def inverse_transform(self, maps):
        """ This function transforms from cartesian to spherical spins.

        Parameters
        ----------
        maps : a mapping object

        Returns
        -------
        out : dict
            A dict with key as parameter name and value as numpy.array or float
            of transformed values.
        """
        sx, sy, sz = self._outputs
        data = coordinates.cartesian_to_spherical(maps[sx], maps[sy], maps[sz])
        out = {param : val for param, val in zip(self._outputs, data)}
        return self.format_output(maps, out)