_ATAN2 - QB64Official/qb64 GitHub Wiki

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