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Guarding Polyhedral Terrains
, 1992
"... We prove that b c vertex guards are always sufficient and sometimes necessary to guard the surface of an nvertex polyhedral terrain. We also show that b guards are sometimes necessary to guard the surface of an nvertex polyhedral terrain. ..."
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Cited by 26 (6 self)
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We prove that b c vertex guards are always sufficient and sometimes necessary to guard the surface of an nvertex polyhedral terrain. We also show that b guards are sometimes necessary to guard the surface of an nvertex polyhedral terrain.
Feasibility of Design in Stereolithography
, 1993
"... We study the feasibility of design for a layerdeposition manufacturing process called stereolithography which works by controlling a vertical laser beam which when targeted on a photocurable liquid causes the liquid to harden. In order to better understand the power as well as the limitations o ..."
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Cited by 15 (4 self)
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We study the feasibility of design for a layerdeposition manufacturing process called stereolithography which works by controlling a vertical laser beam which when targeted on a photocurable liquid causes the liquid to harden. In order to better understand the power as well as the limitations of this manufacturing process, we define a mathematical model of stereolithography (referred to as vertical stereolithography) and analyze the class of objects that can be constructed under the assumptions of the model. Given an object (modelled as a polygon or a polyhedron), we give algorithms that decide in O(n) time (where n is the number of vertices in the polygon or polyhedron) whether or not the object can be constructed by vertical stereolithography. If the answer is in the affirmative, the algorithm reports a description of all the orientations in which the object can be made. We also show that the objects built with vertical stereolithography are precisely those that can be made with a 3axis NC machine.
Approximating the visible region of a point on a terrain
 In Proc. Algorithm Engineering and Experiments (ALENEX’04), accepted
, 2004
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Exploring multiple viewshed analysis using terrain features and optimisation techniques
 Computers & Geosciences
, 2004
"... The calculation of viewsheds is a routine operation in GIS and is used in a wide range of applications. Many of these involve the siting of features, such as radio masts, which are part of a network and yet the selection of sites is normally done separately for each feature. The selection of a serie ..."
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Cited by 8 (0 self)
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The calculation of viewsheds is a routine operation in GIS and is used in a wide range of applications. Many of these involve the siting of features, such as radio masts, which are part of a network and yet the selection of sites is normally done separately for each feature. The selection of a series of locations which collectively maximise the visual coverage of an area is a combinatorial problem and as such cannot be directly solved except for trivial cases. In this paper, two strategies for tackling this problem are explored. The first is to restrict the search to key topographic points in the landscape such as peaks, pits and passes. The second is to use heuristics which have been applied to other maximal coverage spatial problems such as locationallocation. The results show that the use of these two strategies results in a reduction of the computing time necessary by two orders of magnitude, but at the cost of a loss of ten percent in the area viewed. Three different heuristics were used, of which Simulated Annealing produced the best results. However the improvement over a much simpler fastdescent swap heuristic was very slight, but at the cost of greatly increased running times.
WorstCaseOptimal Algorithms for Guarding Planar Graphs and Polyhedral Surfaces
, 2003
"... We present an optimal \Theta (n)time algorithm for the selection of a subset of the vertices of an nvertex plane graph G so that each of the faces of G is covered by (i.e. incident with) one or more of the selected vertices. At most bn=2c vertices are selected, matching the worstcase requiremen ..."
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Cited by 6 (0 self)
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We present an optimal \Theta (n)time algorithm for the selection of a subset of the vertices of an nvertex plane graph G so that each of the faces of G is covered by (i.e. incident with) one or more of the selected vertices. At most bn=2c vertices are selected, matching the worstcase requirement. Analogous results for edgecovers are developed for two different notions of &quot;coverage&quot;. In particular,our lineartime algorithm selects at most n \Gamma 2 edges to strongly cover G, at most bn=3c diagonals to cover G, and in the case where G has no quadrilateral faces, at most bn=3c edges to cover G. All these bounds are optimal in the worstcase. Most of our results flow from the study of a relaxation of thefamiliar notion of a 2coloring of a plane graph which we call a facerespecting 2coloring that permits
Survey and Analysis of Multimodal Sensor Planning and Integration for Wide Area Surveillance
"... Although sensor planning in computer vision has been a subject of research for over two decades, a vast majority of the research seems to concentrate on two particular applications in a rather limited context of laboratory and industrial workbenches, namely 3D object reconstruction and robotic arm m ..."
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Cited by 5 (0 self)
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Although sensor planning in computer vision has been a subject of research for over two decades, a vast majority of the research seems to concentrate on two particular applications in a rather limited context of laboratory and industrial workbenches, namely 3D object reconstruction and robotic arm manipulation. Recently, increasing interest is engaged in research to come up with solutions that provide widearea autonomous surveillance systems for object characterization and situation awareness, which involves portable, wireless, and/or Internet connected radar, digital video, and/or infrared sensors. The prominent research problems associated with multisensor integration for widearea surveillance are modality selection, sensor planning, data fusion, and data exchange (communication) among multiple sensors. Thus, the requirements and constraints to be addressed include farfield view, wide coverage, high resolution, cooperative sensors, adaptive sensing modalities, dynamic objects, and uncontrolled environments. This article summarizes a new survey and analysis conducted in light of these challenging requirements and constraints. It involves techniques and strategies from work done in the areas of sensor fusion, sensor networks, smart sensing, Geographic Information Systems (GIS), photogrammetry, and other intelligent systems where finding optimal solutions to the placement and deployment of multimodal sensors covering a wide area is important. While techniques covered in this survey are applicable to many widearea environments such as traffic monitoring,
Efficient Algorithms for Guarding or Illuminating the Surface of a Polyhedral Terrain
 Proceedings of the 8th Canadian Conference on Computational Geometry, volume 5 of International Informatics Series
, 1996
"... We present efficient polynomial time algorithms that place bn=2c vertex guards which cover the surface of an nvertex polyhedral terrain, and similarly, bn=3c edge guards which cover the surface of an nvertex polyhedral terrain. The time complexity of both algorithms, dominated by the cost of fi ..."
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Cited by 5 (0 self)
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We present efficient polynomial time algorithms that place bn=2c vertex guards which cover the surface of an nvertex polyhedral terrain, and similarly, bn=3c edge guards which cover the surface of an nvertex polyhedral terrain. The time complexity of both algorithms, dominated by the cost of finding a maximum matching in a graph, is O(n ).
Parallelizing Visibility Computations on Triangulated Terrains
 International Journal of Geographical Information Systems
, 1994
"... In this paper we address the problem of computing visibility information on digital terrain models in parallel. We propose a parallel algorithm for computing the visible region of an observation point located on the terrain. The algorithm is based on a sequential trianglesorting visibility approach ..."
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Cited by 3 (0 self)
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In this paper we address the problem of computing visibility information on digital terrain models in parallel. We propose a parallel algorithm for computing the visible region of an observation point located on the terrain. The algorithm is based on a sequential trianglesorting visibility approach proposed in [De Floriani et al. 1989]. Static and dynamic parallelization strategies, both in terms of partitioning criteria and scheduling policies, are discussed. The different parallelization strategies are implemented on an MIMD multicomputer and evaluated through experimental results.
, Thanh Tung Nguyen
"... 1 Search and Surveillance in emergency situations – A GISbased approach to construct optimal visibility graphs ..."
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1 Search and Surveillance in emergency situations – A GISbased approach to construct optimal visibility graphs
FOR
, 2005
"... I certify that this thesis satisfies all the requirements as a thesis for the degree of ..."
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I certify that this thesis satisfies all the requirements as a thesis for the degree of