Exploratory Spectral Analysis in Three-Dimensional Spatial Point Patterns

Abstract

A spatial point pattern is a collection of points irregularly located within a bounded area (2D) or space (3D) that have been generated by some form of stochastic mechanism. Examples of point patterns include locations of trees in a forest, of cases of a disease in a region, or of particles in a microscopic section of a composite material. Spatial Point pattern analysis is used mostly to determine the absence (completely spatial randomness) or presence (regularity and clustering) of spatial dependence structure of the locations. Methods based on the space domain are widely used for this purpose, while methods conducted in the frequency domain (spectral analysis) are still unknown to most researchers. Spectral analysis is a powerful tool to investigate spatial point patterns, since it does not assume any structural characteristics of the data (ex. isotropy), and uses only the autocovariance function, and its Fourier transform. There are some methods based on the spectral frameworks for analyzing 2D spatial point patterns. There is no such methods available for the 3D situation and, therefore, the aim of this work is to develop new methods based on spectral framework for the analysis of three-dimensional point patterns. The emphasis is on relating periodogram structure to the type of stochastic process which could have generated a 3D observed pattern. The results show that the methods based on spectral analysis developed in this work are able to identify patterns of three typical three-dimensional point processes, and can be used, concurrently, with analyzes in the space domain for a better characterization of spatial point patterns.

Test for Detection of Weak Graphic Passwords in Passpoint Based on the Mean Distance between Points

“…Said graphical passwords can be interpreted as a point spatial pattern [9][10][11][12][13][14][15] of five points studied by the various techniques of the theory of spatial randomness to determine their behavior. Precisely, two of the tests mostly used in this area to verify spatial randomness are the Ripley's K function test [9,11,13,[16][17][18][19][20][21][22], and the test of the distance to the nearest neighbor [9][10][11]17], which were tested in [23] to measure their effectiveness in detecting clustered graphical passwords in the Passpoint scenario.…”