We present a method for estimating the viewpoint from which a 3D image has been taken using a central-projection range sensor. We assume we have the 3D coordinates of the points, organized with a known topology, but considerable noise is present in the data. At points in the scene where there are surface discontinuities, we estimate step rays through a linear interpolation. The viewpoint is found as the point of minimum distance to the set of step rays. To cope with noise, we define an unbiased distance measure. The minimization of the sum of distances provides the viewpoint. We present results of several experiments carried out with 3D images of an old church.