Showing papers on "Computational geometry published in 1982"

Linear-time algorithms for linear programming in R3 and related problems

Abstract: Linear-time for Linear Programming in R2 and R3 are presented. The methods used are applicable for some other problems. For example, a linear-time algorithm is given for the classical problem of finding the smallest circle enclosing n given points in the plane. This disproves a conjecture by Shamos and Hoey that this problem requires Ω(n log n) time. An immediate consequence of the main result is that the problem of linear separability is solvable in linear-time. This corrects an error in Shamos and Hoey's paper, namely, that their O(n log n) algorithm for this problem in the plane was optimal. Also, a linear-time algorithm is given for the problem of finding the weighted center of a tree and algorithms for other common location-theoretic problems are indicated. The results apply also to the problem of convex quadratic programming in three-dimensions. The results have already been extended to higher dimensions and we know that linear programming can be solved in linear-time when the dimension is fixed. This will be reported elsewhere; a preliminary report is available from the author.

Plane-sweep algorithms for intersecting geometric figures

Abstract: Algorithms in computational geometry are of increasing importance in computer-aided design, for example, in the layout of integrated circuits. The efficient computation of the intersection of several superimposed figures is a basic problem. Plane figures defined by points connected by straight line segments are considered, for example, polygons (not necessarily simple) and maps (embedded planar graphs). The regions into which the plane is partitioned by these intersecting figures are to be processed in various ways such as listing the boundary of each region in cyclic order or sweeping the interior of each region. Let m be the total number of points of all the figures involved and s be the total number of intersections of all line segments. A two plane-sweep algorithm that solves the problems above is presented; in the general case (non convexity) in time O((n+s)log-n) and space O(n+s); when the regions of each given figure are convex, the same can be achieved in time O(n log n +s) and space O(n)

The EXCELL Method for Efficient Geometric Access to Data

Abstract: The extendible cell (EXCELL) method provides a data structure for efficient geometric access. It stores geometric data into computer storage blocksm corresponding to disjoint variable sized rectangular cells accessible by an address calculation type directory. We describe the method for point files and files of more complicated figures analyzing performance. We report algorithms for the nearest neighbour and point-in-polygon-network problems and describe applications to geographical data bases, hidden line elimination and geometric modeling.

Computing Point Enclosures

Abstract: Given a set of n rectangles in the plane, the point enclosure query is the question to determine for any point p which rectangles of the set it is contained in. It is the "dual" of the well-known range query in computational geometry. It is shown that the point enclosure query in the plane can be answered in 0(log n + k) time, where k is the number of rectangles reported. The solution makes use of a new data structure, called the S-tree. The data structure can be generalized to obtain an efficient algorithm for the point enclosure problem in d-dimensional space d ≥ 2.

A Computational Geometry for the Blades and Internal Flow Channels of Centrifugal Compressors

Abstract: A new computational geometry for the blades and internal flow passages of centrifugal compressors is described and examples of its use in the design of industrial compressors are given. The method makes use of Bernstein-Bezier polynomial patches to define the geometrical shape of the flow channels. This has the following main advantages: the surfaces are defined by analytic functions which allow systematic and controlled variation of the shape and give continuous derivatives up to any required order; and the parametric form of the equations allows the blade and channel coordinates to be very simply obtained at any number of points and in any suitable distribution for use in subsequent aerodynamic and stress calculations and for manufacture. The method is particularly suitable for incorporation into a computer aided design procedure.Copyright © 1982 by ASME

Application of computational geometry to pattern recognition problems

Abstract: In this thesis it is shown that several pattern recognition problems can be solved efficiently by exploiting the geometrical structure of the problems. The problems considered are in the area of clustering and classification. These problems are: (i) computing the diameter of a finite planar set, (ii) computing the maximum and minimum distance between two finite planar sets of points, (iii) testing for point inclusion in a convex polyhedron in d-dimensional space, and (iv) exact and inexact reference set thinning for the nearest neighbor decision rule. Algorithms to solve the above problems are presented and analyzed for worst-case and average-case situations. These algorithms are implemented and experimentally compared with the existing algorithms. In solving the above problems, a geometrical construct, known as the Voronoi diagram is used extensively. However, there exists no practical algorithm to construct the Voronoi diagram in d dimensional spaces when d > 2. In this thesis an efficient algorithm to construct the Voronoi diagram in d-space is presented.