def geom(self):
        """Geometry information.

        :class:`_Geometry` instance holding geometry information. It is
        issued from binary files holding field information. It is set to
        None if not available for this time step.
        """
        if self._header is UNDETERMINED:
            binfiles = self.step.sdat.binfiles_set(self.step.isnap)
            if binfiles:
                self._header = stagyyparsers.fields(binfiles.pop(),
                                                    only_header=True)
            elif self.step.sdat.hdf5:
                xmf = self.step.sdat.hdf5 / 'Data.xmf'
                self._header, _ = stagyyparsers.read_geom_h5(xmf,
                                                             self.step.isnap)
            else:
                self._header = None
        if self._geom is UNDETERMINED:
            if self._header is None:
                self._geom = None
            else:
                self._geom = _Geometry(self._header, self.step.sdat.par)
        return self._geom
Geometry information.

        :class:`_Geometry` instance holding geometry information. It is
        issued from binary files holding field information. It is set to
        None if not available for this time step.