Algorithms for ε-Approximations of Terrains

  • Authors:
  • Jeff M. Phillips

  • Affiliations:
  • Department of Computer Science, Duke University, Durham, NC 27708

  • Venue:
  • ICALP '08 Proceedings of the 35th international colloquium on Automata, Languages and Programming, Part I
  • Year:
  • 2008

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Abstract

Consider a point set ${\mathcal{D}}$ with a measure function$\mu : {\mathcal{D}} \to \mathcal{R}$. Let ${\mathcal{A}}$ be theset of subsets of $\mathcal{D}$ induced by containment in a shapefrom some geometric family (e.g. axis-aligned rectangles, halfplanes, balls, k-oriented polygons). We say a range space$(\mathcal{D}, \mathcal{A})$ has anε-approximation P if$$\max_{R \in \mathcal{A}} \left| \frac{\mu(R \cap P)}{ \mu(P)}- \frac{\mu(R \cap \mathcal{D})}{ \mu(\mathcal{D})} \right| \leq\varepsilon.$$We describe algorithms for deterministically constructingdiscrete µ-approximations for continuous point setssuch as distributions or terrains. Furthermore, for certainfamilies of subsets $\mathcal{A}$, such as those described byaxis-aligned rectangles, we reduce the size of theε-approximations by almost a square root from$O(\frac{1}{\varepsilon^2} \log \frac{1}{\varepsilon})$ to . Thisis often the first step in transforming a continuous problem into adiscrete one for which combinatorial techniques can be applied. Wedescribe applications of this result in geospatial analysis,biosurveillance, and sensor networks.