code: def coords_for_observations(self):
          
          if self._compute_at_vertices:
              return self.vertices - self._pos_center
          else:
              return self.centers - self._pos_center
docs: Return the coordinates from the center of the star for each element
          (either centers or vertices depending on the setting in the mesh)
          after perturbations (either by features or by offsetting to get
          the correct volume).  NOTE: this is NOT necessarily where the physical
          parameters were computed, but IS where eclipse detection, etc, is
          handled.