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Great Circle Calculator.

By Ed Williams

Once you get the hang of it, you'll find this calculator to be an invaluable tool. No longer will you need online degrees in mathematics to be able to compute true course and distance between two points. Just enter in the data, select your distance units and away you go! You'll find this calculator so handy that you may want to bookmark this site on your smartphone so you can access the information while you are out in the field.

Note * You need Javascript enabled if you want this page to do anything useful!

Compute true course and distance between points.

Enter lat/lon of points, select distance units and earth model and click "compute". Lat/lons may be entered in DD.DD, DD:MM.MM or DD:MM:SS.SS formats.

Lat1
Lon1
Input Data
Lat2
Lon2

Course 1-2
Course 2-1
Distance
Output

Distance Units: Earth model:


Compute lat/lon given radial and distance from a known point

Enter lat/lon of initial point, true course and distance. Select distance units and earth model and click "compute". Lat/lons may be entered in DD.DD, DD:MM.MM or DD:MM:SS.SS formats.

Lat1
Lon1
Course 1-2
Distance 1-2
Input data

Lat2
Lon2
Output

Distance Units: Earth model:


Spheroid

Enter "user defined" spheroid parameters here:

Major radius a (km): Inverse flattening 1/f:


History

7/13/98 Removed a line of debugging code, giving irritating Javascript alerts, left over from the 5/16/98 changes

5/16/98 Changed the great circle radial and distance algorithm to one valid for unlimited distances. Previous was only valid for ranges up to one quarter of the earth's circumference in longitude. Note that the Vicenty algorithm for (ellipsoidal) course and distance may fail to converge correctly, or at all, if the final point is within 37' of arc of the antipodes of the first point.

5/12/98 Eccentricity of NAD27 (Clarke1866) ellipsoid obtained from my reference "Coordinate Systems and Map Projections" by D. H. Maling was in error. 1/f changed from 298.97866982 to 294.9786982138

11/9/97 Fixed bug where if the output lat/lon was DD 6.MMMM (ie 6 minutes), the result was incorrectly rounded up to the next degree.

3/4/97 Fixed bug where deg/minute entries 08 or 09 would be (mis)read in octal!

Ed Williams
72347.1516@CompuServe.COM

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All contents ęCopyright 1996-2013 Ed Williams & FAR Labs. All Rights Reserved.