SimpleCamera simpleCamera(const Matrix& P) {
// P = [A|a] = s K cRw [I|-T], with s the unknown scale
Matrix A = P.topLeftCorner(3, 3);
Vector a = P.col(3);
// do RQ decomposition to get s*K and cRw angles
Matrix sK;
Vector xyz;
boost::tie(sK, xyz) = RQ(A);
// Recover scale factor s and K
double s = sK(2, 2);
Matrix K = sK / s;
// Recover cRw itself, and its inverse
Rot3 cRw = Rot3::RzRyRx(xyz);
Rot3 wRc = cRw.inverse();
// Now, recover T from a = - s K cRw T = - A T
Vector T = -(A.inverse() * a);
return SimpleCamera(Pose3(wRc, T),
Cal3_S2(K(0, 0), K(1, 1), K(0, 1), K(0, 2), K(1, 2)));
}
