Abstract:This paper studies the point location problem in Delaunay triangulations without preprocessing and additional storage. The proposed procedure finds the query point by simply "walking through" the triangulation, after selecting a "good starting point" by random sampling. The analysis generalizes and extends a recent result for d = 2 dimensions by proving this procedure takes expected time close to O(n 1/(d+1)) for point location in Delaunay triangulations of n random points in d = 3 dimensions. Empirical result… Show more
“…This "point location problem", which is a standard problem in geographic information systems and computer-aided design and engineering [74], is the most time consuming part. However, the number of tagged elements (which are cut by the slice plane) is usually far smaller than the total number of elements, and so we can use a brute force yet clever approach, which takes advantage of some peculiarities of our specific problem.…”
“…This "point location problem", which is a standard problem in geographic information systems and computer-aided design and engineering [74], is the most time consuming part. However, the number of tagged elements (which are cut by the slice plane) is usually far smaller than the total number of elements, and so we can use a brute force yet clever approach, which takes advantage of some peculiarities of our specific problem.…”
“…The first application is the randomized incremental construction of the Delaunay Triangulation using the Jump-andWalk strategy, introduced by Mücke, Zhu et al [12], [13]. This strategy proceeds in an incremental way.…”
Section: Convex Hull (2d-hull) and The Construction Of The Twodimensmentioning
Robustness is a key issue on any runtime system that aims to speed up the execution of a program. However, robustness considerations are commonly overlooked when new software-based, thread-level speculation (STLS) systems are proposed. This paper highlights the relevance of the problem, showing different situations when the use of incorrect data can irreversibly alter the speculative execution of an algorithm, despite the efforts of a given STLS system to maintain sequential consistency. We show that the management of speculative exceptions is a common factor to these problems. Based on this fact, we propose a novel solution to handle speculative exceptions. Our solution eagerly tries to solve the issue before the non-speculative thread arrives to the instruction that rose the exception. We compare our solution to a more conservative approach found in the bibliography. The comparison is done both qualitatively, through a detailed analysis of the tradeoffs involved, and quantitatively, evaluating the effects of both solutions in the execution of three different benchmarks on a real system. Both studies conclude that our solution handles the occurrence of speculative exceptions more efficiently. Under heavy loads intended to push to its limits a STLS system, our solution leads to execution times reduced by up to 52.02% with respect to earlier proposals. Our solution does not affect the performance when speculative exceptions do not appear. We believe that our proposal makes STLS systems robust enough to be used in production environments.
“…To know the value of a given attribute at a location x, one simply has to find the cell containing x- Mücke et al (1999) describe an efficient way to achieving that.…”
Fields as found in the geosciences have properties that are not usually found in other disciplines: the phenomena studied are often three-dimensional, they tend to change continuously over time, and the collection of samples to study the phenomena is problematic, which often results in highly anisotropic distributions of samples. In the GIS community, raster structures (voxels or octrees) are the most popular solutions, but, as we show in this paper, they have shortcomings for modelling and analysing 3D geoscientific fields. As an alternative to using rasters, we propose a new spatial model based on the Voronoi diagram (VD) and its dual the Delaunay tetrahedralization (DT), and argue that they have many advantages over other tessellations. We discuss the main properties of the 3D VD/DT, present some GIS operations that are greatly simplified when the VD/DT is used, and, to analyse two or more fields, we also present a variant of the map algebra framework where all the operations are performed directly on VDs. The usefulness of this Voronoi-based spatial model is demonstrated with a series of potential applications.
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