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On the number of radial orderings of colored planar point sets. (English) Zbl 1374.68661
Márquez, Alberto (ed.) et al., Computational geometry. XIV Spanish meeting on computational geometry, EGC 2011, dedicated to Ferran Hurtado on the occasion of his 60th birthday, Alcalá de Henares, Spain, June 27–30, 2011. Revised selected papers. Berlin: Springer (ISBN 978-3-642-34190-8/pbk). Lecture Notes in Computer Science 7579, 109-118 (2012).
Summary: Let $$n$$ be an even natural number and let $$S$$ be a set of $$n$$ red and $$n$$ blue points in general position in the plane. Let $$p \notin S$$ be a point such that $$S \cup \{p\}$$ is in general position. A radial ordering of $$S$$ with respect to $$p$$ is a circular ordering of the elements of $$S$$ by angle around $$p$$. A colored radial ordering is a radial ordering of $$S$$ in which only the colors of the points are considered. We show that: the number of distinct radial orderings of $$S$$ is at most $$O(n^{4})$$ and at least $$\Omega (n^{2})$$; the number of colored radial orderings of $$S$$ is at most $$O(n^{4})$$ and at least $$\Omega (n)$$; there exists sets of points with $$\Theta (n^{4})$$ colored radial orderings and sets of points with only $$O(n^{2})$$ colored radial orderings.
For the entire collection see [Zbl 1253.68016].
##### MSC:
 68U05 Computer graphics; computational geometry (digital and algorithmic aspects)
##### Keywords:
radial orderings; colored point sets; star polygonizations
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##### References:
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