Jyh-Ming Lien

Simultaneous shape decomposition and skeletonization

Shape decomposition and skeletonization share many common properties and applications. However, they are generally treated as independent computations. In this paper, we propose an iterative approach that simultaneously generates a hierarchical shape decomposition and a corresponding set of multi-resolution skeletons. In our method, a skeleton of a model is extracted from the components of its decomposition --- that is, both processes and the qualities of their results are interdependent. In particular, if the quality of the extracted skeleton does not meet some user specified criteria, then the model is decomposed into finer components and a new skeleton is extracted from these components. The process of simultaneous shape decomposition and skeletonization iterates until the quality of the skeleton becomes satisfactory. We provide evidence that the proposed framework is efficient and robust under perturbation and. deformation. We also demonstrate that our results can readily be used in problems including skeletal deformations and virtual reality navigation.

An obstacle-based rapidly-exploring random tree

Tree-based path planners have been shown to be well suited to solve various high dimensional motion planning problems. Here we present a variant of the Rapidly-Exploring Random Tree (RRT) path planning algorithm that is able to explore narrow passages or difficult areas more effectively. We show that both workspace obstacle information and C-space information can be used when deciding which direction to grow. The method includes many ways to grow the tree, some taking into account the obstacles in the environment. This planner works best in difficult areas when planning for free flying rigid or articulated robots. Indeed, whereas the standard RRT can face difficulties planning in a narrow passage, the tree based planner presented here works best in these areas

Shepherding Behaviors with Multiple Shepherds

Shepherding behaviors are a type of group be haviors in which one group (the shepherds) tries to control the motion of another group (the flock). Shepherding behaviors can be found in many forms in nature and have various important robotic applications. In this paper we extend our previous work of shepherding behaviors with a single shepherd to multiple shepherds. More specifically, we study how a group of shepherds can work cooperatively without communication to efficiently control the flock.

A general framework for sampling on the medial axis of the free space

We propose a general framework for sampling the configuration space in which randomly generated configurations, free or not, are retracted onto the medial axis of the free space. Generalizing our previous work, this framework provides a template encompassing all possible retraction approaches. It also removes the requirement of exactly computing distance metrics thereby enabling application to more realistic high dimensional problems. In particular, our framework supports methods that retract a given configuration exactly or approximately onto the medial axis. As in our previous work, exact methods provide fast and accurate retraction in low (2 or 3) dimensional space. We also propose new approximate methods that can be applied to high dimensional problems, such as many DOF articulated robots. Theoretical and experimental results show improved performance on problems requiring traversal of narrow passages. We also study tradeoffs between accuracy and efficiency for different levels of approximation, and how the level of approximation effects the quality of the resulting roadmap.

Roadmap-based flocking for complex environments

Flocking behavior is very common in nature, and there have been ongoing research efforts to simulate such behavior in computer animations and robotics applications. Generally, such work considers behaviors that can be determined independently by each flock member solely by observing its local environment, e.g., the speed and direction of its neighboring flock members. Since flock members are not assumed to have global information about the environment, only very simple navigation and planning techniques have been considered for such flocks. In this paper, we investigate how the addition of global information in the form of a roadmap of the environment enables more sophisticated flocking behaviors. In particular, we study and propose new techniques for three distinct group behaviors: homing, exploring and shepherding. These behaviors exploit global knowledge of the environment and utilize knowledge gathered by all flock members. This knowledge is communicated by allowing individual flock members to dynamically update the shared roadmap to reflect (un)desirable routes or regions. We present experimental results showing how the judicious use of simple roadmaps of the environment enables more complex behaviors to be obtained at minimal cost.

Planning motion in completely deformable environments

Though motion planning has been studied extensively for rigid and articulated robots, motion planning for deformable objects is an area that has received far less attention. In this paper we present a framework for planning paths in completely deformable, elastic environments. We apply a deformable model to the robot and obstacles in the environment and present a kinodynamic planning algorithm suited for this type of deformable motion planning. The planning algorithm is based on the rapidly-exploring random tree (RRT) path planning algorithm. To the best of our knowledge, this is the first work that plans paths in totally deformable environments

Automatically generating virtual guided tours

After the introduction of VRML, 3D Web browsing has become a popular form of networked virtual reality. However, it is still a great challenge for a novice user equipped with a regular desktop PC to navigate in most virtual worlds of moderate complexity. We think the main problem is due to the fact that a user usually uses a 2D mouse to provide low-level navigation control but the display frame rate is not high enough for this servo loop. We consider an alternative metaphor of allowing a user to specify locations of interests on a 2D-layout map and let the system automatically generate the animation of guided tours in virtual architectural environments. Specifically, we aim to generate animations of customizable tour paths and its associated human/camera motions in an on-line manner according to high-level user inputs. We describe an auto-navigation system, in which several efficient path-planning algorithms adapted from robotics are used. This system has been implemented in Java and adopts common VRML browsers as its 3D interface. We also use the geometric model of our departmental building as an example to demonstrate the efficiency and effectiveness of the system.

Point-Based Minkowski Sum Boundary

Minkowski sum is a fundamental operation in many geometric applications, including robotics, penetration depth estimation, solid modeling, and virtual prototyping. However, due to its high computational complexity and several nontrivial implementation issues, computing the exact boundary of the Minkowski sum of two arbitrary polyhedra is generally a difficult task. In this work, we propose to represent the boundary of the Minkowski sum approximately using only points. Our results show that this point-based representation can be generated efficiently. An important feature of our method is its straightforward implementation and parallelization. We also demonstrate that the point-based representation of the Minkowski sum boundary can indeed provide similar functionality as mesh-based representations can. We show several applications in motion planning, penetration depth approximation and modeling.Radiometric compensation techniques allow seamless projections onto complex everyday surfaces. Implemented with projector-camera systems they support the presentation of visual content in situations where projection-optimized screens are not available or not desired - as in museums, historic sites, air-plane cabins, or stage performances. We propose a novel approach that employs the full light transport between projectors and a camera to account for many illumination aspects, such as interreflections, refractions, shadows, and defocus. Precomputing the inverse light transport in combination with an efficient implementation on the GPU makes the real-time compensation of captured local and global light modulations possible.

Approximate convex decomposition

Decomposition is a technique commonly used to break complex models into sub-models that are easier to handle. Convex decomposition, which partitions the model into convex components, is interesting because many algorithms perform more efficiently on convex objects than on non-convex objects. One issue with convex decompositions, however, is that they can be costly to construct and can result in representations with an unmanageable number of components. In many applications, the detailed features of the model are not crucial and in fact considering them only serves to obscure important structural features and adds to the processing cost. In such cases, an approximate representation of the model that captures the key structural features would be preferable.

Covering Minkowski sum boundary using points with applications

Minkowski sum is a fundamental operation in many geometric applications, including robotic motion planning, penetration depth estimation, solid modeling, and virtual prototyping. However, due to its high computational complexity and several non-trivial implementation issues, computing the exact boundary of the Minkowski sum of two arbitrary polyhedra is generally a difficult task. In this work, we propose to represent the boundary of the Minkowski sum approximately using only points. Our results show that this point-based representation can be generated efficiently. An important feature of our method is its straightforward implementation and parallelization. We demonstrate that the point-based representation of the Minkowski sum boundary can indeed provide similar functionality as the mesh-based representations can. We show several applications in motion planning, penetration depth approximation and geometric modeling. An implementation of the proposed method can be obtained from our project webpage.