Min-Hyung Choi

Fast Volume Preservation for a Mass-Spring System

This article presents a new method to model fast volume preservation of a mass-spring system to achieve a realistic and efficient deformable object animation, without using internal volumetric meshing. With this method the simulated behavior is comparable to a finite-element-method-based model at a fraction of the computational cost

Effective Constrained Dynamic Simulation Using Implicit Constraint Enforcement

Stable and effective enforcement of hard constraints is one of the crucial components in controlling physics-based dynamic simulation systems. The conventional explicit Baumgarte constraint stabilization confines the time step to be within a stability limit and requires users to pick problem-dependent coefficients to achieve fast convergence or to prevent oscillations. The recently proposed post-stabilization method has shown a successful constraint drift reduction but it does not guarantee the physically correct behavior of motion and requires additional computational cost to decrease the constraint errors. This paper presents our new implicit constraint enforcement technique that is stable over large time steps and does not require problem dependent stabilization parameters. This new implicit constraint enforcement method uses the future time step to estimate the correct magnitude of the constraint forces, resulting in better stability over bigger time steps. More importantly, the proposed method generates physically conforming constraint forces while minimizing the constraint drifts, resulting in physically correct motion. Its asymptotic computational complexity is same as the explicit Baumgarte method. It can be easily integrated into various constrained dynamic systems including rigid body or deformable structure applications. This paper describes a formulation of implicit constraint enforcement and an accumulated constraint error and dynamic behavior analysis for comparison with existing methods.

Virtual reality prototype for measurement of expression characteristics in emotional situations

Expressions are a basic necessity for daily living, as they are required for managing relationships with other people. Conventional expression training has difficulty achieving an objective measurement, because their assessment depends on the therapists ability to assess a patients state or training effectiveness. In addition, it is difficult to provide emotional and social situations in the same manner for each training or assessment session. Virtual reality techniques can overcome shortcomings occurring in conventional studies by providing exact and objective measurements and emotional and social situations. In this study, we developed a virtual reality prototype that could present emotional situation and measure expression characteristics. Although this is a preliminary study, it could be considered that this study shows the potential of virtual reality as an assessment tool.

Interactive Motion Control of Deformable Objects Using Localized Optimal Control

In this paper we present a novel interactive method and interface techniques for controlling the behavior of physically-based simulation of deformable objects. The goal of our research is to provide users an ability to control the motion which appears physically correct, preserves the moving pattern of the original motion, and satisfies goals for a deformable object. In our approach, a user can select any part of the deformable structure, called control points, and can define target poses by moving control points. A user also can define target poses then our system automatically generates the motion path to achieve the target pose. With this technique patient specific organ simulation can be achieved by using a stream of image data. A series of sectional images can be the target poses. The optimal path generator computes the required control parameters that steer the intended node to the desired goal position while preserving the moving pattern of the original motion. It guarantees that the edited motion is physically conforming and natural.

User interface guidelines for enhancing usability of airline travel agency e-commerce web sites

Specific user interface guidelines are described to increase the usability of airline travel e-commerce Web sites. Although previous guidelines address the usability issue from the perspective of the sale of tangible products that can be described and depicted, less attention has been given to the usability issues for the sale of services. Service industries have different requirements for communicating with customers, specifically regarding their product offerings. This is prominent in the air travel industy, where Web site usability is known to be poor. We examine how the current guidelines are inadequate for Web sites providing air travel information. We propose specific guidelines for those sites that will enhance their usability.

An Improved ICP Algorithm Based on the Sensor Projection for Automatic 3D Registration

Three-dimensional (3D) registration is the process aligning the range data sets form different views in a common coordinate system. In order to generate a complete 3D model, we need to refine the data sets after coarse registration. One of the most popular refinery techniques is the iterative closest point (ICP) algorithm, which starts with pre-estimated overlapping regions. This paper presents an improved ICP algorithm that can automatically register multiple 3D data sets from unknown viewpoints. The sensor projection that represents the mapping of the 3D data into its associated range image and a cross projection are used to determine the overlapping region of two range data sets. By combining ICP algorithm with the sensor projection, we can make an automatic registration of multiple 3D sets without pre-procedures that are prone to errors and any mechanical positioning device or manual assistance. The experimental results demonstrated that the proposed method can achieve more precise 3D registration of a couple of 3D data sets than previous methods.

