atan2 ( y ; x )

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

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Michael George - Show more from this author Michael George Consulting

  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, Ca Dec 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 Consulting Sep 28, 2013
Excel has the two parameters reversed: http://en.wikipedia.org/wiki/Atan2#Variations

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