Yasushi Yamaguchi

A nonmanifold topology model can surmount the limitations of traditional solid models. We propose a data structure and two classes of operations, focusing on neighborhood relationships and boundary information. The domain of our study is cell decomposition in a 3D Euclidean space. The study concentrated on representing and manipulating ordering information with compact representation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Extended visual cryptography [Ateniese et al., Theor. Comput. Sci. 250, 143–161 (2001)] is a method that encodes a number of images so that when the images are superimposed, a hidden image appears while the original images disappear. The decryption is done directly by human eyes without cryptographic calculations. Our proposed system takes three natural images as input and generates two images that are modifications of two of the input pictures. The third picture is viewed by superimposing the t

Visualization of distributed processes is useful for the management of large-scale distributed computing systems. Reactivity and scalability are especially important requirements for such visualization of distributed processes. We have proposed the visualization technique "Data Jewelry Box" algorithm, which satisfies both of the above requirements. The technique can be applied for the visualization of distributed processes, however, the algorithm has a problem that may yield much different data

User friendliness is one of the unresolved problems in CAD systems. There are many possible directions for improving user friendliness. Understanding of the modeling process is one of the most important directions. It is natural for a user to describe the model in terms of its evolution. We call this concept model derivation. To construct and use model derivation, we propose a history mechanism which keeps and manipulates the history of the modeling process. The history mechanism manages high le

One of the essential properties of a surface is its normal vector. Many applications, i.e., surface rendering, surface-surface intersection, and offset surface generation, require normal vectors. A normal vector at a point on a tensor product surface is usually obtained by taking a cross product of the two partial derivatives. The paper discusses a Bezier normal vector surface which is a locus of an unnormalized cross product normal vector. It also explains several applications of the Bezier nor

Visual cryptography is a kind of cryptography that can be decrypted only by a human visual system when stacking transparencies. Extended visual cryptography allows to print meaningful images on transparencies which can conceal the existence of 'secret' in the transparencies. Many studies have tried to incorporate continuous–tone images into extended visual cryptography. However, most of them failed in preserving the image quality after the encryption. This paper introduces a scheme for extended

Differential properties, e.g., a normal vector, are important characteristics of a surface. Most of the applications such as surface rendering, surface-surface intersection, and surface fairing, require the differential properties. These properties are well defined in differential geometry which has some assumptions in order to guarantee the calculation of differential properties. For instance, a normal vector of a parametric surface can be calculated as a cross product of two partial derivative

Surface-surface intersection is one of essential techniques in geometric modeling. A relatively robust algorithm to calculate intersections of parametric surfaces is a marching method which repeatedly calculates consecutive points on an intersection curve starting with a certain point. However, it is difficult to find starting points of all branches of intersections especially when the branches form small loops. It is also difficult to trace a curve near singular points. Critical points which ha