@article {IOPORT.06111131, author = {L\"offler, Maarten and Mulzer, Wolfgang}, title = {Triangulating the square and squaring the triangle: quadtrees and Delaunay triangulations are equivalent.}, year = {2012}, journal = {SIAM Journal on Computing}, volume = {41}, number = {4}, issn = {0097-5397}, pages = {941-974}, publisher = {Society for Industrial and Applied Mathematics (SIAM), Philadelphia, PA}, doi = {10.1137/110825698}, abstract = {Summary: We show that Delaunay triangulations and compressed quadtrees are equivalent structures. More precisely, we give two algorithms: the first computes a compressed quadtree for a planar point set, given the Delaunay triangulation; the second finds the Delaunay triangulation, given a compressed quadtree. Both algorithms run in deterministic linear time on a pointer machine. Our work builds on and extends previous results by Krznaric and Levcopolous and Buchin and Mulzer. Our main tool for the second algorithm is the well-separated pair decomposition (WSPD), a structure that has been used previously to find Euclidean minimum spanning trees in higher dimensions. We show that knowing the WSPD (and a quadtree) suffices to compute a planar Euclidean minimum spanning tree (EMST) in linear time. With the EMST at hand, we can find the Delaunay triangulation in linear time. As a corollary, we obtain deterministic versions of many previous algorithms related to Delaunay triangulations, such as splitting planar Delaunay triangulations, preprocessing imprecise points for faster Delaunay computation, and transdichotomous Delaunay triangulations.}, identifier = {06111131}, }