1. A computer assisted, non-radiological method of intra-operatively measuring and assessing relative geometric relationships among skeletal features of a hip joint, suitable for surgical navigation of a hip arthroplasty operation, comprising the steps of: defining a pelvic plane from at least three recognizable anatomic features of the pelvis; tracking with a locating system the orientation of an acetabular implant, to obtain acetabular implant orientation data; and adjusting said acetabular implant into a desired orientation with respect to said defined pelvic plane, without reference to previously obtained radiological data, by relating said acetabular implant orientation data to said defined pelvic plane.