This article presents a novel framework that can generate a high-fidelity isosurface model of X-ray computed tomography (CT) data. CT surfaces with subvoxel precision and smoothness can be simply modeled via isosurfacing, where a single CT value represents an isosurface. However, this inevitably results in geometric distortion of the CT data containing CT artifacts. An alternative is to treat this challenge as a segmentation problem. However, in general, segmentation techniques are not robust against noisy data and require heavy computation to handle the artifacts that occur in three-dimensional CT data. Furthermore, the surfaces generated from segmentation results may contain jagged, overly smooth, or distorted geometries. We present a novel local isosurfacing framework that can address these issues simultaneously. The proposed framework exploits two primary techniques: 1) Canny edge approach for obtaining surface candidate boundary points and evaluating their confidence and 2) screened Poisson optimization for fitting a surface to the boundary points in which the confidence term is incorporated. This combination facilitates local isosurfacing that can produce high-fidelity surface models. We also implement an intuitive user interface to alleviate the burden of selecting the appropriate confidence computing parameters. Our experimental results demonstrate the effectiveness of the proposed framework.

Computerized registration between maxillofacial cone-beam computed tomography (CT) images and a scanned dental model is an essential prerequisite for surgical planning for dental implants or orthognathic surgery. We propose a novel method that performs fully automatic registration between a cone-beam CT image and an optically scanned model. To build a robust and automatic initial registration method, deep pose regression neural networks are applied in a reduced domain (i.e., two-dimensional image). Subsequently, fine registration is performed using optimal clusters. A majority voting system achieves globally optimal transformations while each cluster attempts to optimize local transformation parameters. The coherency of clusters determines their candidacy for the optimal cluster set. The outlying regions in the iso-surface are effectively removed based on the consensus among the optimal clusters. The accuracy of registration is evaluated based on the Euclidean distance of 10 landmarks on a scanned model, which have been annotated by experts in the field. The experiments show that the registration accuracy of the proposed method, measured based on the landmark distance, outperforms the best performing existing method by 33.09%. In addition to achieving high accuracy, our proposed method neither requires human interactions nor priors (e.g., iso-surface extraction). The primary significance of our study is twofold: 1) the employment of lightweight neural networks, which indicates the applicability of neural networks in extracting pose cues that can be easily obtained and 2) the introduction of an optimal cluster-based registration method that can avoid metal artifacts during the matching procedures.

Preintegrated volume rendering produces high-quality renderings without increased sampling rates. However, a look-up table of a conventional preintegrated volume rendering requires a dimensionality of two, which disturbs interactive renderings when the transfer function is changed. Furthermore, as the resolution of the volume data set increases, the memory space required is impractical or inefficient, especially on GPUs. In the past, several approximation methods have been proposed to reduce the complexity of both the time and memory requirement, but most of them do not correctly present thin opaque structures within slabs and ignore the self-attenuation. We propose an advanced interactive preintegrated volume rendering algorithm that achieves not only high-quality renderings comparable to the conventional ones, but also $(O(n))$ time and memory space requirements even with the self-attenuation within the slabs applied. The algorithm proposed in this paper decomposes the exponential term of the ray integration equation into a power series of a finite order in the form of a linear combination to build a one-dimensional look-up table. Moreover, the proposed algorithm effectively applies the self-attenuation that is caused by fully opaque isosurfaces, by introducing an opaque prediction table. Experimental results demonstrate that the proposed algorithm offers renderings visibly identical to existing preintegrated volume renderings without degrading rendering speed.

In this paper we present an interactive query interface called "TrapezoidBox" to support spatial proximity queries where users' degree of interest varies depending upon the degree of separation from the point of interest. Spatial proximity queries are commonly built in information seeking tasks especially on online maps. If not impossible, it is hard to formulate spatial proximity queries using existing dynamic query widgets such as range sliders. TrapezoidBox allows users to easily build spatial proximity queries by interactively adjusting a trapezoidal function. Our controlled user study results show that TrapezoidBox has several advantages over a baseline interface with range sliders.

Volume ray-casting with a higher order reconstruction filter and/or a higher sampling rate has been adopted in direct volume rendering frameworks to provide a smooth reconstruction of the volume scalar and/or to reduce artifacts when the combined frequency of the volume and transfer function is high. While it enables high-quality volume rendering, it cannot support interactive rendering due to its high computational cost. In this paper, we propose a fast high-quality volume ray-casting algorithm which effectively increases the sampling rate. While a ray traverses the volume, intensity values are uniformly reconstructed using a high-order convolution filter. Additional samplings, referred to as virtual samplings, are carried out within a ray segment from a cubic spline curve interpolating those uniformly reconstructed intensities. These virtual samplings are performed by evaluating the polynomial function of the cubic spline curve via simple arithmetic operations. The min max blocks are refined accordingly for accurate empty space skipping in the proposed method. Experimental results demonstrate that the proposed algorithm, also exploiting fast cubic texture filtering supported by programmable GPUs, offers renderings as good as a conventional ray-casting algorithm using high-order reconstruction filtering at the same sampling rate, while delivering 2.5x to 3.3x rendering speed-up.

