fnLatLon.bearing ( lat1 ; lon1 ; lat2 ; lon2 )

Calculates initial bearing between two points on Earth's surface.

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Michael George - Show more from this author
Michael George Consulting

Sample input:

fnLatLon.bearing ( 45.0638888 ; -64.1808333 ; 44.6205555 ; -65.7583333 )

Sample output:

248.936

Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

//  Modified from: Ed Williams' Aviation Formulary, http://williams.best.vwh.net/avform.htm#Crs
//  Calculates (initial) bearing between two points on Earth's surface.
//  input:
//  lat1, long1, lat2, long2 = lat and long of 2 points, in degrees Decimal.
//  output: initial bearing between the 2 points in degrees Decimal.
Let(
    [
        lat1R = Radians( lat1 );
        lat2R = Radians( lat2 );
        dLon = Radians( lon2 ) - Radians( lon1 );
        y = Sin( dLon ) * Cos( lat2R );
        x = Cos( lat1R ) * Sin( lat2R ) - Sin( lat1R ) * Cos( lat2R ) * Cos( dLon );
        theResult = Degrees( fnAtan2( y; x ) )
    ];
    theResult
)

This calculates the initial bearing for following a great-circle arc from a starting Latitude & Longitude to a destination Latitude & Longitude.

Please note that this function requires the Atan2 function that I have also listed on this site.

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Note: these functions are not guaranteed or supported by BrianDunning.com. Please contact the individual developer with any questions or problems.

fnLatLon.bearing ( lat1 ; lon1 ; lat2 ; lon2 )

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