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Course, in navigation, is the intended flight path of an airplane over the ground; or the direction of a line drawn on a chart representing the intended airplane path, expressed as the angle measured from a specific reference datum clockwise from 0° through 360° to the line. The reference can be true north or magnetic north and called true course or magnetic course respectively. Course is customarily expressed in three digits, using preliminary zeros if needed.

In order to be used in a chart, this reference has to be true north.

• Navigation (2) is the direction the vessel, aircraft or vehicle is truly "pointing towards" (the heading of the ship shown in the image is 058°).

• Any reading from a magnetic compass refers to compass north (4), which is supposed to contain a two-part compass error:
  a) The earth's magnetic field's north direction, or magnetic north (3), almost always differs from true north by magnetic variation (6), the local amount of which is given in nautical charts, and
  b) ship's own magnetic field may influence the compass by so-called magnetic deviation (5).
  Deviation only depends on the ship's own magnetic field and the heading, and therefore can be checked out and given as a deviation table or, graphically, as a Napier's diagram.

• The compass heading or compass course (7) has to be corrected first for deviation (the "nearer" error), wherefrom results the magnetic heading (8). Correcting this for variation yields true heading (2).

• In case of a cross wind (9), and/or tidal or other current (10), the heading will not meet the desired target, as the vessel will continuously drift sideways; it is necessary to point away from the intended course to counteract these effects.

Track

A track, also course over ground, is the actual path followed by a moving body, e.g. the vessel's track from A to B in the above given scheme. Some ambiguity exists in the fact that the path a navigator intends to follow, after evaluating and counteracting possible effects of wind and current, is also called track.

The track is equivalent to the heading (a bearing "right ahead"), if no cross wind and cross current occur (2), but this would hardly ever happen in aviation.

When wind is present, and is not a directly facing or tail wind, the wind deflects the aircraft (or vessel) from its heading.

To correct for the wind, the aircraft (or vessel) points more or less into the wind. The amount depends on the vehicle's speed, the wind's speed, and the angle of the wind in relation to the vehicle. This so-called wind correction angle is computed in advance and is frequently checked while "en route". In the above scheme, the track would be (9) for wind from port side.

GPX is an XML schema for storing track logs.

Notes:

• The above scheme shows a variation of 6° East, as might happen in areas of Pacific ocean, for instance, and
• a more-than-somewhat exaggerated deviation (taken from a fictitious deviation table for educational purpose) of +12°, for a compass heading of 040°. By conventional degaussing, deviation could usually be kept beyond 10°, and fluxgate compasses can be degaussed to almost D=0°.
• The possible influences of wind and current are maximized by presupposing a very slow boat in heavy wind and current.
• To increase readability of the scheme, all possible influences were given as positive, i.e. variation=East, + 12° deviation, wind and current from port side. The principle is the same for the opposite of any of the components.

See also

Template:Nautical portal

• Navigation

Reference

Pilot's Handbook of Aeronautical Knowledge http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/faa-h-8083-25-1of4.pdf

• Navigation