Everett et al. [EHN96, EHN97] introduced several varieties of stabbing information for the lines determined by pairs of vertices of a simple polygon P , and established their relationships to vertex visibility and other combinatorial data. In the same spirit, we define the “zero-parity (ZP) stabbing information” to be a natural weakening of their “weak stabbing information,” retaining only the ...

A visibility relation can be viewed as a graph: the uncountable graph of a visibility relationship between points in a polygon P is called the point visibility graph (PVG) of P. In this paper we explore the use of perfect graphs to characterize tractable subprob-lems of visibility problems. Our main result is a characterization of which polygons are guaranteed to have weakly triangulated PVGs, ...

results there was no significant differences between if and conventional mode regarding visibility of mic (p > 0.05). conclusion although using if caused improved visibility of mic, the difference with conventional mode was not statistically different. patients and methods in this cross-sectional study, 2580 digital panoramic images of 18 to 70-year-old patients were inspected for presence of m...

(a) (b) Figure 8: The nal set of directions from that covers G S in thick gray lines. Two views are provided with (a) presents the regular view of Figures 5 to 7 and (b) shows the entire Gauss map. See also Figure 1. (a) (b) Figure 6: The boundary and central silhouettes of G S in thick dark gray lines is projected onto the plane z = 1 in thick light gray lines, in (a). In (b), The convex hull ...

the islamic calendar is based on lunar months, which begin when the thin crescent moon is actually sighted in the western sky after sunset within a day or so after the new moon. the islamic dates begin at sunset on the previous day. the visibility of the lunar crescent as a function of the moon's age - the time counted from the new moon - is obviously of great importance to muslims. the da...

Given a simple polygon P in the plane, we present new algorithms and data structures for computing the weak visibility polygon from any query line segment in P . We build a data structure in O(n) time and O(n) space that can compute the visibility polygon for any query line segment s in O(k log n) time, where k is the size of the visibility polygon of s and n is the number of vertices of P . Al...

Unit square (grid) visibility graphs (USV and USGV, resp.) are described by axisparallel visibility between unit squares placed (on integer grid coordinates) in the plane. We investigate combinatorial properties of these graph classes and the hardness of variants of the recognition problem, i. e., the problem of representing USGV with fixed visibilities within small area and, for USV, the gener...

We analyze how to efficiently maintain and update the visibility polygons for a segment observer moving in a polygonal domain. The space and time requirements for preprocessing are O(n) and after preprocessing, visibility change events for weak and strong visibility can be handled in O(log |VP|) and O(log(|VP1| + |VP2|)) respectively, or O(log n) in which |VP| is the size of the line segment’s ...