In the case of liver tumor resections, Minimally Invasive Surgery (MIS) poses several benefits over open surgery. However, MIS makes navigating the surgical scene considerably more challenging, which hampers the realization of its full potential. Many Image Guidance Navigation Systems (IGS) have been proposed to overcome these challenges. The majority of these depend on optical tracking systems, whose additional setup overhead is a barrier to clinical translation. In this paper we put forward an IGS prototype which eliminates the need for optical tracking, and additionally incorporates a user-oriented camera calibration method which is more reliable and faster than typical checkerboard methods. We lastly make publicly available the core system modules for 3D reconstruction and rigid registration.