Algorithms

public static float[] ToEuler(double tmp_x, double tmp_y, double tmp_z,double tmp_w)
{
    float[] Euler = new float[3];
    double sqr_X = tmp_x * tmp_x;
    double sqr_Y = tmp_y * tmp_y;
    double sqr_Z = tmp_z * tmp_z;
    double sqr_W = tmp_w * tmp_w;

    const double radian = 180 / Math.PI;
    double check = tmp_x * tmp_y + tmp_z * tmp_w;
    double unit = sqr_X + sqr_Y + sqr_Z + sqr_W;
    if (check > 0.499 * unit)
    {
        Euler[0] = 0;
        Euler[1] = (float)(radian * Math.Atan2(tmp_x, tmp_w));
        Euler[2] = (float)90;
        return Euler;
    }
    else if (check < -0.499 * unit)
    {
        Euler[0] = 0;
        Euler[1] = (float)(-radian * Math.Atan2(tmp_x, tmp_w));
        Euler[2] = (float)-90;
        return Euler;
    }

    Euler[0] = (float)(radian * (Math.Atan2(2 * (tmp_x * tmp_w + tmp_y * tmp_z), (-sqr_X - sqr_Y + sqr_Z + sqr_W))));
    Euler[1] = (float)(radian * (Math.Asin(-2 * (tmp_x * tmp_z - tmp_y * tmp_w))));
    Euler[2] = (float)(radian * (Math.Atan2(2.0 * (tmp_x * tmp_y + tmp_z * tmp_w), (sqr_X - sqr_Y - sqr_Z + sqr_W))));
    return Euler;
}

public static float[] ToEulerA(double x, double y, double z, double w)
{
    //double w = Convert.ToDouble(br.ReadSingle());
    //double x = Convert.ToDouble(br.ReadSingle());
    //double y = Convert.ToDouble(br.ReadSingle());
    //double z = Convert.ToDouble(br.ReadSingle());
    double sqw = w * w;
    double sqx = x * x;
    double sqy = y * y;
    double sqz = z * z;
    double unit = sqx + sqy + sqz + sqw;
    double test = x * y + z * w;
    double RX = 0;
    double RY = 0;
    double RZ = 0;

    if (test > 0.499 * unit)
    {
        RX = 2 * Math.Atan2(x, w);
        RY = Math.PI / 2;
        RZ = 0;
    }
    else if (test < -0.499 * unit)
    {
        RX = -2 * Math.Atan2(x, w);
        RY = -Math.PI / 2;
        RZ = 0;
    }
    else
    {
    RX = Math.Atan2(2 * y * w - 2 * x * z, sqx - sqy - sqz + sqw);
    RY = Math.Asin(2 * test / unit);
    RZ = Math.Atan2(2 * x * w - 2 * y * z, -sqx + sqy - sqz + sqw);
    }
    RX = 180 / Math.PI * RX;
    RY = 180 / Math.PI * RY;
    RZ = 180 / Math.PI * RZ;
    return new float[] { (float)RX, (float)RY, (float)RZ };
}