Interactive visual exploration of unsteady 3D flows

In this paper we describe an interactive physically-based animation system for dense meshes. Our method extracts a coarse mesh from an original mesh to make a tetrahedral mesh for the reduction of computational costs. For computing reaction forces we precompute penetration depth values and gradients at mesh vertices by creating a distance eld. They are interpolated when collisions are detected and are used for the calculation of forces with a penalty method. Our method can handle dense meshes with physically-based animation and collision response at interactive frame rates.

Objective To explore the effect of laparoscopic transabdominal preperitoneal hernia repair (TAPP) with 3D mesh on the pain degree and postoperative recurrence of inguinal hernia. Methods Seventy patients with inguinal hernia who underwent surgery in the First Affiliated hospital of Xinjiang Medical University from September 2016 to December 2017 were divided into the 3D mesh group (n=35) and the ordinary mesh group (n=35) according to the different meshes used during surgery. All patients were treated with TAPP. Among them, the mesh used in the 3D group was Bard-3DMAX hernia mesh, while the mesh used in the ordinary mesh group was Covidien (Tyco) hernia mesh. The operation indexes, postoperative pain visual analog scale (VAS), complications and recurrence of the two groups were observed and compared. Results There were no significant differences in operation time, hospital stay and intraoperative bleeding between the two groups (P>0.05). The operation-related expenses and the time of getting out of bed after operation in the 3D group were less than those in the ordinary mesh group (P 0.05). The score of VAS in the 3D group was lower than that in the ordinary mesh group at 24 hours, 72 hours, 7 days and 15 days after operation (P 0.05). Conclusion TAPP is a safe and effective surgical method. The use of 3D mesh can simplify the operation, reduce the postoperative pain of patients, and has reliable curative effect. It is worthy of clinical application. Key words: 3D mesh; Transabdominal preperitoneal prosthesis; Hernia, inguinal; Surgical indexes; Postoperative pain

We present a physically-based fluid simulation with dynamic grid refinement on parallel SIMD graphics hardware. The irregular and dynamic structure of an adaptive grid requires sophisticated memory access patterns as well as a decomposition of the problem for parallel processing and the distribution of tasks to multiple threads. In this paper, we focus on the representation and management of the dynamic grid on the graphics device for an efficient parallelization of the advection step and the iterative solving of the Poisson equation. In order to achieve high performance, we utilize the hardware's capabilities like fast cache access and trilinear filtering. Furthermore, expensive data transfer between host and device is minimized to avoid a major bottleneck. We report results on the inherent overhead of the dynamic grid compared to an equivalent Cartesian grid. In addition, a visual simulation of smoke is presented with radiosity-based illumination and volume ray casting at interactive frame rates.

Parallel rendering of large polygonal models with transparency is challenging due to the need for alpha-correct blending and compositing, which is costly for very large models with high depth complexity and spatial overlap. In this paper we compare the performance of raster-based rendering methods on mesh models of neurons using two applications, one of which is specifically tailored to the neuroscience application domain, the other a general purpose visualization tool with domain specific additions. The first implements both sort-first and sort-last and uses a scene graph style traversal to cull objects, and dual depth peeling for order independent transparency, whilst the other uses a simpler brute force data-parallel approach with sort last composition. The advantages and trade offs of these approaches are discussed.We present the optimized algorithms needed to achieve interactive frame rates for a non-trivial, real-world parallel rendering scenario. We show that a generic data visualization application can provide competitive performance when optimizing its rendering pipeline, with some loss of capability over an optimized domain-specific application.

We introduce a novel approach to image-space ray tracing ideally suited for the photorealistic synthesis of fully dynamic environments at interactive frame rates. Our method, designed entirely on the rasterization pipeline, alters the acceleration data structure construction from a per-fragment to a per-primitive basis in order to simultaneously support three important, generally conflicting in prior art, objectives: fast construction times, analytic intersection tests and reduced memory requirements. In every frame, our algorithm operates in two stages: A compact representation of the scene geometry is built based on primitive linked-lists, followed by a traversal step that decouples the ray-primitive intersection tests from the illumination calculations; a process inspired by deferred rendering and the path integral formulation of light transport. Efficient empty space skipping is achieved by exploiting several culling optimizations both in xy- and z-space, such as pixel frustum clipping, depth subdivision and lossless buffer down-scaling. An extensive experimental study is finally offered showing that our method advances the area of image-based ray tracing under the constraints posed by arbitrarily complex and animated scenarios.

