3-Colored Triangulation of 2D Maps
We describe an algorithm to triangulate a general map on an arbitrary surface in such way that the resulting triangulation is vertex-colorable with three colors. (Three-colorable triangulations can be efficiently represented and manipulated by the GEM data structure of Montagner and Stolfi.) The standard solution to this problem is the barycentric subdivision, which produces [Formula: see text] triangles when applied to a map with [Formula: see text] edges, such that [Formula: see text] of them are border edges (adjacent to only one face). Our algorithm yields a subdivision with at most [Formula: see text] triangles, where [Formula: see text] is the Euler Characteristic of the surface; or at most [Formula: see text] triangles if all [Formula: see text] faces of the map have the same degree [Formula: see text]. Experimental results show that the resulting triangulations have, on the average, significantly fewer triangles than these upper bounds.