def surface_nodes(self):
        """
        :param points: a list of Point objects
        :returns: a Node of kind 'griddedSurface'
        """
        line = []
        for point in self.mesh:
            line.append(point.longitude)
            line.append(point.latitude)
            line.append(point.depth)
        return [Node('griddedSurface', nodes=[Node('gml:posList', {}, line)])]
:param points: a list of Point objects
        :returns: a Node of kind 'griddedSurface'