Curved Planar Reformation is a powerful visualization technique for the diagnosis of vascular diseases. It allows an accurate centerline-driven investigation of vessel lumen while providing valuable anatomical context. Extended methods like Multipath Curved Planar Reformation, Centerline Reformation or Curved Surface Reformation provide additional flexibility by condensing entire vascular systems into rotatable views. Unfortunately, all these methods produce depth discontinuities because they operate in a projective fashion. While large discontinuities provide valuable hints about distinct anatomical contexts, small discontinuities, which frequently arise, have distracting effects on the visualization result and do not contribute significant information. In this paper we present a bilateral filtering technique which allows to selectively remove depth discontinuities without affecting discontinuities that carry information. The presented approach significantly improves the quality of vessel reformations, can be applied at interactive frame rates and is orthogonal to existing methods.

Interactive image deformation is an important feature of modern image processing pipelines. It is often used to create caricatures and animation for input images, especially photos. State-of-the-art image deformation techniques are based on transforming vertices of a mesh, which is textured by the input image, using affine transformations such as translation, and scaling. However, the resulting visual quality of the output image depends on the geometric resolution of the mesh. Performing these transformations on the CPU often further inhibits performance and quality. This is especially problematic on mobile devices where the limited computational power reduces the maximum achievable quality. To overcome these issue, we propose the concept of an intermediate deformation buffer that stores deformation information at a resolution independent of the mesh resolution. This allows the combination of a high-resolution buffer with a low-resolution mesh for interactive preview, as well as a high-resolution mesh to export the final image. Further, we present a fully GPU-based implementation of this concept, taking advantage of modern OpenGL ES features, such as compute shaders.

Polygonal models are ubiquitous in computer graphics but their real time manipulation and rendering especially in interactive application environments have become a threat because of their huge sizes and complexity. A whole family of automatic algorithms emerged during the last decade to help out this problem, but they reduce the complexity of the models uniformly without caring about semantic importance of localized parts of a mesh. Only a few algorithms deal with adaptive simplification of polygonal models. We propose a new model for user-driven simplification exploiting the simplification hierarchy and hypertriangulation model [P. Cignoni et al.] that lends a user the most of the functionalities of existing adaptive simplification algorithms in one place and is quite simple to implement. The proposed new underlying data structures are compact and support real time navigation across continuous LODs of a model; any desirable LOD can be extracted efficiently and can further be fine-tuned. The proposed model for adaptive simplification supports two key operations for selective refinement and selective simplification; their effect has been shown on various polygonal models. Comparison with related work shows that the proposed model provides combined environment at reduced overhead of memory space usage and faster running times.

In summary, the aim of this research thesis is to fill a gap left by existing 3D GIS: the generation of a meaningful, interactive, three-dimensional presentation of a selected database, especially in terms of the graphical abstraction and progressive transfer in a heterogeneous network environment. The intention here is to expand the concept of an openly distributed GIS infrastructure of the OpenGIS Consortium (OGC) [BuMc96] to three-dimensional geodata. In contrast to previous work such as [Lang99], the main goal is not to depict a virtual landscape and/or an urban region as photorealistically as possible. Rather, the visual processing of the database should strive to support the user’s information needs. In contrast to computer-graphics rendering, in which a geometric model is depicted on a two-dimensional surface in proper perspective, the goal of the visualization is to transmit information to the user [Fole92]. Apart from the actual rendering, this process also requires a selection procedure that decides which elements of a scene contribute to the information content. This kind of visualization is called graphical abstraction. In a heterogeneous network environment, the problem of resource-adaptive data transfer and visualization is second to the graphical abstraction problem. The question is not only how to suitably describe the selected data, but also how to develop an adequate data transfer that presents the viewer with an initial visual result as quickly as possible. Additional data can be transferred later. This progressive data transfer is crucial for the use of 3D data on the Internet [Ross98]. Core concepts and components of the 3D geodata server developed within this thesis are the development of a query-oriented data model for efficient analysis of topological relations in three-dimensional spatial data, and a method for evaluating the relevance of single feature based on a user specific query. Based on this, a method to generate a graphical abstraction of the query result is developed. In order to compress the resulting model, a compression technique for triangle meshes for progressive transmission is invented. These concepts are proofed by a prototypical implementation within a 3D geodata server.

