docs: def projection(self, **kwargs):
          """
          The elliptical cut of an ellipsoidal
          conic describing all points of tangency
          to the conic as viewed from the origin.
          """
          viewpoint = kwargs.pop('viewpoint', None)
          if viewpoint is None:
              ndim = self.shape[0]-1
              viewpoint = N.zeros(ndim)
          plane = self.polar_plane(viewpoint)
          return self.slice(plane, **kwargs)