Computing a canonical polygonal schema of an orientable triangulated surface

A closed orientable surface of genus g can be obtained by appropriat e identification of pairs of edges of a $4g$-gon (the polygonal schema). The identified edges form $2g$ loops on the surface, that are disjoint except for their common end-point. These loops are generators of both the fundamental group and the homology group of the surface. The inverse problem is concerned with finding a set of $2g$ loops on a triangulated surface, such that cutting the surface along these loops yields a (canonical) polygonal schema. We present two optimal algorithms for this inverse problem. Both algorithms have been implemented using the CGAL polyhedron data structure.