Hanqiu Sun

Parallel-split shadow maps for large-scale virtual environments

Shadowing effects dramatically enhance the realism of virtual environments by providing useful visual cues. Shadow mapping is an efficient algorithm for real-time shadow rendering, which is extensively adopted in real-time applications by its generality and efficiency. However, shadow mapping usually suffers from the inherent aliasing errors due to the image-based nature. In this paper, we present the Parallel-Split Shadow Maps (PSSMs) scheme, which splits the view frustum into different parts by using the planes parallel to the view plane and then generates multiple smaller shadow maps for the split parts. A fast and robust split strategy based on the analysis of shadow map aliasing has been proposed, which produces a moderate aliasing distribution over the whole depth range. By applying the geometry approximation procedure to each of the split parts instead of the whole scene, the tighter bounding shapes of visible objects enhance the utilization of the shadow map resolution. Hardware-acceleration is used to remove the extra rendering passes when synthesizing the scene-shadows. Our approach is intuitive to implement without using complex data structures, with real-time performance for dynamic and large-scale virtual environments.

RECODE: an image‐based collision detection algorithm

Object interactions are ubiquitous in interactive computer graphics, 3D object motion simulations, virtual reality and robotics applications. Most collision detection algorithms are based on geometrical object-space interference tests. Some algorithms have employed an image-space approach to the collision detection problem. In this paper we demonstrate an image-space collision detection process that allows substantial computational savings during the image-space interference test. This approach makes efficient use of the graphics rendering hardware for real-time complex object interactions. Copyright

Interactive deformation of soft tissues with haptic feedback for medical learning

An effective deformable model based on a successive force propagation process is proposed. It avoids the laborious stiffness matrix formulation and is scalable simply by controlling the penetration depth. Mechanical tests are performed to evaluate its feasibility for modeling real tissues. An interactive system is developed using a commercial haptic device.

Real-time haptic sculpting in virtual volume space

Virtual sculpture is a modeling technique for computer graphics based on the notion of sculpting a solid material with tools. Currently, most interactive sculpture is mainly focused on vision-based sensory channel. With visual feedback alone virtual sculpture cannot simulate the realistic sculpting operations in the physical world. The sense of touch, in combination with our kinesthetic sense, is capable of adding a new modality to virtual sculpture, especially in presenting complex geometry & material properties. In this paper, we propose a virtual haptic sculpting (VHS) system in the volume space, which supports real-time melting, burning, stamping, painting, constructing and peeling interactions. Based on the constructive volume methodology, we have developed sculpting tools as volumes, with each properties and size, distribution for elements, and rules of the interaction between the volumetric data and the tools. The sculpting tools are controlled directly by the 6-DOF haptic input to simulate realistic sculpting operations, in applying the computed model and tool dynamics while interacting with the volume. Both synthetic volumetric data and medical scan volumes are experimented using the 6-DOF PHANToM Desktop haptic interface.

Compact Video Synopsis via Global Spatiotemporal Optimization

Video synopsis aims at providing condensed representations of video data sets that can be easily captured from digital cameras nowadays, especially for daily surveillance videos. Previous work in video synopsis usually moves active objects along the time axis, which inevitably causes collisions among the moving objects if compressed much. In this paper, we propose a novel approach for compact video synopsis using a unified spatiotemporal optimization. Our approach globally shifts moving objects in both spatial and temporal domains, which shifting objects temporally to reduce the length of the video and shifting colliding objects spatially to avoid visible collision artifacts. Furthermore, using a multilevel patch relocation (MPR) method, the moving space of the original video is expanded into a compact background based on environmental content to fit with the shifted objects. The shifted objects are finally composited with the expanded moving space to obtain the high-quality video synopsis, which is more condensed while remaining free of collision artifacts. Our experimental results have shown that the compact video synopsis we produced can be browsed quickly, preserves relative spatiotemporal relationships, and avoids motion collisions.Video synopsis aims at providing condensed representations of video data sets that can be easily captured from digital cameras nowadays, especially for daily surveillance videos. Previous work in video synopsis usually moves active objects along the time axis, which inevitably causes collisions among the moving objects if compressed much. In this paper, we propose a novel approach for compact video synopsis using a unified spatiotemporal optimization. Our approach globally shifts moving objects in both spatial and temporal domains, which shifting objects temporally to reduce the length of the video and shifting colliding objects spatially to avoid visible collision artifacts. Furthermore, using a multilevel patch relocation (MPR) method, the moving space of the original video is expanded into a compact background based on environmental content to fit with the shifted objects. The shifted objects are finally composited with the expanded moving space to obtain the high-quality video synopsis, which is more condensed while remaining free of collision artifacts. Our experimental results have shown that the compact video synopsis we produced can be browsed quickly, preserves relative spatiotemporal relationships, and avoids motion collisions.