Visualization of large-scale simulations running on supercomputers requires ultra-high resolution images to capture important features in the data. In this work, we present a system for streaming ultra-high resolution images from a visualization cluster to a remote tiled display at nearly interactive frame rates. vl3, a modular framework for large scale data visualization and analysis, provides the backbone of our implementation. With this system we are able to stream over the network volume renderings of a 20483 voxel dataset at a resolution of 6144×3072 pixels with a frame rate of approximately 3.3 frames per second.

Culling out non-visible portions of 3D scenes is important for rendering large complex worlds at an interactive frame rate. Past 3D engines used static prebaked visibility data which was generated using complex algorithms. Hardware Occlusion Queries are a modern feature that allows engines to determine if objects are invisible on the fly. This allows for fully dynamic destructible and editable environments as opposed to static prebaked environments of the past. This paper presents an algorithm that uses Hardware Occlusion Queries to cull fully dynamic scenes in real-time. This algorithm is relatively simple in comparison to other real-time occlusion culling techniques, making it possible for the average developer to render large detailed scenes. It also requires very little work from the artists who design the scenes since no portals, occluders, or other special objects need to be used.

We propose an interactive visualization approach to finding a mathematical model for a real world process, commonly known in the field of control theory as system identification. The use of interactive visualization techniques provides the modeller with instant visual feedback which facilitates the model validation process. When working interactively with such large data sets, as are common in system identification, methods to handle this data efficiently are required. We are developing approaches based on data streaming to meet this need.

Visual information is taking a predominant place in our society. With the advent of digital technologies, visual information will find new applications in domains ranging from communication, commerce to entertainment. New functionalities will be required that permit an extended interaction with the visual information. In particular, this is the case for digital television and the related problem of video sequence compression. The extent of possible interactions depends on the manner in which the visual information is represented. Up to now, the canonical representation is used. Also referred to as the waveform representation, it is a technical artifact of the image capture procedure. This representation severely restricts the functionalities available to the end-user. The latter is unable to freely manipulate or customize the received visual information. In this dissertation, we propose to describe the visual information through a semantically meaningful representation. This representation directly derives from the scene content, which is decomposed in terms of its constituting objects. Consequently, the viewing process is totally disconnected from the image capture procedure. This permits full interactivity with the visual information, leading to enhanced functionalities for the end-user. The essence of this dissertation is to automatically define the objects forming the scene arid to automatically track them through the video sequence. Two main issues are identified: the initial segmentation of the objects and their tracking. The first issue deals with segmenting the scene into its constituent objects. This has to be performed on the basis of the information available in two consecutive frames. In order to solve the problem, a split-and-merge approach is used. First, the image is segmented into small, spatio-temporally homogeneous regions. This is achieved through a top-down approach where spatial, temporal and change information is combined. These regions are used as a starting point to define the objects forming the scene. A bottom-up approach is used which iteratively merges the regions. The propensity of the regions to form an object is assessed in terms of both spatial and temporal information. The second issue deals with segmenting and tracking the objects in the successive frames. The coherence between the successive segmentations is ensured by using past and current information. Also, the different objects composing the scene are identified throughout the video sequence. This identification relies on temporal, spatial and spatio-temporal features of the objects. The proposed representation of the visual information finds a natural application in video coding. A second generation video coding scheme is presented which combines compression efficiency with extended functionalities. In particular, scalable coding is achieved in terms of both scene content and object coding quality.

In this paper, we address the problem of 3D mesh orientation applied to archaeological fragments coming from a Gothic spire. Initially, these fragments are handled leading to their deterioration while the accuracy of measures (distances, molding shape,. . . ) is not always relevant. To facilitate their study, a 3D acquisition process is applied on these fragments to work on their virtual representations and computerised tools can be proposed. One of them consists in finding the orientation of a 3D mesh. Unfortunately, existing methods provide unexpected results. This is mainly due to the presence of ornamentations we can assimilate to outliers. Therefore, we propose a new method based on the identification of significant areas on the 3D mesh and on the determination of their associated orientation by considering differential parameters. Then, a voting method is performed to identify the orientation appearing the most frequently. Applied on the fragments, we obtain successful results allowing to go further in their analysis.

A method for generating moving, orthogonal, area preserving polygonal meshes