基于桶内动态融合的透明现象的高效绘制

基于桶排序的顺序独立透明现象绘制算法,采用桶排序原理将投影收集到同一个像素上的多个片元并排序,当发生桶内片元冲突时会产生错误的绘制结果.为此,提出一种基于桶内动态融合的透明现象的高效绘制算法.此算法采用桶内动态融合和并发读/写的方法逐一融合落入同一个桶内的所有片元,并在后处理中按从前向后的顺序融合各个桶内的颜色值.由于同时发生桶内片元冲突和读/写冲突的概率非常小,因而可以大大提高绘制结果的准确性.实验结果表明,与基于桶排序的绘制算法相比,采用文中算法可以更准确地绘制场景,生成与真实结果非常相近的绘制效果,同时算法的效率基本保持不变.

工程地质三维建模与可视化技术应用开发

Synthetic Geology Information System (SGIS) is an important constituent part of the theory of Engineering Geomechanics Mate-Synthetic (EGMS), and is the information system more suited for the collection, storage, management, analysis and processing to the information coming from engineering geology,' geological engineering and geotechnical engineering. Its contents involve various works and methods of the investigation, design, and construction in different stages of the geological engineering. Engineering geological and three-dimensional modeling and visualization is the fundamental part of the SGIS, and is a theory, method and technique by which, adopting the computer graphics and image processing techniques, the data derived from engineering geological survey and the calculated results obtained from the geomechanical numerical simulation and analysis are converted to the graphics and images displayed on the computer screen and can be processed interactively. In this paper, the significance and realizing approaches of the three-dimensional modeling and visualization for the complex geological mass in the engineering geology are discussed and the methods of taking advantage of the interpolation and fitting for the scattered and field-surveyed data to simulate the geological layers, such as the topography and earth surface, the groundwater table and the stratum boundary, are researched into. At the mean time, in mind the characteristics of the structure of the basic data for three-dimensional modeling, its visual management can be resolved into the engineering surveyed database management module, plot parameter management module and data output module and the requirement for basic data management can be fulfilled. In the paper, the establishment and development of the three-dimensional geological information system are probed tentatively, and an instance of three-dimensional visual Engineering Distribution Information System (EDIS), theConstruction Management Information System for an airport, in which the functions, such as the real-time browse among the three-dimensional virtual-reality landscapes of the airport construction from start to finish, the information query to the airport facility and the building in the housing district and the recording and playback of the animation sets for the browse and the takeoff and landing of the planes, is developed by applying the component-mode three-dimensional virtual-reality geological information system (GIS) software development kits (SDK), so the three-dimensional visual management platform is provided for the airport construction. Moreover, in the gaper, integrated with the three-dimensional topography visualization and its application in the Sichuan-Tibet Highways, the method of the digital elevation model (DEM) data collection from the topographic maps is described, and the three-dimensional visualization and the roaming about the terrain along the highway are achieved through computer language programming. Understanding to the important role played by the varied and unique topographical condition in the gestation and germination of the highly-dense, frequently-arising and severely-endangered geological hazards can be deepened.

地震勘探三维可视化方法研究与实现

This thesis mainly studies the technologies of 3-D seismic visualization and Graphic User Interface of seismic processing software. By studying Computer Graphics and 3-D geological modeling, the author designs and implements the visualization module of seismic data processing software using OpenGL and Motif. Setting seismic visualization flow as the subject, NURBS surface approximation and Delaunay Triangulation as the two different methods, the thesis discusses the key algorithms and technologies of seismic visualization and attempts to apply Octree Space Partitioning and Mip Mapping to enhance system performance. According to the research mentioned above, in view of portability and scalability, the author adopts Object-oriented Analysis and Object-oriented Design, uses standard C++ as programming language, OpenGL as 3-D graphics library and Motif as GUI developing tool to implement the seismic visualization framework on SGI Irix platform. This thesis also studies the solution of fluid equations in porous media. 2-D alternating direction implicit procedure has been turned into 3-D successive over relaxation iteration, which possesses such virtues as faster computing speed, faster convergence rate, better adaptability to heterogeneous media and less memory demanding.

