The navigation with the regard is a method of Navigation which consists in deducing the position from a vehicle (terrestrial, maritime, air or space; controlled or automatic) of its road and the distance covered since its last known position. Traditionally, this method rests on the instruments measuring its Cape (compass), its speed (log, tachometer, Badin…) and time (stop watch) like with the possible estimate (or the calculation) of the influence of the environment (running, wind) on its walk.

It is dubious, because dependant on the measuring accuracy of the true road (or road on the bottom for a ship) and its real speed. In practice, in sea transport, one adopts an uncertainty equal to 2 to 3% of the distance covered, but which can reach 5% if the weather conditions are bad. With a control of the position at least once per day, one can admit permanently a ray of uncertainty always lower than 15 marine miles.

Calculation of the estimated point

$M\; \backslash ,$ being the distance covered with the road $R\_v\; \backslash ,$; $\backslash \; varphi\_a,\; G\_a\; \backslash ,$ and $\backslash \; varphi\_b,\; G\_b\; \backslash ,$ geographical coordinates of the starting points and arrival:

$\backslash \; varphi\_b\; =\; \backslash \; varphi\_a\; +\; M\; \backslash \; cos\; R\_v\; \backslash ,$

and $G\_b\; =\; G\_a\; +\; \backslash \; frac\; \{M\; \backslash \; sin\; R\_v\}\; \{\backslash \; cos\; \backslash \; varphi\_m\}\; \backslash ,$

with $\backslash \; varphi\_m\; =\; \backslash \; frac\; \{\backslash \; varphi\_a\; +\; \backslash \; varphi\_b\}\; \{2\}\; \backslash ,$

This approximate formula remains precise near with 1 nautical for nautical.

The calculators of regard directly give the courses in minutes of latitude (indicator NS) and longitude (indicator EW). Simple algebraic additions thus allow the calculation of the point.

Formerly, these calculations, hard, were carried out by means of “table of points” (in France, table 900 or counts of Friocourt,). They in addition required to note with rigor in the newspaper of navigation the changes of road and speed. The current was treated like an additional course.

At the time of the navy with veil, the men of quarter used a Renard (marine), memory assistance makes of a generally bored board of holes (the sailors were for the majority illiterate) and where they put cards to note the roads and speeds, various observations, which were used then for the navigator to calculate his regard.

Today, with the satellite appearance of the navigation systems, this method lost of its interest. It is however about an autonomous means. This is why it is recommended to preserve the data making it possible to hold a regard even when one has other means of positioning.

Inertial navigation

The use of an Inertial unit (which measures accelerations on the 3 axes) makes it possible to be freed from uncertainties due to the environment. The best power stations allow a precise navigation less one thousand sailor, without retiming of the position during several days.

But it is about an expensive system, which is practically used only in the military field, particularly on board submarines. It is also used on board automatic machines like the cruise missiles: their relatively short duration of flight allows the use of inertial units less sophisticated than on board submarines.

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