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