Write the grid points to the GMSH-command file.

        Parameters
        ----------
        fid: file object for the command file (.geo)

def write_points(self, fid):
        """
        Write the grid points to the GMSH-command file.

        Parameters
        ----------
        fid: file object for the command file (.geo)

        """
        for nr, point in enumerate(self.Points):
            fid.write(
                'Point({0}) = {{{1}, {2}, 0, {3}}};\n'.format(
                    nr + 1, point[0], point[1], self.Charlengths[nr]))