GreatCirc 1.0

GreatCirc is a software that lets you calculate great circle distances on the earths surface, and also plotting points or great circle paths from a world map.

The "great circle path" is the shortest direct route between two points on the earths surface. Because the earth is a globe, the shortest path between any two points lies on a circle which is centred at the earths 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 beause of the distortion inherent in mapping the globe onto a flat map. See the Wikipedia article for further information on great circle distance.

GreatCirc will calculate both the common "Direct Problem" and the "Inverse Problem", as well as doing a separate "Coverage Area" calculation. For the Direct Problem, given a starting point and the initial bearing and distance it will calculate the latitude and longitude at the destination.

For the Inverse problem, it will calculate the distance and azimuth bearings between any two points, given the latitude and longitude. In both cases, GreatCirc will plot the resulting Great Circle path on a world map.

GreatCirc will also do a coverage area calculation, given a centre point and a range, it will plot the resulting circle on a world map and calculate the area of the earths surface enclosed within the circle.

Great Circle calculations are based on spherical geometry, and can be relatively simple if the earth is assumed to be a perfect sphere. However, the earth is known to be in fact a flattened ellipsoid and not a sphere at all.

GreatCirc uses the standard WGS84 ellipsoid earth model commonly found on GPS receivers, to provide the most accurate calculations, however the option to do calculations using a spherical earth model is also available to allow comparisons between the two techniques. To perform the WGS84 ellipsoid calculations, GreatCirc uses the Vincenty algorithm.

A batch mode is also available to allow calculation of multiple distances and waypoints along a path and plot them on the world map.

GreatCirc may be of interest to mapping professionals interested in finding true distances between locations on the earths surface, or the general public interested in plotting their travels on a world map

NOTE:

The basic calculator function can be downloaded and used free of charge. To access the extended batch mode, file exporting, and magnetic azimuth tools you will need to register.