Static method. Check whether a set of convex polygons are all 
		contiguous. Two polygons are considered contiguous if they 
		share, at least, one side (two vertices).
        
        This is not a complete verification, it is a very simplified
        one. For a given set of polygons this method will verify that 
        the number of common vertices among them equals or exceeds the
        minimum number of common vertices possible.
        
        This little algorithm will not declare a contiguous set of 
        polygons as non-contiguous, but it can fail in the reverse for 
        certain geometries where polygons have several common vertices
        among them.
        
        :param polygons: List of polygons.
        :type polygons: list of ``pyny.Polygon``
        :return: Whether tey are contiguous.
        :rtype: bool

def contiguous(polygons):
        """
        Static method. Check whether a set of convex polygons are all 
		contiguous. Two polygons are considered contiguous if they 
		share, at least, one side (two vertices).
        
        This is not a complete verification, it is a very simplified
        one. For a given set of polygons this method will verify that 
        the number of common vertices among them equals or exceeds the
        minimum number of common vertices possible.
        
        This little algorithm will not declare a contiguous set of 
        polygons as non-contiguous, but it can fail in the reverse for 
        certain geometries where polygons have several common vertices
        among them.
        
        :param polygons: List of polygons.
        :type polygons: list of ``pyny.Polygon``
        :return: Whether tey are contiguous.
        :rtype: bool
        """
        from pyny3d.utils import sort_numpy
        
        n = len(polygons)
        points = sort_numpy(np.concatenate([polygon.points 
                                            for polygon in polygons]))
        diff = np.sum(np.diff(points, axis=0), axis=1)
        if sum(np.isclose(diff, 0)) < n*2-2:
            return False
        else:
            return True