Great-circle navigation

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Great-circle navigation is the practice of navigating a vessel (such as a ship or aircraft) along a track that follows a great circle. A great circle track is the shortest distance between two points on the surface of the earth.

Contents 1 Methods 1.1 Gnomonic chart 1.2 Spherical trigonometry 1.3 Computer software 2 See also 3 Resources

[edit] Methods

In order to construct a great circle track, the navigator of a ship may employ several methods.

[edit] Gnomonic chart

A straight line drawn on this chart would represent a great circle track. When this is transferred to a Mercator chart, it becomes a curve. The positions are transferred at a convenient interval of longitude and this is plotted on the Mercator chart with the appropriate latitude.

[edit] Spherical trigonometry

Mathematically, it is possible to determine the distance of a great circle track between two known positions. Other features of the great circle track may also be calculated.

[edit] Computer software

Software is available that allows a navigator to input a departure and arrival position to create a list of waypoints which follow a great circle track. Normally, such programs will also calculate the total distance, the distance between successive waypoints, and the courses to be followed between successive waypoints.

[edit] See also

• Great circle
• Great circle distance
• Rhumb line

[edit] Resources

• Great Circle – from MathWorld Great Circle description, figures, and equations. Mathworld, Wolfram Research, Inc. c1999
• Great Circle Mapper Interactive tool for plotting great circle routes.
• Great Circle Calculator deriving (initial) course and distance between two points.
• Great Circle Distance Graphical tool for drawing great circles over maps. Also shows distance and azimuth in a table.