navigation requires a frame of reference, known as geodetic Système. The system from now on more used is the WGS84 ( World Geodetic System, 1984 ), but of many charts still use an older geodetic system.

Knowing the coordinates of the mobile and those of the place of destination, one can then calculate (or measure on a chart) the route to follow to join this last point, which can be in particular:

• a road with constant course (with constant angle with the meridian lines), the Loxodromic curve;
• or the shortest road, the Orthodromie, i.e. a Géodésique (an arc of Grand circle, if one compares the ground to a sphere);
• or another more complex road, according to the external conditions (meteorology, currents, wind…) or of the selected constraints (maximum speed, minimal consumption, etc).

## Historical evolution

The techniques of navigation were developed by the first sailors to sail on the seas and oceans. The observation of the terrestrial magnetism very early led to the invention of the Boussole (called in navigation a compass), which made it possible to hold a course and to follow a road. The velocity measurement was made possible thanks to the invention of the log to boat. These two elements, course and speed, allow a Navigation the regard, insufficiently precise in the duration. Without terrestrial reference mark (out of sight of a coast), the navigators located themselves thanks to the observation of the stars. The height of a star to the top of the horizon, easily measurable by the “ancestors” of the Sextant, such as the Astrolabe, makes it possible to calculate the latitude. All these techniques were acquired, as of XVe century. The measurement of longitude, which results from the measurement of time, was truly possible only at the XVIIIe century with the invention of stop watch (or chronometer) precise which made it possible “to keep” the time of the prime meridian.

Thereafter, these means gained in precision and the methods of calculating were refined. At the end of XIXe, the invention of electricity involved that of the gyroscopic compass which makes it possible to be freed from the difficulties inherent in the terrestrial magnetism. The development of radio allowed in first half of the XXe century, the arrival of the first systems of Radionavigation (principle of the Radiogoniométrie in the beginning). Those diversified and developed, particularly with the profit of the Aerial navigation, in particular for the approaches of aerodromes and guidance with the landing.

Starting from the end of the XXe century appeared the satellite systems of navigation. The basic principle is identical to the radionavigation, but the beacons are established on a satellite constellation of S in orbit. The low costs of the receivers make it possible to consider the equipment of the most rustic mobiles. The satellite systems, in sea transport, supplanted all the existing systems of radionavigation.

The old techniques containing Sextant S and of Chronomètre S, which does not use electrical energy, remain always relevant because they constitute a means of help in the event of failure (accidental or voluntary) of the systems of positioning, even the only means on traditional sailing ships of pleasure.

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