In this paper we present a novel method to obtain the ground plane orientation. We assume that multiple objects are moving rigidly on a ground plane observed by a fixed camera. With an automatic tracking of some object features we do a classical “Structure from Motion” (SfM) method. This give us a static object viewed for a hypothetical camera called a “virtual camera”. This camera shares the same intrinsic parameters with the real camera but moves differently due to real object motion. Assuming that the object rotates around the plane normal (equivalent to say over the ground plane), and that the virtual camera will rotate around the same vector, we use the virtual camera positions along the sequence to estimate this rotation axis, the ground plane normal.