An adaptive collision detection and resolution for deformable objects using spherical implicit surface

A fast collision detection and resolution scheme is one of the key components for interactive simulation of deformable objects. It is particularly challenging to reduce the computational cost in collision detection and to achieve the robust treatment at the same time. Since the shape and topology of a deformable object changes continuously unlike the rigid body, an efficient and effective collision detection and resolution is a major challenge. We present a fast and robust collision detection and resolution scheme for deformable objects using a new enhanced spherical implicit surface hierarchy. The penetration depth and separating distance criteria can be adjusted depending on the application specific error tolerance. Our comparative experiments show that the proposed method performs substantially faster than existing algorithms for deformable object simulation with massive element-level collisions at each iteration step. Our adaptive hierarchical approach enables us to achieve a real-time simulation rate, well suited for interactive applications.

Adaptive surface-deformable model with shape-preserving spring

This paper presents a multi‐resolutional surface deformable model with physical property adjustment scheme and shape‐preserving springs to represent surface‐deformable objects efficiently and robustly. In order to reduce the computational complexity while ensuring the same global volumetric behaviour for the deformable object, we introduce a multi‐resolutional mass‐spring model that is locally refined using the modified‐butterfly subdivision scheme. For robust deformation, a shape‐preserving spring, which helps to restore the model to the original shape, is proposed to reduce the animation instability. Volume and shape preservation is indirectly achieved by restoring the model to the original shape without computing the actual volume and associated forces at every iteration. Most existing methods concentrate on visual realism of multi‐resolutional deformation and often neglect to maintain the dynamic behavioural integrity between detail levels. In order to preserve overall physical behaviour, we present a new scheme for adjusting physical properties between different levels of details. During the animation of deformable objects, the part of the object under external forces beyond a threshold or with large surface curvature variations is refined with a higher level of detail. The physical properties of nodes and springs in the locally refined area are adjusted in order to preserve the total mass and global behaviour of the object. The adequacy of the proposed scheme was analysed with tests using practical mesh examples. Experimental results demonstrate improved efficiency in object deformation and preservation of overall behaviour between different levels. Copyright

Two quantitative measures of inlier distributions for precise fundamental matrix estimation

Because the estimation of a fundamental matrix is much dependent on the correspondence, it is important to select a proper inlier set that represents variation of the image due to camera motion. Previous studies showed that a more precise fundamental matrix can be obtained if the evenly distributed points are selected. When the inliers are detected, however, no previous methods have taken into account their distribution. This paper presents two novel approaches to estimate the fundamental matrix by considering the inlier distribution. The proposed algorithms divide an entire image into several sub-regions, and then examine the number of the inliers in each sub-region and the area of each region. In our method, the standard deviations are used as quantitative measures to select a proper inlier set. The simulation results on synthetic and real images show that our consideration of the inlier distribution can achieve a more precise estimation of the fundamental matrix.

Real-Time Tidal Volume Estimation Using Iso-surface Reconstruction

Breathing volume measurement has long been an important physiological indication widely used for the diagnosis and treatment of pulmonary diseases. However, most of existing breathing volume monitoring techniques require either physical contact with the patient or are prohibitively expensive. In this paper we present an automated and inexpensive non-contact, vision-based method for monitoring an individuals tidal volume, which is extracted from a three-dimensional (3D) chest surface reconstruction from a single depth camera. In particular, formulating the respiration monitoring process as a 3D space-time volumetric representation, we introduce a real-time surface reconstruction algorithm to generate omni-direction deformation states of a patients chest while breathing, which reflects the change in tidal volume over time. These deformation states are then used to estimate breathing volume through a per-patient correlation metric acquired through a Bayesian-network learning process. Through prototyping and implementation, our results indicate that we have achieved 92.2% to 94.19% accuracy in the tidal volume estimations through the experimentation based on the proposed vision-based method.