Sensation-preserving haptic rendering

Most human-computer interactive systems focus primarily on the graphical rendering of visual information and, to a lesser extent, on the display of auditory information. Haptic interfaces have the potential to increase the quality of human-computer interaction by accommodating the sense of touch. They provide an attractive augmentation to visual display and enhance the level of understanding of complex data sets. A haptic rendering system generates contact or restoring forces to prevent penetration into the virtual objects and create a sense of touch. The system computes contact forces by first detecting if a collision or penetration has occurred. Then, the system determines the (projected) contact points on the model surface. Finally, it computes restoring forces based on the amount of penetration. Researchers have recently investigated the problem of rendering the contact forces and torques between 3D virtual objects. This problem is known as six-degrees-of-freedom (6-DOF) haptic rendering, as the computed output includes both 3-DOF forces and 3-DOF torques. This article presents an overview of our work in this area. We suggest different approximation methods based on the principle of preserving the dominant perceptual factors in haptic exploration.     

Layered textures for image-based rendering

An extension to texture mapping is given in this paper for improving the efficiency of image-based rendering. For a depth image with an orthogonal displacement at each pixel, it is decomposed by the displacement into a series of layered textures (LTs) with each one having the same displacement for all its texels. Meanwhile, some texels of the layered textures are interpolated for obtaining a continuous 3D approximation of the model represented in the depth image. Thus, the plane-to-plane texture mapping can be used to map these layered textures to produce novel views and the advantages can be obtained as follows: accelerating the rendering speed, supporting the 3D surface details and view motion parallax, and avoiding the expensive task of hole-filling in the rendering stage. Experimental results show the new method can produce high-quality images and run faster than many famous image-based rendering techniques.     

Using analytical force model for efficient deformation simulation and haptic rendering of soft objects

Multimedia Tools and Applications - High refresh rate required for haptic rendering has been an issue in immersive virtual-reality based simulation. It prohibits the use of physically accurate yet...     

Synergistic visual/haptic rendering modes for scientific visualization

Our approach uses a visual/haptic interface to display scientific data both graphically and haptically. The haptic interface provides a natural means of interacting with the data through direct tactile sensing and manipulation of the data display. Our experience with this interface suggests that users understand the data more clearly when the haptic component acts as a synergistic companion to the visual display. That is, rather than replace the visual display of data or display disparate data haptically, the haptic component reinforces and clarifies visual information via compatible haptic data rendering.     

Function-based approach to mixed haptic effects rendering

Commonly, surface and solid haptic effects are defined in such a way that they hardly can be rendered together. We propose a method for defining mixed haptic effects including surface, solid, and force fields. These haptic effects can be applied to virtual scenes containing various objects, including polygon meshes, point clouds, impostors, and layered textures, voxel models as well as function-based shapes. Accordingly, we propose a way how to identify location of the haptic tool in such virtual scenes as well as consistently and seamlessly determine haptic effects when the haptic tool moves in the scenes with objects having different sizes, locations, and mutual penetrations. To provide for an efficient and flexible rendering of haptic effects, we propose to concurrently use explicit, implicit and parametric functions, and algorithmic procedures.     

Toward realistic haptic rendering of surface textures

New sophisticated haptic-rendering algorithms let users experience virtual objects through touch. We systematically investigate the unrealistic behavior of virtual haptic textures. The emerging science of haptic rendering consists of delivering properties of physical objects through the sense of touch. Owing to the recent development of sophisticated haptic-rendering algorithms, users can now experience virtual objects through touch in many exciting applications, including surgical simulations, virtual prototyping, and data perceptualization. Haptics holds great promise to enrich the sensory attributes of virtual objects that these systems can produce. One area that has received increasing attention in the haptics community is haptic texture rendering, the goal of which is to introduce micro-geometry-scale features on object surfaces. Haptic objects rendered without textures usually feel smooth, and sometimes slippery. Appropriate haptic textures superimposed on haptic objects enhance an object's realism.     

