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

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);
    }
}

See Also

Functions

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

Deep Notes

Reference

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)));
}

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

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 );