Returns the number of edges in the convex hull.
            Useful for identifying catalytically active sites.

def tot_edges(self):
        """
        Returns the number of edges in the convex hull.
            Useful for identifying catalytically active sites.
        """
        all_edges = []
        for facet in self.facets:
            edges = []
            pt = self.get_line_in_facet(facet)

            lines = []
            for i, p in enumerate(pt):
                if i == len(pt) / 2:
                    break
                lines.append(tuple(sorted(tuple([tuple(pt[i*2]), tuple(pt[i*2+1])]))))

            for i, p in enumerate(lines):
                if p not in all_edges:
                    edges.append(p)

            all_edges.extend(edges)

        return len(all_edges)