Abstract In this paper, we propose a GPU‐based volume ray casting for virtual colonoscopy to generate high‐quality rendering images with a large screen size. Using the temporal coherence for ray casting, the empty space leaping can be efficiently done by reprojecting first‐hit points of the previous frame; however, these approaches could produce artifacts such as holes or illegal starting positions due to the insufficient resolution of first‐hit points. To eliminate these artifacts, we use a triangle mesh of first‐hit points and check the intersection of each triangle with the corresponding real surface. Illegal starting positions can be avoided by replacing a false triangle cutting the real surface with five newly generated triangles. The proposed algorithm is best fit to the recent GPU architecture withShader Model 4.0which supports not only fast rasterization of a triangle mesh but also many flexible vertex operations. Experimental results on ATI 2900 with DirectX10 show perspective volume renderings of over 24fps on 1024 × 1024 screen size without any loss of image quality. Copyright © 2008 John Wiley & Sons, Ltd.

Shear–warp volume rendering has the advantages of a moderate image quality and a fast rendering speed. However, in the case of dynamic changes in the opacity transfer function, the efficiency of memory access drops, as the method cannot exploit pre-classified volumes. In this paper, we propose an efficient algorithm that exploits the spatial locality of memory references for interactive classifications. The algorithm inserts a rotation matrix when factorizing the viewing transformation, so that it may perform a scanline-based traversal in both object space and image space. In addition, we present solutions to some problems of the proposed method, namely inaccurate front-to-back composition, the occurrence of holes, and increased computation. Our method is noticeably faster than traditional shear-warp rendering methods because of an improved utilization of cache memory. Copyright © 2005 John Wiley & Sons, Ltd.

Abstract Interactive display of complex scenes is a challenging problem in computer graphics. Such current approaches as z‐buffer, level of detail and visibility culling have not fully used the temporal coherence between consecutive frames. When the viewing condition is fixed, the color and depth values of static polygons can be obtained from the result of the previous frame and only the remaining dynamic polygons require rendering. We present a method that enhances the speed of the conventional z‐buffer algorithm by exploiting the above temporal coherence. This algorithm is simple to combine with existing graphics hardware that supports the conventional z‐buffer algorithm. It can manipulate any scene suitable for the z‐buffer algorithm without preprocessing or human intervention. The rendering time is proportional to the number of dynamic polygons in each frame. Experimental results show that our method is faster than the conventional z‐buffer algorithm and the performance enhancement becomes higher as the fraction of static polygons increases. Copyright © 2001 John Wiley & Sons, Ltd.

This paper presents a role-based decomposition model for improving concurrency in distributed object-oriented software development environments. In software development process, the target software system consists of a large number of components closely related with one another. This results in potential operation conflicts in cooperative works among the project members. This problem can be much reduced by decomposing the target software system into the relatively independent components. Our system incorporates hierarchical role-based decomposition model to reduce operation conflicts frequently occur in synchronous/asynchronous collaboration. The decomposed components are also used as basic units of the role-based access control. Once the target software system is properly decomposed according to this model, its subsystems can migrate to the other sites, and thus, the components can be evenly distributed over networked computers.

Since volume rendering needs a lot of computation time and memory space, many researches have been suggested for accelerating rendering or reducing data size using compression techniques. However, there is little progress in a research for accomplishing these goals. This paper presents an efficient wavelet-based compression method providing fast visualization of large volume data, which is divided into individual blocks with regular resolution. Wavelet transformed block is runlength encoded in accordance with the reconstruction order resulting in a fairly good compression ratio and fast reconstruction. A cache data structure is designed to speed up the reconstruction, and an adaptive compression scheme is proposed to produce a higher quality rendered image. The compression method proposed here is combined with several accelerated volume rendering algorithms, such as brute-force volume rendering with min-max table and Lacroute's shear-warp factorization. Experimental results have shown the space requirement to be about 1/27 and the rendering time to be about 3 seconds for 512/spl times/512/spl times/512 data sets while preserving the quality of an image much like using the original data.

Stereoscopic volume rendering provides powerful depth information, but it takes a long time to render two-eye images. Previous algorithms based on reprojection methods project the result of one view of a stereo pair into the other instead of rendering a new one completely. Because of inaccurate mapping between the two images, the quality of the reprojected image is not satisfactory. This paper presents a new algorithm to preserve the accuracy of both images with very little increase in computation time. The efficiency of the new algorithm comes from the use of ray templates and object-order processing. This algorithm makes two different templates for each eye and renders two images simultaneously, tracing the volume only once in object order. We also extend the algorithm to support image-space supersampling by using more ray templates. Experimental results show that the image quality of the new algorithm is not only comparable with that of ray casting but also the rendering speed is near that of the interactive shear–warp algorithm employing object-order processing and spatial data coherency. Copyright © 1999 John Wiley & Sons, Ltd.

