Yasuhiro Akagi

Computer animation of swaying trees based on physical simulation

Abstract This paper presents a series of techniques for generating animations of trees swaying in the wind, in consideration of the influences that the tree shapes and leaf sizes give to the air current. To do the simulation of the wind around a tree having a complicated shape, it is necessary to consider the influence that some objects obstructing the wind such as leaves or branches give. Generally, the following problem occurs when we use the incompressible Navier–Stokes equations in a physical simulation model of the wind. Computational complexity increases because of considering the details of tree shapes, so it is difficult to generate the animations in real-time. Therefore, this paper proposes a novel method that reduces the computational complexity and realizes an animation in real-time, by means of a boundary condition map expressing space distribution of resistances from tree models automatically. In this case, we treat the parts that have similar shapes such as leaves and branches as simple damping factors decreasing the wind velocity. And also, it has another advantage that the influences between a tree and others can be rapidly calculated by using a hierarchical calculation method. Finally, through many experiments using these methods, it is shown that real-time animations of swaying trees in the wind can be realized.

Stochastic driver speed control behavior modeling in urban intersections using risk potential-based motion planning framework

In unsignalized intersections with poor visibility, proactive driving with hazard anticipation is required in order to avoid collisions with other traffic participants from a blind corner. However, for elderly drivers and novice drivers, it is difficult to recognize potential hazardous area and difficult to select an appropriate speed to pass the intersections safely. To assist such drivers, a driver model which can recommend the appropriate speed by learning driving data of expert drivers based on a statistical approach is useful for a driver assistance system. The proposed method automatically estimates parameters of the driver model from the actual driving data by defining risk potential functions for representing braking behaviors while passing through intersections, oncoming vehicles and pedestrians. To evaluate the proposed method, the driving data of instructors of a driving school are collected. The results show that the accuracy (RMSE) of the estimated braking behavior model is 2.5 km/h against the actual data.

Interactive 3D animation system based on touch interface and efficient creation tools

Recently importance of tablet devices with touch interface increases significantly, because they attract not only mobile phone users, but also people of all generations including small kids to elderly people. One key technology on those devices is 3D graphics; some of them exceed the ability of desktop PCs. Although currently 3D graphics are only used for game applications, it also has a great potential for other purposes. For example, an interactive 3D animation system for tablet devices has been developed recently and attracts many people. With the system, multiple 3D animations are played depending on view direction and users gesture input. However, the system still has two critical issues: the first one is a complicated process for data creation, and the other is a conflict on several gestures overlapped at the same position. In the paper, the first issue is solved by using a realtime range sensor and the second one is solved by considering the relationship between the 3D object and the input 2D gesture. The effectiveness of the system was proved by making the real system and creating and manipulating the actual 3D animations.

Longitudinal and lateral motion planning method for avoidance of multi-obstacles in urban environments based on inverse collision probability

This paper presents a longitudinal and lateral motion planning method for driver assistance systems in urban scenarios. We proposed a Bayesian network based motion planner to generate the trajectory, including the positions and velocities to path through multiple traffic participants. To design the probabilistic models which represent a lane keeping maneuver and an obstacle avoidance maneuver, we collect and analyze natural driving data. Then, it is difficult to collect collision data in the real world. Therefore, we analyze the inverse collision probability from safety driving trajectories of expert drivers. The proposed method generates the optimal trajectory plan by using the global optimization algorithm named Belief Propagation. Finally, we show the evaluation experiment that compares the difference between the trajectories generated by the proposed method and natural driving data.

An analysis of an elderly driver behaviour in urban intersections based on a risk potential model

This paper proposes a driving safety evaluation method based on the parameter analysis of a driver model. Since the driving abilities, such as reaction, recognition and judgment time decrease with aging, it is difficult for elderly drivers to avoid the traffic accidents instantly. Therefore, the proactive safety driving is important for the elderly drivers to prevent the accidents. Then, the safety evaluation criteria of a driving behavior are useful to encourage the driver to keep proactive safety driving. And these criteria are useful to develop an advanced driver assistance system for elderly drivers. To evaluate the driving behavior, we use the parameters of a risk potential model which is the driver model to represent the speed and course control around the risk factors. Since the risk potential model represents the driving behavior by using a small number of the parameters, we make the assumption that the parameters are highly abstract the driving behavior and it is useful for analyzing the safety level of the driver. To evaluate the assumption experimentally, we collect the actual driving data of elderly, general and normative drivers for analyzing the parameters of the risk potential model and the safety level of the driver. Finally, the results show that the parameters of the risk potential model can be used to indicate the features of the driving behavior of the elderly drivers.

Interactive 3D Animation Creation and Viewing System based on Motion Graph and Pose Estimation Method

This paper proposes an interactive 3D animation system specifically aiming efficient control of human motion. However there are various commercial products for creating movies and game contents, those are still difficult to deal with for non-professional users. To ease the creation process and encourage to utilize 3D animation for the general users, e.g., in the field of such as education, medicine and so on, we propose a system using Kinect. The data of skeleton models of human motion estimated by Kinect is processed to generate Motion Graph and finally restructure the data automatically for 3D character models. We also propose an efficient 3D animation viewing system based on touch interface for tablet device, which enables intuitive control of multiple motions of the human activity. To evaluate the effectiveness of the method, we implemented a prototype system and created several 3D animations.

Exemplar-Based Hole-Filling Technique for Multiple Dynamic Objects

Entire shape reconstruction of dynamic objects is an important research subject with applications on film production, virtual reality, modeling and engineering. Typically, entire shape reconstruction of real objects is achieved by combining the outcome of objects scanned from multiple directions. However, due to limitations on the number of 3D sensors enclosing the scene, occlusions inevitably occur, causing holes to appear on the reconstructed surfaces. These issues are intensified if dynamic, moving objects are considered. Volumetric and polygonal approaches exist to address these problems. Most notably, exemplar-based polygonal methods have gained momentum due to their overall improved visual quality. In this paper we propose an extension to the plain exemplar-based technique that allows for multiple dynamic objects. With our method, adequate hole-filling candidates are sampled from spatial and temporal domains and then used to synthesize likely plausible surfaces with smooth boundaries for the hole regions.

A facial tracking and transfer method with a key point refinement

We propose a key point detection and refinement method for a facial motion tracking and transfer. Since key-point-based approaches for representing facial expressions usually deform faces by interpolating movements of the key points, the approaches cause errors between the deformed face and the original one. To solve this problem, our method tracks non-rigid deformations of surfaces to detects additional key points for minimizing the errors.

Controlling color regions of leaves with painting techniques for landscape arts

In this paper, we propose a non-photorealistic rendering (NPR) framework for creating landscape art in traditional animation. The proposed method is based on painting techniques for landscape arts, which enables a user to reproduce features of the target work of art and its style. Landscape (background) arts is generally used in animation productions. One image of landscape art and multiple layers of moving characters compose a scene. Landscape art is one of most important factors for making the impression of an animation. We propose a NPR technique that reproduces painting techniques for landscape arts such as leaf painting based on just a few colors, shading to produce a spherical effect. The technique developed by the authors generates dynamic landscape art having a swaying motion in the wind by applying the animation generation technique for swaying trees to it.