Sea chart

The sea chart is a particular type of chart which represents the elements essential to the sea Transport. In adequacy with the maritime indication, it makes it possible to be located and to move.

It indicates primarily the probe S and the Isobathe S (depth of water), the dangers (Récif S, shallow waters, stray S, immersed Munitions), the maritime regulation, the maritime Signalisation (Phare S, Balise S, Bouée S) and the Amer S.

The official sea charts are published by the official hydrographic services of the Coastal states; they engage the responsibility for the State in the event of error. Simplified or specialized versions intended for certain users (yachtmen) are also published in complement by private editors.

In complement or the traditional charts (paper), the hydrographic services publish from now on electronic charts, which can be visualized on systems (like ECDIS) directly interfaced with the instruments of navigation (GPS, Sondeur…)

History

The constitution of sea charts especially started as from the 15th century during the maritime expansion of the great European nations. They were especially the fact of the Portugal, of the Spain, the Netherlands.

The realization of these charts was also one of the essential missions of the Explorateur S of the time, Vasco de Gama, Ferdinand Magellan, Christophe Colomb, etc the states preserved these data like their more invaluable treasures.

It is at the 17th century, with the appearance of powerful measuring instruments, which the first precise charts of the coasts will appear. Most brilliant Cartographe S is then with the Netherlands, supported by the Compagnie Dutchwoman of the Eastern Indies. In France is created the body of the engineers cartographers.

The engineer Charles-François Beautemps-Bowsprit and his team carry out an exhaustive and precise cartography coasts of France between 1816 and 1844.

Standardization

Many States produce sea charts; convention SOLAS ( Safety Off Life At Sea , rule 9, chapter V) signed within the framework of the International Maritime Organization imposes besides on the States left with convention " to make provisions in order to gather and to compile the hydrographic data and to publish, diffuse and hold up to date all the nautical information necessary to ensure the safety of navigation . "

The official charts (traditional or electronic) generally respect the standards and recommendations of the international hydrographic Organization.

Projection, frame of reference

The sea charts use the Projection of Mercator name of its inventor Gerardus Mercator. It is a Projection in conformity which preserves the angles (what makes it possible to defer directly on the chart the angles measured the compass, and vice versa) but not the distances (the scale of the chart varying with the latitude).

They use several frames of reference:

an altimetric system to indicate the altitude of the terrestrial points useful for navigation;
a bathymetric system to indicate the depth of water compared to a reference;
a system of coordinated (geodetic System) to locate the elements related to the chart in Latitude and Longitude.

In France, the sea charts are published by SHOM. They use as references:

for altitude, the zero of the general levelling of France , frame of reference of IGN.
for the depth, the level zero of the sea charts , which corresponds to the water level of the low tide possible (see Marée S).
for the coordinates, WGS 84, geodetic System associated with the coordinates provided by GPS.

Attention the migration of the charts in WGS 84 is made only on the charts published since 2001. The majority of the old charts use for Europe the system European 1950 (ED50), or of the local systems; the corrections necessary to pass from these systems to the WGS 84 are generally about a few tens of meters, but can reach several hundred meters in certain areas of the world.

See too

External bonds

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