OpenSim.Region.ScriptEngine.Shared.Api.LSL_Api.llRotBetween C# (CSharp) Method

        public LSL_Rotation llRotBetween(LSL_Vector a, LSL_Vector b)
        {
            //A and B should both be normalized
            m_host.AddScriptLPS(1);
            /*  This method is more accurate than the SL one, and thus causes problems
                for scripts that deal with the SL inaccuracy around 180-degrees -.- .._.
                
            double dotProduct = LSL_Vector.Dot(a, b);
            LSL_Vector crossProduct = LSL_Vector.Cross(a, b);
            double magProduct = LSL_Vector.Mag(a) * LSL_Vector.Mag(b);
            double angle = Math.Acos(dotProduct / magProduct);
            LSL_Vector axis = LSL_Vector.Norm(crossProduct);
            double s = Math.Sin(angle / 2);

            double x = axis.x * s;
            double y = axis.y * s;
            double z = axis.z * s;
            double w = Math.Cos(angle / 2);

            if (Double.IsNaN(x) || Double.IsNaN(y) || Double.IsNaN(z) || Double.IsNaN(w))
                return new LSL_Rotation(0.0f, 0.0f, 0.0f, 1.0f);

            return new LSL_Rotation((float)x, (float)y, (float)z, (float)w);
            */
            
            // This method mimics the 180 errors found in SL
            // See www.euclideanspace.com... angleBetween
            LSL_Vector vec_a = a;
            LSL_Vector vec_b = b;
            
            // Eliminate zero length
            LSL_Float vec_a_mag = LSL_Vector.Mag(vec_a);
            LSL_Float vec_b_mag = LSL_Vector.Mag(vec_b);
            if (vec_a_mag < 0.00001 ||
                vec_b_mag < 0.00001)
            {
                return new LSL_Rotation(0.0f, 0.0f, 0.0f, 1.0f);
            }
            
            // Normalize
            vec_a = llVecNorm(vec_a);
            vec_b = llVecNorm(vec_b);

            // Calculate axis and rotation angle
            LSL_Vector axis = vec_a % vec_b;
            LSL_Float cos_theta  = vec_a * vec_b;
    
            // Check if parallel
            if (cos_theta > 0.99999)
            {
                return new LSL_Rotation(0.0f, 0.0f, 0.0f, 1.0f);
            }
            
            // Check if anti-parallel
            else if (cos_theta < -0.99999)
            {
                LSL_Vector orthog_axis = new LSL_Vector(1.0, 0.0, 0.0) - (vec_a.x / (vec_a * vec_a) * vec_a);
                if (LSL_Vector.Mag(orthog_axis)  < 0.000001)  orthog_axis = new LSL_Vector(0.0, 0.0, 1.0);
                return new LSL_Rotation((float)orthog_axis.x, (float)orthog_axis.y, (float)orthog_axis.z, 0.0);
            }
            else // other rotation
            {
                LSL_Float theta = (LSL_Float)Math.Acos(cos_theta) * 0.5f;
                axis = llVecNorm(axis);
                double x, y, z, s, t;
                s = Math.Cos(theta);
                t = Math.Sin(theta);
                x = axis.x * t;
                y = axis.y * t;
                z = axis.z * t;
                return new LSL_Rotation(x,y,z,s);
            }
        }