Estimation of Pose and Illuminant Direction for Face Processing

In this paper three problems related to the analysis of facial images are addressed: the illuminant direction, the compensation of illumination effects and, finally, the recovery of the pose of the face, restricted to in-depth rotations. The solutions proposed for these problems rely on the use of computer graphics techniques to provide images of faces under different illumination and pose, starting from a database of frontal views under frontal illumination.

The Specialized Mappings Architecture

A probabilistic, nonlinear supervised learning model is proposed: the Specialized Mappings Architecture (SMA). The SMA employs a set of several forward mapping functions that are estimated automatically from training data. Each specialized function maps certain domains of the input space (e.g., image features) onto the output space (e.g., articulated body parameters). The SMA can model ambiguous, one-to-many mappings that may yield multiple valid output hypotheses. Once learned, the mapping functions generate a set of output hypotheses for a given input via a statistical inference procedure. The SMA inference procedure incorporates an inverse mapping or feedback function in evaluating the likelihood of each of the hypothesis. Possible feedback functions include computer graphics rendering routines that can generate images for given hypotheses. The SMA employs a variant of the Expectation-Maximization algorithm for simultaneous learning of the specialized domains along with the mapping functions, and approximate strategies for inference. The framework is demonstrated in a computer vision system that can estimate the articulated pose parameters of a human’s body or hands, given silhouettes from a single image. The accuracy and stability of the SMA are also tested using synthetic images of human bodies and hands, where ground truth is known.

Model and visualise the relationship between energy consumption and temperature distribution in cold rooms

In the area of food and pharmacy cold storage, temperature distribution is considered as a key factor. Inappropriate distribution of temperature during the cooling process in cold rooms will cause the deterioration of the quality of products and therefore shorten their life-span. In practice, in order to maintain the distribution of temperature at an appropriate level, large amount of electrical energy has to be consumed to cool down the volume of space, based on the reading of a single temperature sensor placed in every cold room. However, it is not clear and visible that what is the change of energy consumption and temperature distribution over time. It lacks of effective tools to visualise such a phenomenon. In this poster, we initially present a solution which combines a visualisation tool with a Computational Fluid Dynamics (CFD) model together to enable users to explore such phenomenon.

Electromagnetic tracking and steering for catheter navigation

This thesis explores the use of electromagnetics for both steering and tracking of medical instruments in minimally invasive surgeries. The end application is virtual navigation of the lung for biopsy of early stage cancer nodules. Navigation to the peripheral regions of the lung is difficult due to physical dimensions of the bronchi and current methods have low successes rates for accurate diagnosis. Firstly, the potential use of DC magnetic fields for the actuation of catheter devices with permanently magnetised distal attachments is investigated. Catheter models formed from various materials and magnetic tip formations are used to examine the usefulness of relatively low power and compact electromagnets. The force and torque that can be exerted on a small permanent magnet is shown to be extremely limited. Hence, after this initial investigation we turn our attention to electromagnetic tracking, in the development of a novel, low-cost implementation of a GPS-like system for navigating within a patient. A planar magnetic transmitter, formed on a printed circuit board for a low-profile and low cost manufacture, is used to generate a low frequency magnetic field distribution which is detected by a small induction coil sensor. The field transmitter is controlled by a novel closed-loop system that ensures a highly stable magnetic field with reduced interference from one transmitter coil to another. Efficient demodulation schemes are presented which utilise synchronous detection of each magnetic field component experienced by the sensor. The overall tracking accuracy of the system is shown to be less than 2 mm with an orientation error less than 1°. A novel demodulation implementation using a unique undersampling approach allows the use of reduced sample rates to sample the signals of interest without loss of tracking accuracy. This is advantageous for embedded microcontroller implementations of EM tracking systems. The EM tracking system is demonstrated in the pre-clinical environment of a breathing lung phantom. The airways of the phantom are successfully navigated using the system in combination with a 3D computer model rendered from CT data. Registration is achieved using both a landmark rigid registration method and a hybrid fiducial-free approach. The design of a planar magnetic shield structure for blocking the effects of metallic distortion from below the transmitter is presented which successfully blocks the impact of large ferromagnetic objects such as operating tables. A variety of shielding material are analysed with MuMetal and ferrite both providing excellent shieling performance and an increased signal to noise ratio. Finally, the effect of conductive materials and human tissue on magnetic field measurements is presented. Error due to induced eddy currents and capacitive coupling is shown to severely affect EM tracking accuracy at higher frequencies.