√3-Subdivision-Based Biorthogonal Wavelets

A new efficient biorthogonal wavelet analysis based on the radic3 subdivision is proposed in the paper by using the lifting scheme. Since the radic3 subdivision is of the slowest topological refinement among the traditional triangular subdivisions, the multiresolution analysis based on the radic3 subdivision is more balanced than the existing wavelet analyses on triangular meshes and accordingly offers more levels of detail for processing polygonal models. In order to optimize the multiresolution analysis, the new wavelets, no matter whether they are interior or on boundaries, are orthogonalized with the local scaling functions based on a discrete inner product with subdivision masks. Because the wavelet analysis and synthesis algorithms are actually composed of a series of local lifting operations, they can be performed in linear time. The experiments demonstrate the efficiency and stability of the wavelet analysis for both closed and open triangular meshes with radic3 subdivision connectivity. The radic3-subdivision-based biorthogonal wavelets can be used in many applications such as progressive transmission, shape approximation, and multiresolution editing and rendering of 3D geometric models.

Unlifted loop subdivision wavelets

In this paper, we propose a new wavelet scheme for loop subdivision surfaces. The main idea enabling our wavelet construction is to extend the subdivision rules to be invertible, thus executing each inverse subdivision step in the reverse order makes up the wavelet decomposition rule. As opposed to other existing wavelet schemes for loop surfaces, which require solving a global sparse linear system in the wavelet analysis process, our wavelet scheme provides efficient (linear time and fully in-place) computations for both forward and backward wavelet transforms. This characteristic makes our wavelet scheme extremely suitable for applications in which the speed for wavelet decomposition is critical. We also describe our strategies for optimizing free parameters in the extended subdivision steps, which are important to the performance of the final wavelet transform. Our method has been proven to be effective, as demonstrated by a number of examples.

RECODE: an image-based collision detection algorithm

Object interactions are ubiquitous in interactive computer graphics, 3D object motion simulations, virtual reality and robotics applications. Most collision detection algorithms are based on geometrical object space interference tests. Some algorithms have employed an image space approach to the collision detection problem. We demonstrate an image space collision detection process that allows substantial computational savings during the image space interference test. This approach makes efficient use of the graphics rendering hardware for real time complex object interactions.

Dynamic labeling management in virtual and augmented environments

Most applications in virtual and augmented reality usually need to visualize large amounts of extra text/image/video annotations associated with objects to assist users navigation. Labeling is one of the most intuitive techniques to achieve this goal, which attaches specific texts to related objects to provide users a clear environmental clue. The basic problem of labeling is the clutters due to unexpected overlapping and occlusion among labels and objects, which makes the environment ambiguous and obscure. In this paper, we present the interactive system of dynamic labeling management to address this problem for virtual environment navigation applications. Our system integrates the techniques of labeling with adaptive placement, view-driven label filtering and structured label searching. These features have been developed in our system with well display of augmented labels in VR applications.

Deformable simulation using force propagation model with finite element optimization

Abstract A key challenge of deformable simulation is to satisfy the conflicting requirements of real-time interactivity and physical realism. In this paper, we present the mass–spring-based force propagation model (FPM) in which the simulation speed is tunable to maintain a balance between the two criteria. Deformation is modeled as a result of force propagation among the mass points in localized regions. Experiments have been performed to study the effects of the FPM parameters on the eventual deformation. Furthermore, a heuristic optimization technique is proposed to identify the model parameters for materials as specified by mechanical constants. We employ simulated annealing to tune the parameters automatically until the simulated shape of the FPM approximates the reference deformation as defined by the mathematically more rigorous finite element model. The proposed technique provides a feasible solution to the issue of parameter identification in mass–spring-based models.