Greetings.
The camera model can offset cameras’ centres, thus to obtain correct camera centre, get it from ISfmCameraModel->GetCameraCentre().
In computer graphics are commonly used homogeneous coordinates to allow affine transformations. Simply said, a four-vector is used to represent 3d position with the fourth element carrying additional information.
In this case You shall normalize the point by dividing all its elements by the fourth element (thus the fourth element would become 1.0), but ISfmCameraModel->GetCameraCentre() shall already return normalized vector. So You can directly use the position and ignore the fourth element (, or to be sure assert in code that it equals to one).