Physically accurate haptic rendering with dynamic effects

We focus on the realism/transparency aspect of haptic rendering. We introduce a novel approach that enables physically correct and accurate simulation of contact wrench W/sub c/ for general rigid objects in real time, taking into account not only friction and gravity but also dynamic effects. Our method for contact force and moment simulation builds on the real-time identification of geometrically valid contact states despite digital errors. Our approach applies to general rigid bodies including both polyhedral and nonpolyhedral objects. For nonpolyhedral, curved objects, we build our contact state representation and contact force/moment model directly on the smooth and accurate representation of the object surfaces. Our approach's key idea is to solve for the contact force and moment analytically based on not only the contact configuration, but also the real-time identification of the exact type of the corresponding contact state, the type of instantaneous motion of the held object prior to reaching the contact configuration.     

Measurement-based modeling of contact forces and textures for haptic rendering

Haptic texture represents the fine-grained attributes of an object's surface and is related to physical characteristics such as roughness and stiffness. We introduce an interactive and mobile scanning system for the acquisition and synthesis of haptic textures that consists of a visually tracked handheld touch probe. The most novel aspect of our work is an estimation method for the contact stiffness of an object based solely on the acceleration and forces measured during stroking of its surface with the handheld probe. We establish an experimental relationship between the estimated stiffness and the contact stiffness observed during compression. We also measure the height-displacement profile of an object's surface enabling us to generate haptic textures. We show an example of mapping the textures on to a coarse surface mesh obtained with an image-based technique, but the textures may also be combined with coarse surface meshes obtained by manual modeling.     

Edge-preserving texture filtering for real-time rendering

Texture filtering is essential in enhancing the visual quality of real-time rendering. Conventional schemes do not consider the characteristics of texture content, thus the sharpness of edges in texture images cannot be retained. This paper proposes a novel texture-filtering algorithm, which consists of edge-preserving interpolation and edge-preserving MIP-map prefiltering. The memory bandwidth requirement is kept the same as in conventional schemes by dynamically adjusting the interpolation kernel. Hardware implementation is also provided to show the real-time processing capability. Published online: 28 January 2003     

High performance haptic device for force rendering in textile exploration

The HAPTEX system aims to develop a new multi-sensory environment for the immersive exploration of textiles. HAPTEX is based on a multi-layer/multi-thread architecture that optimizes the computational speed and integrates three different types of sensory feedback: vision, tactile and haptic. Such kind of environment is suitable for demanding VR applications such as the online marketing of novel textiles or garments, however it requires the design of a high performance multi-point haptic interface. The present work focuses on the haptic device design and describes how demanding requirements can be met by integrating on a high performance device a force sensor to achieve closed loop control. The methodology for the dimensioning of a motion based explicit force control on the basis of the dynamic parameters will be discussed and the specific implementation for the HAPTEX system presented.     

交互式实时水面渲热

介绍了一种利用可编程图形硬件来实现水面实时渲染的方法。该渲染过程分为两个阶段,即水面建模和光照实现。通过当前图形硬件新提供的顶点纹理技术来对水面进行建模,并结合环境纹理映射技术和二维纹理映射技术实现了水面上的反射与折射等光照现象。实验证明,该方法大大提高了渲染速度,增强了水面渲染的交互性和实时性。     

Stable haptic rendering in interactive virtual control laboratory

Stable control of haptic interfaces is one of the most important challenges in haptic simulations, because any instability of a haptic interface can cause it to get far from the realistic sense. In this paper, the control strategies employed for a stable haptic rendering in an interactive virtual control laboratory are presented. In this interactive virtual laboratory, there are different scenarios to teach the control concepts, in which a haptic interface is used in the two cases of force control and position control. In this regard, two control strategies are employed to avoid instability. An energy-compensating controller is utilized to remove energy leakage. Besides, a fuzzy impedance control is used along with the energy-compensating controller for the position control scenarios. The results obtained indicate the proposed approaches practically guarantee the stability of the haptic interface for an educational application in practice.     

