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Gunamoi Software
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GreatCirc Program 
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GreatCirc is a tool for calculating Great Circle distances on the earth's surface, and plotting points and great circle paths on a world map. (click here to see some screen shots) Anyone may download and install GreatCirc 2.0 to access the basic features free of charge.
The "great circle path" is the shortest direct route between two points on the earth's surface. Because the earth is a globe, the shortest path between any two points lies on a circle which is centred at the earth's core and passes around the surface of the world. Such a path will appear to be a curved line when drawn on a flat world map because of the distortion inherent in mapping the globe onto a flat map. See the Wikipedia article for further information on great circle distance. GreatCirc can calculate the Great Circle Distance between any two points on the earth. Also, given a starting point, direction and distance it can calculate the Great Circle End Point. In both cases, GreatCirc will plot the resulting Great Circle path on a world map. GreatCirc can also do a Coverage Area calculation, given a centre point and a range, GreatCirc will plot the resulting circle on a world map and calculate the area of the earth's surface enclosed within the circle. New, in version 2.0, GreatCirc can also calculate and plot the Rhumb Line distance between two locations. In navigation, a rhumb line (or loxodrome) is a line crossing all meridians of longitude at the same angle, i.e. a path derived from a defined initial bearing. That is, upon taking an initial bearing, one proceeds along the same bearing, without changing the direction as measured relative to true north. See the Wikipedia article The following maps, produced using GreatCirc, show the Great Circle shortest distance line between London and Beijing in white. They also show the Rhumb Line of constant bearing in green. The Rhumb line appears shorter on a flat map, and may be easier to navigate on a constant bearing, but in fact is significantly longer. London - Beijing: Great Circle Distance (white line) = 8,180km, Rhumb Line distance (green line) = 9,142km. The following is an equidistant rectangular map projection produced using the Basic (free) version of GreatCirc 2.0.
The following is a global view produced using the Advanced (registered) version of GreatCirc 2.0.
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