Ken-ichi Kobori

A topology-preserving polygonal simplification using vertex clustering

Product developers have used a lot of polygon data, approximated from 3D-CAD data, as a collaboration tool on the Internet. It is difficult to deal with this data for example with respect to transmission, computational cost, or rendering, so simplification algorithms are required for data compression. In general, a vertex-clustering algorithm in simplification algorithms is very fast, although it has the problem that topology information is not preserved and for some applications, such as 3D-CAD, it is important to preserve topology information. We define topology information in this paper as genus on the polyhedron and 2-manifold. In this paper, we propose a topology-preserving simplification method using a depth-first search tree on a vertex-clustering algorithm. Our method does not lose the advantage that vertex-clustering algorithms are fast yet it solves the problem of lost topology information. Experimental results show that this method is effective and is easily adapted to space division algorithms of other vertex-clustering algorithms

An “Origami” Support System by Using Finger Gesture Recognition

We propose “Origami” simulation system using finger gesture recognition. “Origami” is a traditional and popular game using a square sheet of paper in Japan. It is built up only by folding called “Ori” operation. Thus the rule of “Origami” is very simple. However, it is difficult for children to use complicated “Ori” and it is necessary to retry “Ori” operation again and again. On the other hand, the durability of paper is limited. Therefore by using virtual paper and finger gesture recognition, there is no limitation of durability and people who play “Origami” can retry “Ori” operation until they are satisfied. Our system projects “Origami” image on the grass table and tracks fingers by using LEAP motion that is one of depth sensors. In addition, our system recognizes “Ori” gestures with finger motions and folds “Origami”. Using our system, people can plays “Origami” with a feeling of folding a real paper.

A Method of Automatic Cage Generation for Shape Deformation by Using Elastic Models

Laplacian-based mesh processing technique is a kind of shape deformation in Computer Graphics modeling. It is hard to deform shapes which constructed by a lot of vertices in real time, because computational cost is high. A cages-based mesh deformation method is used in order to control the computational cost. A cage is a polyhedron which envelops an original dense model and is constructed by few meshes. The main advantages of using cages in shape deformations are controlling high speed computation. Currently, the coarse cage is constructed mainly by hand, and the construction usually takes several hours, even longer. Furthermore, when the shape of the model to be deformed is complex, it is very hard to construct its coarse cage by hand. Therefore it is important to develop a convenient method to generate the coarse cage enveloping a model. In this paper, we propose a method of automatic cage generation.

A method of melting snow animation using mathematical morphology

Recently, computer graphics has been often used to express natural phenomena. In this study, we propose a new technique for representing the appearance of snow melting by a heat source in virtual space. The conventional methods focus on heat calculations from the source. However, these approaches do not consider that water refreezes after melting. In order to express the snow melting phenomenon with a high degree of realism, we introduce the Mathematical Morphology method to reduce the processing cost, and to consider that water infiltrates into the snow and freezes again. In addition, some experimental results show that images generated by this method are more realistic than conventional ones. Our method achieves the effect that the snow melts on the side facing the heat source, and that the hollow part of the snow is again filled by refreezing.

Three-Dimensional Image Information Media. A Method of Model Simplification Using Spatial Partitioning.

We propose an algorithm for automatic simplification of models of 3D objects based on a simplification technique that applies vertex-clustering. The major advantages of the vertex-clustering technique are its low computational cost and high data reduction rate. Thus, the method is suitable for use in real-time rendering.This paper presents a clustering method for better preservation of important features in the shape. Its major contributions include : improved tight octree, described by Luebke, and high accuracy as a result of estimating vertices for the distance between the octants at each level.

Three-Dimensional Image Information Media. A Data Compression Method for 3-D Shapes with Network Spatial Partitioning Representation Model.

This paper describes a new data compression method for spatial partitioning representation which gives a higher data compression ratio than conventional methods. To obtain high data compression, we introduce the Network model, which performs fast geometric operations for spatial partitioning representation. The Network model represents a shape by using only voxels on the surfaces. These voxels connect with each other to make a network structure. The model compresses data simply for spatial partitioning representation and has a better compression ratio than the Octree model. Moreover, the proposed method can eliminate a large quantity of voxel from Network model. The resulting compression ratio is better than the three-dimensional runlength approach. Experimental results show that the method is effective for compressing data for spatial partitioning representation and achieves a high compression ratio.