基于GPU的点模型实时绘制

近几年随着GPU的可编程能力的增强,很多基于点的绘制算法都可以移植到GPU上来实现,这样既可以让CPU有时间来处理其他事,又可以通过GPU提高算法的运行速度。由于目前的GPU不支持epsilon-z-buffering算法,大部分基于GPU的绘制算法都是通过Multi-pass绘制来达到较高的绘制质量。然而,这些算法需要在第一和第二个pass中光栅化大量的可能可见的面圆,并在第二个pass的像素shader中对这些可能可见的面圆进行大量的计算。本文提出了一种基于GPU的改进Multi-pass绘制算法,与前面的Multi-pass算法相比,我们的算法只需在第一个pass中对大量可能可见的面圆进行光栅化和深度测试后,便可求出所有可见面圆,即离视点最近的面圆。然后在第二个pass中只对这些可见面圆进行光栅化和逐像素计算,从而避免了大量不必要的计算。     

View-dependent pruning for real-time rendering of trees

The main problem in the real-time rendering of vegetation is the massive amount of primitives to be rendered. These primitives are needed to fully describe the geometry of the plants. However, some of them are not visible depending on the location of the viewer. This work focuses on this fact to interactively reduce the amount of geometry needed to represent the foliage through a view-dependent multiresolution scheme. Following a camera-dependent criterion, the less visible parts of the foliage are detected in real time, and rendered with a decreased level of detail for improving efficiency. This fact considerably reduces the extraction and the visualization time of the geometry that represents the foliage. The novelty of the presented method is that its design is oriented to being efficient on massively parallel architectures, such as the graphics processing unit. Moreover, we introduce a new management system for efficiently handling level of detail objects in order to improve performance for forest scenes.     

Adaptive real-time level-of-detail based rendering for polygonalmodels

We present an algorithm for performing adaptive real-time level-of-detail-based rendering for triangulated polygonal models. The simplifications are dependent on viewing direction, lighting, and visibility and are performed by taking advantage of image-space, object-space, and frame-to-frame coherences. In contrast to the traditional approaches of precomputing a fixed number of level-of-detail representations for a given object, our approach involves statically generating a continuous level-of-detail representation for the object. This representation is then used at run time to guide the selection of appropriate triangles for display. The list of displayed triangles is updated incrementally from one frame to the next. Our approach is more effective than the current level-of-detail-based rendering approaches for most scientific visualization applications, where there are a limited number of highly complex objects that stay relatively close to the viewer. Our approach is applicable for scalar (such as distance from the viewer) as well as vector (such as normal direction) attributes     

Procedural generation of materials for real-time rendering

Multimedia Tools and Applications - The use of Procedural Content Generation techniques in the production of Video Games has seen a large diffusion in these last years. Regarding the procedural...     

Simplified photon mapping for real-time caustics rendering

The objective of this paper is to adapt photon mapping for real-time simulation of caustics. High-performance algorithm adapted for the GPU and implemented on the basis of cross-platform OpenGL and OpenCL APIs is proposed. For effective rendering of caustics and generation of photon map OpenGL shaders are used. Voxel acceleration structure constructed directly on the GPU by means of OpenCL provides fast access to photon map. Performance estimation for different equipment is given.     

Clustering and merging for real-time forest rendering

Rendering of large-scale forest scenes is a challenging task,whose highly geometric complexity will put heavy burden on current graphics hardware.When navigating the scene,the overall visual result is generally considered as the core concern.A new method is proposed in this paper for large-scale forest rendering using clustering and merging strategies.Our method improves the rendering effect by clustering polygons according to the point information with relation to neighbours.A fast forest rendering system is developed accordingly.The relative techniques in the system can improve the visual quality on demand of different applications.     

一种视点相关的大规模地形快速实时生成算法

为了解决大规模地形实时漫游过程中,由于不同细节层次模型之间过渡而引起的图像跳变以及图像绘制帧率不高的问题,提出了自底向上的一次性整体构网,网格节点实时更新的建模策略。运用基于块和三角形面片的混合裁剪模式 ,结合简化的高度差投影计算方法,快速选取适合的地形节点 ;然后采用加点、删点、局部更新三种途径对 Delaunay地形三角网进行实时更新。同时在地形漫游过程中实现了对高度差投影限的自适应控制。仿真实验表明,该算法有效地避免了图像跳变现象,与同类算法相比 ,具有较高的图像绘制帧率,特别适合大规模地形的近距离     

Penalty-based haptic rendering technique on medicinal healthy dental detection

Multimedia Tools and Applications - We present a penalty-based haptic rendering analysis method for medicinal dentistry diagnose simulation. The method is based on the locally optimized generalized...