193 research outputs found

    Canonical ordering for graphs on the cylinder, with applications to periodic straight-line drawings on the flat cylinder and torus

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    We extend the notion of canonical ordering (initially developed for planar triangulations and 3-connected planar maps) to cylindric (essentially simple) triangulations and more generally to cylindric (essentially internally) 33-connected maps. This allows us to extend the incremental straight-line drawing algorithm of de Fraysseix, Pach and Pollack (in the triangulated case) and of Kant (in the 33-connected case) to this setting. Precisely, for any cylindric essentially internally 33-connected map GG with nn vertices, we can obtain in linear time a periodic (in xx) straight-line drawing of GG that is crossing-free and internally (weakly) convex, on a regular grid Z/wZ×[0..h]\mathbb{Z}/w\mathbb{Z}\times[0..h], with w≤2nw\leq 2n and h≤n(2d+1)h\leq n(2d+1), where dd is the face-distance between the two boundaries. This also yields an efficient periodic drawing algorithm for graphs on the torus. Precisely, for any essentially 33-connected map GG on the torus (i.e., 33-connected in the periodic representation) with nn vertices, we can compute in linear time a periodic straight-line drawing of GG that is crossing-free and (weakly) convex, on a periodic regular grid Z/wZ×Z/hZ\mathbb{Z}/w\mathbb{Z}\times\mathbb{Z}/h\mathbb{Z}, with w≤2nw\leq 2n and h≤1+2n(c+1)h\leq 1+2n(c+1), where cc is the face-width of GG. Since c≤2nc\leq\sqrt{2n}, the grid area is O(n5/2)O(n^{5/2}).Comment: 37 page
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