Triangulation is the division of a surface or plane polygon into a set of triangles, usually with the restriction that each triangle side
is entirely shared by two adjacent triangles. It was
proved in 1925 that every surface has a triangulation, but it might require an infinite
number of triangles and the proof is difficult (Francis
and Weeks 1999). A surface with a finite number of triangles in its triangulation
is called compact.
Wickham-Jones (1994) gives an algorithm for triangulation ("otectomy"), and
O'Rourke (1998, p. 47) sketches a method for improving this to , as first done by Lennes (1911). Garey et al. (1978)
gave an algorithmically straightforward method for triangulation, which was for many years believed
optimal. However, Tarjan and van Wyk (1988) produced an algorithm. This was followed by an unexpected result
due to Chazelle (1991), who showed that an arbitrary simple
polygon can be triangulated in . However, according to Skiena (1997), "this algorithm
is quite hopeless to implement."