QB64-website/wiki/_ATAN2.md

The _ATAN2 function returns the radian angle between the positive x-axis of a plane and the point given by the coordinates (x, y).

Syntax

angle! = _ATAN2(y, x)

Parameter(s)

• y is the vertical axis position (row) as a positive, zero or negative floating point value.
• x is the horizontal axis position (column) as a positive, zero or negative floating point value.

Description

• The DOUBLE radian angle returned is positive for upper row values where y > 0.
  • _ATAN2(y, x) = ATN(y# / x#) when x > 0
  • _ATAN2(y, x) = ATN(y# / x#) + _PI when x < 0
  • _ATAN2(y, x) = _PI / 2 when x = 0
• The DOUBLE radian angle returned is 0 when x > 0 and _PI when x < 0 where y = 0
• The DOUBLE radian angle returned is negative for lower row values where y < 0.
  • _ATAN2(y, x) = ATN(y# / x#) when x > 0
  • _ATAN2(y, x) = ATN(y# / x#) - _PI when x < 0
  • _ATAN2(y, x) = -_PI / 2 when x = 0
• _ATAN2(0, 0) is undefined and the function returns 0 instead of a division error.

Error(s)

• With ATN(y / x), x can never be 0 as that would create a Division by Zero ERROR Codes 11 or #IND.

See Also

• ATN (arctangent)
• _PI (QB64 function)
• Mathematical Operations
• Atan2 reference