Great-circle navigation

Great-circle navigation

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.

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.

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.

See also

* Great circle
* Great circle distance
* Rhumb line

Resources

* [http://mathworld.wolfram.com/GreatCircle.html Great Circle – from MathWorld] Great Circle description, figures, and equations. Mathworld, Wolfram Research, Inc. c1999
* [http://gc.kls2.com/ Great Circle Mapper] Interactive tool for plotting great circle routes.
* [http://williams.best.vwh.net/gccalc.htm Great Circle Calculator] deriving (initial) course and distance between two points.
* [http://www.acscdg.com/ Great Circle Distance] Graphical tool for drawing great circles over maps. Also shows distance and azimuth in a table.


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