 # 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:
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. 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