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# FileMaker Pro Custom Functions

atan2 ( y ; x )

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Discuss this Custom Function

Michael George, Michael George Consulting
mailto:mgeorge@coresupport.com

returns the base angle (arctan) of a triangle with the sides X and Y.

Sample Input:
 atan2 ( y ; x ) 1 0 1 1 0 1 -1 1 -1 0 -1 -1 0 -1 1 -1
Sample Output:
 (in radians) 0 0.7853... 1.5707... 2.3561... 3.1415... 3.9269... 4.7123... 5.4977...

Then copy & paste into FileMaker Advanced's Edit Custom Function window.

## Description:

The function atan2(y;x) returns the arctan of y,x with adjustments for the signs of x and y so that the angle returned is the angle of the cartesian point (x,y) in radians.
The commonest use of atan2 is in converting between rectangular and polar co-ordinates. The formula for calculating the *initial* heading for a great-circle route from point A to point B uses atan2.
Please be aware that the parameter order is y,x and not x,y as usual.

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

This is my Custom Function and I want to edit it

## Discuss:

The above does not give the same results as Microsoft Excel. I use the following, Note the special for x=0 and y=0, I define ATAN2(x,y) = 0:

Let ( [
a =
Case ( x > 0 ; Atan( y / x ) ;
x < 0 ; If ( y ≥ 0 ; Pi + Atan ( y / x) ; -Pi + Atan ( y / x)) ;
x = 0 ; If ( y > 0 ; Pi / 2 ; If ( y < 0 ; -Pi / 2 ; 0) )) ;
result =a
];
result
)

Convert from 0 to 2*pi: result = mod ( 2* pi + a ; 2 * pi)

Rouel Fernandez, Mountain View, Ca
December 22, 2010 7:20am

Excel has the two parameters reversed:
http://en.wikipedia.org/wiki/Atan2#Variations

Michael George, Falmouth,NS
September 28, 2013 9:25pm