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Second Life Creation

llAtan2

float llAtan2(float y, float x)

Returns the arc-tangent2 of y, x.

Parameters
y (float)
A floating-point value.
x (float)
A floating-point value.
Technical Details
  • Return Type: float
  • Energy: 10

Similar to arctangent(y/x) except it utilizes the signs of x and y to determine the quadrant and avoids division by zero.

Returns a value in the range [-PI, PI].

Specifications

Section titled “Specifications”

The function handles edge cases with zero values:

  • If x is positive zero:

    • If y is zero, zero is returned
    • If y is positive, PI/2 is returned
    • If y is negative, -PI/2 is returned

  • If x is negative zero:

    • If y is positive zero, PI is returned
    • If y is negative zero, -PI is returned
    • If y is positive, PI/2 is returned
    • If y is negative, -PI/2 is returned

Alternatively, this can be expressed as:

if((string)x != (string)0.0 && y == 0.0)  // negative zero
    return PI * ~-2*((string)y != (string)0.0));
return ((y > 0) - (y < 0)) * PI_BY_TWO;

Examples

Section titled “Examples”

Basic usage with random values:

default
{
  state_entry()
  {
    float num1 = llFrand(100.0);
    float num2 = llFrand(100.0);


    llOwnerSay("y = " + (string)num1);
    llOwnerSay("x = " + (string)num2);


    llOwnerSay("The arctangent of y divided by x is " + (string)llAtan2(num1, num2));
  }
}

Compass direction calculator (returns compass bearing based on target position):

// Function with input of a vector determining the position of a target and returning
// a string with the literal compass-direction of that target towards your position
// by Ramana Sweetwater 2009/01, any use allowed license :-)
// corrected by Patrick Muggins


string compass(vector target)
{
    vector source = llGetPos();
    list DIRS = ["W", "NW", "N", "NE", "E", "SE", "S", "SW", "W"];
    integer index = llCeil(3.5 - (4 * llAtan2(target.y - source.y, target.x - source.x) / PI));
    return llList2String(DIRS, index);
}

See Also

Section titled “See Also”