 # atan2 ( y ; x )

returns the base angle (arctan) of a triangle with the sides X and Y.     Average rating: 3.9 (41 votes) Log in to vote Michael George - Show more from this author Michael George Consulting
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...

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

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.

## Comments Rouel Fernandez, Mountain View, CaDec 22, 2010 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) Michael George, Michael George ConsultingSep 28, 2013 Excel has the two parameters reversed: http://en.wikipedia.org/wiki/Atan2#Variations

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

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