osg,由eye,center,up生成的左乘，右手坐标系的矩阵

    Vec3d f(center-eye);
    f.normalize();
    Vec3d s(f^up);
    s.normalize();
    Vec3d u(s^f);
    u.normalize();

    set(
        s[0],     u[0],     -f[0],     0.0,
        s[1],     u[1],     -f[1],     0.0,
        s[2],     u[2],     -f[2],     0.0,
        0.0,     0.0,     0.0,      1.0);//旋转分量

    preMultTranslate(-eye);//平移分量

    //------可以从线性相关表示

     E(x, y,z) = E(eye1, eye2, eye3) + (s, u, -f)(x1, y1, z1);

     (x1, y1, z1)= (x - eye1, y - eye2, z - eye3) * (s, u, -f);

     x1, y1,z1为某点在(s, u,-f)组成的右手观察坐标系下的坐标，x,y,z为某点在单位E下的坐标

    受眼睛的位置影响，在第四行 osg::vec3d v = -eye;

   mm[4][0] = v[0] * s[0] + v[1] * s[1] + v[2] * s[3];

   mm[4][1] = v[0] * u[0] + v[1] * u[1] + v[2] * u[3];

   mm[4][2] = v[0] * f[0] + v[1] * f[1] + v[2] * f[3];

void Matrix_implementation::getLookAt(Vec3f& eye,Vec3f& center,Vec3f& up,value_type lookDistance) const
{
    Matrix_implementation inv;
    inv.invert(*this);

    eye = osg::Vec3f(0.0,0.0,0.0)*inv;

    up = transform3x3(*this,osg::Vec3f(0.0,1.0,0.0));

    center = transform3x3(*this,osg::Vec3f(0.0,0.0,-1));

    center.normalize();

    center = eye + center*lookDistance;
}