The paper presents an efficient image based rendering algorithm of volume data. Using intermediate image space instead of image space, mapping becomes more efficient and holes coming from the point-to-point mapping can be removed. Mapping in intermediate image space is easily performed by looking up the table with the depth value of a source pixel. We also suggest a way of minimizing space requirement for pre-acquired images. Experimental results show that the algorithm can generate 25-40 images per second without noticeable image degradation in the case of making 256/sup 2/ images with a 256/sup 3/ voxel data set.

Template-based volume rendering is a technique to accelerate volume ray casting. It does not trade off image quality for rendering speed. However, it still falls short of interactive manipulation of volume data, mainly owing to the ray-by-ray volume access pattern and the long ray path in the transparent regions. In this paper we present an object-order template-based volume rendering method that uses run-length encoding to enable skipping highly transparent regions. We present three algorithms, one for each principal axis direction. By combining the advantages of object-order volume traversal and run-length encoded volumes, the algorithms achieve high quality rendering in a much shorter time than the original template-based volume rendering. © 1998 John Wiley & Sons, Ltd.

The object-oriented method has become very popular in software development because of its efficiency in automating software development processes and reusing software modules. To date, various object-oriented CASE tools have been used. However, they have concentrated on providing tools for developing software systems within some particular area. Even though we can use a general-purpose CSCW tool for cooperative software development in a distributed environment, current CSCW systems do not support any efficient object-oriented software development method. This paper discusses ways of combining CSCW features with an object-oriented CASE tool by introducing the experimental distributed object-oriented software development environment DOOD (Distributed Object-Oriented Designer). DOOD supports three models (the object model, the dynamic model and the functional model) of OMT (Object Modeling Technique) and provides consistent and transparent user interfaces for minimizing the effects of a geographically dispersed development environment. Our system is implemented based on a client-server architecture. The DOOD/Server manages the communication among clients and guarantees concurrent and consistent accesses to all the objects in the central repository, while DOOD/Client provides modeling and collaboration schemes over a TCP/IP network.

Template-based volume rendering is an acceleration technique for volume ray casting. It does not trade-off the image quality for the rendering speed. However, it still falls short of interactive manipulation of volume data, mainly due to the ray-by-ray volume access pattern and the long ray path in the transparent regions. In this paper, we present an object-order template-based volume rendering method that uses run-length encoding to enable the skipping of highly transparent regions. We present three algorithms, one for each principal axis direction. By combining the advantages of object-order volume traversal and run-length encoded volumes, the algorithms achieve high-quality rendering in a much shorter time than the original template-based volume rendering.

Ray casting may be applied to the terrain rendering from DTMs (digital terrain models). In this paper we propose a ray casting method which exploits exact vertical ray coherence. This method not only achieves a good performance, but also allows any set of viewing parameters. To analyse the vertical ray coherence property, we define the following terms: a ray plane which is perpendicular to the sea-level plane and passes through the COP (centre of projection), and the corresponding ray line which is the line of intersection of the ray plane and the projection plane. Vertical ray coherence can be stated as: if two rays pass through the same ray line, they pass over the identical set of points on the DTM base plane. After a ray is cast on the DTM, we can get a good starting point to cast another ray using this property. Our method tries to cover the projection plane with ray lines. Since ray lines are not parallel to each other, it is a difficult task to cover the entire plane. In fact all ray lines intersect at a point (COP′). We first generate a set of ray lines sufficient to cover the projection plane near COP′. As pixels get further from COP′, more ray lines are generated to fill most of the gaps between pixels covered by the previous set of ray lines. Rays passing through the same ray line are effectively cast using vertical ray coherence. To fill remaining pixels not covered by ray lines, pixel values of vertical/horizontal neighbours are interpolated. To cast rays efficiently, successive points generated by a line algorithm are followed along the projection of the rays on the DTM base plane. © 1997 by John Wiley & Sons, Ltd.

To visualize the volume data acquired from computation or sampling, it is necessary to estimate normals at the points corresponding to object surfaces. Volume data does not holds the geometric information for the surface comprising points, so it is necessary to calculate normals using local information at each point. The existing normal estimation methods have some problems of estimating incorrect normals at discontinuous, aliased or noisy points. Yagel et al. (1992) solved some of these problems using their context-sensitive method. However, this method requires too much processing time and it loses some information on detailed parts of the object surfaces. This paper proposes the surface-characteristic-sensitive normal estimation method which applies different operators according to characteristics of each surface for the normal calculation. This method has the same advantages of the context-sensitive method, and also some other advantages such as less processing time and the reduction of the information loss on detailed parts.

A method is presented for the automatic determination of assembly partial orders from a liaison graph representation of an assembly through the extraction of preferred subassemblies. In particular, the authors show how to select a set of tentative subassemblies by decomposing a liaison graph into a set of subgraphs based on feasibility and difficulty of disassembly, how to evaluate each of the tentative subassemblies in terms of assembly cost using the subassembly selection indices, and how to construct a hierarchical partial order graph as an assembly plan. The method provides an approach to assembly planning by identifying spatial parallelism in assembly as a means of constructing temporal relationships among assembly operations and solves the problem of finding a cost-effective assembly plan in flexible environment. A case study of the assembly planning of a mechanical assembly is presented.>