Interact with segy in depth slice mode (fixed z-coordinate)

        Returns
        -------
        depth : Depth

        Notes
        -----
        .. versionadded:: 1.1

        .. versionchanged:: 1.7.1
            enabled for unstructured files

def depth_slice(self):
        """
        Interact with segy in depth slice mode (fixed z-coordinate)

        Returns
        -------
        depth : Depth

        Notes
        -----
        .. versionadded:: 1.1

        .. versionchanged:: 1.7.1
            enabled for unstructured files
        """

        if self.depth is not None:
            return self.depth

        from .depth import Depth
        self.depth = Depth(self)
        return self.depth