TomNally_Atan2.bas

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tsh73 tsh73 Aug 30, 2010 

=Atan2.bas= 
companion program to the article
[[PolarPhun|UNDERSTANDING AND PLOTTING POLAR COORDINATES]] by //Tom Nally//

**Editor's note:**
This function works fine, just be aware that it returns angle in range 0..2Pi 
(and atan2 from C standard library returns angle in range -Pi..Pi)

[[code format="vbnet"]]
'***********************************************
'
'Atan2.bas by Nally + April 2000
'Released as open source
'
'A function called ATAN2() is provided herein.
'ATAN2() takes two arguements: cartesian x and y
'coordinates.  It returns an angle, phi, in'radians.
'
'ATAN2() differs from ATN() in this regard:
'while ATN() only returns an angle between
'-pi/2 and +pi/2, ATAN2() will return any
'angle in the full circle.
'
'The user should not call the function if both
'x and y = 0.  This corresponds to a point at
'the origin of the coordinate system where
'the angle phi has no meaning.
'
'***********************************************
     pi = 3.14159265
     Print " "
     Print "Note: Input real numbers for"
     Print " x and y. Either x or y"
     Print " or both must be non-zero."
     Print " "
     Print "** INPUT **"
     Print " "
Input "x = "; x
     Input "y = "; y
Print " "
     Print "** OUTPUT **"
     Print " "
phiRads = ATAN2(x, y)
     phiDegs = 360 * (phiRads / (2 * pi))
     R = (x^2 + y^2)^(1/2)
     Print "Cartesion Coordinates of Q....Q("; x; ", "; y;      ")"
     Print " "
     Print "ATAN2 in radians.............."; phiRads
     Print "ATAN2 in degrees.............."; phiDegs
     Print "Distance to Q................."; R
     Print " "
     Print "Polar Coordinates of Q........Q("; phiRads; ", ";      R;")"

     End
Function ATAN2(x, y)
     pi = 3.14159265
     Result$ = "Undetermined"
     If (x = 0) and (y > 0) Then
     ATAN2 = pi / 2
     Result$ = "Determined"
     End If
     If (x = 0) and (y < 0) Then
     ATAN2 = 3 * pi / 2
     Result$ = "Determined"
     End If
     If (x > 0) and (y = 0) Then
     ATAN2 = 0
     Result$ = "Determined"
     End If
     If (x < 0) and (y = 0) Then
     ATAN2 = pi
     Result$ = "Determined"
     End If
 If Result$ = "Determined" Then [End.of.function]
     BaseAngle = Atn(abs(y)/abs(x))
     If (x > 0) and (y > 0) Then ATAN2 = BaseAngle
     If (x < 0) and (y > 0) Then ATAN2 = pi - BaseAngle
     If (x < 0) and (y < 0) Then ATAN2 = pi + BaseAngle
     If (x > 0) and (y < 0) Then ATAN2 = 2*pi - BaseAngle
 [End.of.function]
End Function
[[code]]