llAngleBetween

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/LSL

AngleBetween

llAngleBetween

Summary

1 Bug

Function: float llAngleBetween( rotation a, rotation b );

174	Function ID
0.0	Forced Delay
10.0	Energy

Returns a float that is the angle in radians between rotation a and rotation b.

• rotation	a	–	start rotation
• rotation	b	–	end rotation

Caveats

Important Issues

~ All Issues ~ Search JIRA for related Bugs

SVC-2424

A

llAngleBetween() is sometimes inaccurate

Examples

<lsl> default {

   touch_start(integer num_detected)
   {
       rotation currentRootRotation = llGetRootRotation();
       float angle = llAngleBetween(ZERO_ROTATION, currentRootRotation);

       // PUBLIC_CHANNEL has the integer value 0
       llSay(PUBLIC_CHANNEL,
           "llAngleBetween(ZERO_ROTATION, " + (string)currentRootRotation + ") = " + (string)angle);
   }

}

</lsl>

See Also

Functions

•	llRotBetween
•	llRot2Angle	–	Similar functionality used for the Axis-Angle format

Deep Notes

Reference

<lsl>float AngleBetween(rotation a, rotation b)//simple but turns out to not be very accurate. {

   return 2.0 * llAcos( llFabs(a.x * b.x + a.y * b.y + a.z * b.z + a.s * b.s)
                     / llSqrt((a.x * a.x + a.y * a.y + a.z * a.z + a.s * a.s)
                            * (b.x * b.x + b.y * b.y + b.z * b.z + b.s * b.s)));

}</lsl>

<lsl>float AngleBetween(rotation a, rotation b)//more complex implementation but more accurate, and reasonably fast. {

   rotation r = b / a; // calculate the rotation between the two arguments as quaternion
   float s2 = r.s * r.s; // square of the s-element
   float v2 = r.x * r.x + r.y * r.y + r.z * r.z; // sum of the squares of the v-elements

   if (s2 < v2) // compare the s-component to the v-component
       return 2.0 * llAcos(llSqrt(s2 / (s2 + v2))); // use arccos if the v-component is dominant
   if (v2) // make sure the v-component is non-zero
       return 2.0 * llAsin(llSqrt(v2 / (s2 + v2))); // use arcsin if the s-component is dominant

   return 0.0; // one or both arguments are scaled too small to be meaningful, or the values are the same, so return zero

}//Written by Moon Metty & Miranda Umino. Minor optimizations by Strife Onizuka</lsl>

Watch for developments on this function with SVC-2424

All Issues

~ Search JIRA for related Issues

SVC-2424

A

llAngleBetween() is sometimes inaccurate

Signature
function float llAngleBetween( rotation a, rotation b );