An efficient algorithm for the 1D total Visibility-Index problem

M.T. de Berg, P. Afshani, H. Casanovaz, B. Karsin, C. Lambrechts, N. Sitchinavaz, C. Tsirogiannis

Onderzoeksoutput: Hoofdstuk in Boek/Rapport/CongresprocedureConferentiebijdrageAcademicpeer review

4 Citaten (Scopus)

Samenvatting

Let T be a terrain, and let P be a set of points (locations) on its surface. An important problem in Geographic Information Science (GIS) is computing the visibility index of a point p on P, that is, the number of points in P that are visible from p. The total visibility-index problem asks for computing the visibility index of every point in P. Most applications of this problem involve 2-dimensional terrains represented by a grid of n × n square cells, where each cell is associated with an elevation value, and P consists of the center-points of these cells. Current approaches for computing the total visibility- index on such a terrain take at least quadratic time with respect to the number of the terrain cells. While finding a subquadratic solution to this 2D total visibility-index problem is an open problem, surprisingly, no subquadratic solution has been proposed for the one-dimensional (1D) version of the problem; in the 1D problem, the terrain is an x-monotone polyline, and P is the set of the polyline vertices. We present an O(n log 2 n) algorithm that solves the 1D total visibility-index problem in the RAM model. Our algorithm is based on a geometric dual-ization technique, which reduces the problem into a set of instances of the red-blue line segment intersection counting problem. We also present a parallel version of this algorithm, which requires O(log 2 n) time and O(n log 2 n) work in the CREW PRAM model. We implement a naive O(n 2) approach and three variations of our algorithm: one employing an existing red-blue line segment intersection algorithm and two new approaches that perform the intersection counting by leveraging features specific to our problem. We present experimental results for both serial and parallel implementations on large synthetic and real-world datasets, using two distinct hardware platforms. Results show that all variants of our algorithm outperform the naive approach by several orders of magnitude on large datasets. Furthermore, we show that our new inter- section counting implementations achieve more than 8 times speedup over the existing red-blue line segment intersection algorithm. Our parallel implementation is able to process a terrain of 2 24 vertices in under 1 minute using 16 cores, achieving more than 7 times speedup over serial execution.

Originele taal-2Engels
Titel2017 Proceedings of the Ninteenth Workshop on Algorithm Engineering and Experiments (ALENEX)
RedacteurenSándor Fekete, Vijava Ramachandran
UitgeverijSociety for Industrial and Applied Mathematics (SIAM)
Pagina's218-231
Aantal pagina's14
ISBN van elektronische versie978-1-61197-476-8
DOI's
StatusGepubliceerd - 2017
Evenement19th Workshop on Algorithm Engineering and Experiments (ALENEX 2017) - Hotel Porta Fira, Barcelona, Spanje
Duur: 17 jan. 201718 jan. 2017
Congresnummer: 19
https://www.siam.org/meetings/alenex17/

Congres

Congres19th Workshop on Algorithm Engineering and Experiments (ALENEX 2017)
Verkorte titelALENEX 2017
Land/RegioSpanje
StadBarcelona
Periode17/01/1718/01/17
Internet adres

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