Solar activity is characterized by complex dynamics superimposed onto an almost periodic, approximately 11-year cycle. One of its main features is the presence of a marked, time-varying hemispheric asymmetry, the deeper reasons for which have not yet been completely uncovered. Traditionally, this asymmetry has been studied by considering amplitude and phase differences. Here, we use visibility ...

In general, visibility reconstruction problems involve determining a set of objects in the plane that exhibit a speci ed set of visibility constraints. In this paper, an algorithm for reconstructing a set of parallel line segments is presented, from speci ed visibility information contained in an extended endpoint visibility graph. The algorithm runs in polynomial time and relies on simple vect...

In this paper, we give a characterization of the visibility graphs of pseudo-polygons. We first identify some key combinatorial properties of pseudo-polygons, and we then give a set of five necessary conditions based off our identified properties. We then prove that these necessary conditions are also sufficient via a reduction to a characterization of vertex-edge visibility graphs given by O’R...

The problem of aggregation is considerable importance in many disciplines. In this paper, a new type of operator called visibility graph averaging (VGA) aggregation operator is proposed. This proposed operator is based on the visibility graph which can convert a time series into a graph. The weights are obtained according to the importance of the data in the visibility graph. Finally, the VGA o...

Let P be a simple polygon with n vertices. We present a new O(n)-time algorithm to compute the visible part of one edge from another edge of P . The algorithm does not alter the input and only uses O(1) variables and is therefore a constant-workspace algorithm. The algorithm can be used to make a constant-workspace algorithm for computing the weak visibility polygon from an edge in O(mn) time, ...

The visibility graph V(X) of a discrete point set X ⊂ R has vertex set X and an edge xy for every two points x, y ∈ X whenever there is no other point in X on the line segment between x and y. We show that for every graphG, there is a point setX ∈ R, such that the subgraph of V(X∪Z) induced by X is isomorphic to G. As a consequence, we show that there are visibility graphs of arbitrary high chr...

We present a lighting method for outdoor scenes with vegetation. The method is compatible with multiresolution trees generated using random L-systems. We include a sky dome model that gets the luminance and chromaticity values at several sampling points for different time and location. The samples are used to compute the light arriving to the objects in the scene depending on the insolation con...

Several recent image compression standards rely upon the Discrete Cosine Transform (DCT). Models of DCT basis function visibility can be used to design quantization matrices for arbitrary viewing conditions and images. Here we report new results on the effects of viewing distance and contrast masking on basis function visibility. We measured contrast detection thresholds for DCT basis functions...

Vernier acuity is susceptible to degradation by image motion. The purpose of this study was to determine to what extent vernier thresholds are elevated in the presence of image motion because of reduced stimulus visibility, due to contrast smearing, or to a shift in the spatial scale of analysis. To test the visibility hypothesis, we measured vernier thresholds as a function of stimulus velocit...