Comparative performance of multiview stereoscopic and mammographic display modalities for breast lesion detection.

PURPOSE: Mammography is known to be one of the most difficult radiographic exams to interpret. Mammography has important limitations, including the superposition of normal tissue that can obscure a mass, chance alignment of normal tissue to mimic a true lesion and the inability to derive volumetric information. It has been shown that stereomammography can overcome these deficiencies by showing that layers of normal tissue lay at different depths. If standard stereomammography (i.e., a single stereoscopic pair consisting of two projection images) can significantly improve lesion detection, how will multiview stereoscopy (MVS), where many projection images are used, compare to mammography? The aim of this study was to assess the relative performance of MVS compared to mammography for breast mass detection. METHODS: The MVS image sets consisted of the 25 raw projection images acquired over an arc of approximately 45 degrees using a Siemens prototype breast tomosynthesis system. The mammograms were acquired using a commercial Siemens FFDM system. The raw data were taken from both of these systems for 27 cases and realistic simulated mass lesions were added to duplicates of the 27 images at the same local contrast. The images with lesions (27 mammography and 27 MVS) and the images without lesions (27 mammography and 27 MVS) were then postprocessed to provide comparable and representative image appearance across the two modalities. All 108 image sets were shown to five full-time breast imaging radiologists in random order on a state-of-the-art stereoscopic display. The observers were asked to give a confidence rating for each image (0 for lesion definitely not present, 100 for lesion definitely present). The ratings were then compiled and processed using ROC and variance analysis. RESULTS: The mean AUC for the five observers was 0.614 +/- 0.055 for mammography and 0.778 +/- 0.052 for multiview stereoscopy. The difference of 0.164 +/- 0.065 was statistically significant with a p-value of 0.0148. CONCLUSIONS: The differences in the AUCs and the p-value suggest that multiview stereoscopy has a statistically significant advantage over mammography in the detection of simulated breast masses. This highlights the dominance of anatomical noise compared to quantum noise for breast mass detection. It also shows that significant lesion detection can be achieved with MVS without any of the artifacts associated with tomosynthesis.

Investigating shape-from-shading illusions using solid objects

Recent growth in the shape-from-shading psychophysics literature has been paralled by an increasing availability of computer graphics hardware and software, to the extent that most psychophysical studies in this area now employ computer lighting algorithms. The most widely used of algorithms is shape-from-shading psychophysics is the Phong lighting model. This model, and other shading models of its genre, produce readily ineterpretable imiages of three-dimensional scenes. However, such algorithms are only approximations of how light interacts with real objects in the natural environment. Nevertheless, the results from psychophysical experiments using these techniques have been used to infer the processes underlying the perception of shape-from-shading in natural environments. It is important to establish whether this substitution is ever valid. We report a series of experiments investigating whether two recently reported illusions seen computer-generated, Phond shaded images occur for solid objects under real illuminants. The two illusions investigated are three-dimensional curvature contrast and the illuminant-position effect on perceived curvature. We show that both effects do occur for solid objects, and that the magnitude of these effects are equivalent regardless of whether subjects are presented with ray traced or solid objects.

BSP -Style Computation: A Semantic Investigation

A BSP (Bulk Synchronous Parallelism) computation is characterized by the generation of asynchronous messages in packages during independent execution of a number of processes and their subsequent delivery at synchronization points. Bundling messages together represents a significant departure from the traditional ‘one communication at a time’ approach. In this paper the semantic consequences of communication packaging are explored. In particular, the BSP communication structure is identified with a general form of substitution—predicate substitution. Predicate substitution provides a means of reasoning about the synchronized delivery of asynchronous communications when the immediate programming context does not explicitly refer to the variables that are to be updated (unlike traditional operations, such as the assignment $x := e$, where the names of the updated variables can be extracted from the context). Proofs of implementations of Newton's root finding method and prefix sum are used to illustrate the practical application of the proposed approach.