A visibility representation of a graph G is an assignment of the vertices of G to geometric objects such that vertices are adjacent if and only if their corresponding objects are “visible” each other, that is, there is an uninterrupted channel, usually axis-aligned, between them. Depending on the objects and definition of visibility used, not all graphs are visibility graphs. In such situations...

Given an arbitrary polygon P with holes, we construct a polytopal complex analogous to the associahedron based on convex diagonalizations of P . This polytopal complex is shown to be contractible, and a geometric realization is provided based on the theory of secondary polytopes. We then reformulate a combinatorial deformation theory and present an open problem based on visibility which is a cl...

We exhibit a family of graphs which can be realized as pseudo-visibility graphs of pseudo-polygons, but not of straight-line polygons. The example is based on the characterization of vertex-edge pseudo-visibility graphs of O’Rourke and Streinu [Proc. ACM Symp. Comput. Geometry, Nice, France, 1997, pp. 119–128] and extends a recent result of the author [Proc. ACM Symp. Comput. Geometry, Miami Be...

Visibility is an important factor of environmental quality that has various influences on the quality of neighborhood. This paper aimed to find the relationship between urban form and visual quality. A public space with a spatial configuration in one of Bushehr city's neighborhoods was selected as the case study. Bushehr city is surrounded by urban development and the sea. Compact urban spac...

conclusion the dwmri is a useful technique for evaluating activity of fistulas with abscess. perianal fistula visibility is greater with combined t2wi and dwmri than t2wi alone. patients and methods fifty-three patients with 56 perianal fistulas were included in the current retrospective study. the t2-weighted imaging (t2wi) and dwmri were performed and apparent diffusion coefficient (adc) valu...

This paper describes a new algorithm that employs image-based rendering for fast occlusion culling in complex urban environments. It exploits graphics hardware to render and automatically combine a relatively large set of occluders. The algorithm is fast to calculate and therefore also useful for scenes of moderate complexity and walkthroughs with over 20 frames per second. Occlusion is calcula...

This paper surveys recent studies of learning problems in which the learner faces restrictions on the amount of information he can extract from each example he encounters. Our main framework for the analysis of such scenarios is the RFA (Restricted Focus of Attention) model. While being a natural reenement of the PAC learning model, some of the fundamental PAC-learning results and techniques fa...

We consider direct visibility in simple orthogonal polygons and derive tight lower and upper bounds on the number of strictly internal and external visibility edges. We also show a lower bound of ⌈n2 ⌉ − 1 on the number of diffuse reflections required for completely illuminating an orthogonal polygon from an arbitrary point inside it. Further, we derive lower bounds on the combinatorial complex...

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We study polar visibility graphs, graphs whose vertices can be represented by arcs of concentric circles with adjacency determined by radial visibility including visibility through the origin. These graphs are more general than the well-studied bar-visibility graphs and are characterized here, when arcs are proper subsets of circles, as the graphs that embed on the plane with all but at most on...