llAtan2

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/LSL

Atan2

llAtan2

Summary

Function: float llAtan2( float y, float x );

0.0	Forced Delay
10.0	Energy

Returns a float that is the  arctangent2 of y, x.

• float	y
• float	x

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

Specification

[9:10] Object: llAtan2(+0, +0) = 0.000000 [9:10] Object: llAtan2(+0, -0) = 3.141593 [9:10] Object: llAtan2(-0, +0) = 0.000000 [9:10] Object: llAtan2(-0, -0) = -3.141593

If x is positive zero and...

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

If x is negative zero and...

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

Or <lsl> 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; </lsl>

The returned value is in the range [-PI, PI]^[1].

Examples

<lsl>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));
 }

}</lsl><lsl>//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);

}</lsl>

/Compass QA

See Also

Functions

• llSin	llAsin	–	sine & inverse Sine
• llCos	llAcos	–	cosine & inverse cosine
• llTan		–	tangent

Articles

•	Atan2
•	Inverse trigonometric function

Deep Notes

Footnotes

1. ^ The ranges in this article are written in Interval Notation.

Signature
function float llAtan2( float y, float x );