Tags each `Monomer` in the `Assembly` with its helical geometry.

        Parameters
        ----------
        force : bool, optional
            If True the tag will be run even if `Monomers` are already tagged.
        reference_axis : list(numpy.array or tuple or list), optional
            Coordinates to feed to geometry functions that depend on
            having a reference axis.
        reference_axis_name : str, optional
            Used to name the keys in tags at `Chain` and `Residue` level.

def tag_ca_geometry(self, force=False, reference_axis=None,
                        reference_axis_name='ref_axis'):
        """Tags each `Monomer` in the `Assembly` with its helical geometry.

        Parameters
        ----------
        force : bool, optional
            If True the tag will be run even if `Monomers` are already tagged.
        reference_axis : list(numpy.array or tuple or list), optional
            Coordinates to feed to geometry functions that depend on
            having a reference axis.
        reference_axis_name : str, optional
            Used to name the keys in tags at `Chain` and `Residue` level.
        """
        for polymer in self._molecules:
            if polymer.molecule_type == 'protein':
                polymer.tag_ca_geometry(
                    force=force, reference_axis=reference_axis,
                    reference_axis_name=reference_axis_name)
        return