/// <summary>
/// Convert this instance to an axis-angle representation.
/// </summary>
/// <returns>A Vector4 that is the axis-angle representation of this quaternion.</returns>
public static Vector4 ToAxisAngle(this Quaternion q)
{
if (q.W > 1.0f)
{
q = Quaternion.Normalize(q);
}
float w = 2.0f * (float)System.Math.Acos(q.W); // angle
float den = (float)System.Math.Sqrt(1.0 - q.W * q.W);
if (den > 0.0001f)
{
return(new Vector4(new Vector3(q.X, q.Y, q.Z) / den, w));
}
else
{
// This occurs when the angle is zero.
// Not a problem: just set an arbitrary normalized axis.
return(new Vector4(Vector3.UnitX, w));
}
}
