基于图像建模技术研究综述与展望

基于图像建模技术是计算机图形学和计算机视觉领域共同关心的重要问题．文中侧重从计算机图形学的研究角度对基于图像建模技术进行了综述,介绍了近年来提出的典型的基于图像建模方法及其最新研究进展,给出了这些方法的基本原理并加以分析比较,最后对基于图像建模技术的未来研究给出了一些建议。     

数学建模驱动的“计算机图形学”课堂教学模式改革

计算机图形学是计算机科学与技术、数字媒体技术等高校本科专业的主干核心专业课程。由于涉及较多的数学与算法基础,它一直是困扰计算机科学与技术专业学生的课程之一。本校“计算机图形学”课程组在教学实践中,创造性地将图形学的核心教学内容分解为若干个数学建模问题,然后在授课教师的启发和指导下,学生分组讨论,求解相应的数学建模问题。以数学建模的视角对计算机图形学课程教学模式进行改革,它不仅加深了学生对相关教学内容问题本质的理解,而且使学生以更加积极主动的姿态投入到对图形学的学习与研究之中。     

海浪建模与绘制技术综述*

海浪建模和绘制技术成为计算机图形学和虚拟现实领域共同关心的自然现象模拟问题.侧重从计算机图形学的研究角度对海浪建模和绘制技术进行了综述,介绍了近二十年来提出的典型海浪建模和绘制方法及其最新研究进展,给出了这些方法的基本原理并加以分析比较,最后对海浪建模和绘制技术的未来研究给出了一些建议.     

树的建模技术研究综述与展望

树的建模技术是计算机图形学近年来研究的热点问题之一.侧重从计算机图形学的研究角度,对树的建模技术分别从基于规则的树建模技术、基于草图的树建模技术、基于图像的树建模技术3个方面进行了总结和综述,介绍了近年来提出的典型的树建模方法及最新研究进展,对其中涉及的关键技术进行了总结分析,给出了这些技术的基本思想、局限性和使用范围,并加以分析比较,最后对树的建模技术的未来研究方向给出展望.     

虚拟现实在计算机图形学课程中的实验探索

虚拟现实技术与计算机图形学相辅相成,为使计算机图形学的实验开设更具实际应用意义,该文提出基于VRML、基于三维建模技术和基于Web3D技术的三种VR实现方法,并通过实例分析了该三种方法的应用特点。     

论三维人脸建模技术的应用

建立三维人脸模型和表情动画是计算机图形学领域的一个研究热点,本文分析了三维人脸建模技术研究的现状,论证了三维人脸建模技术在虚拟现实、影视制作、计算机辅助教学、可视电话、视频会议、医学研究、游戏娱乐等诸多方面,都具有很强的应用价值。提出了三维人脸建模技术研究方法。     

人体几何建模方法综述

人体建模是计算机图形学与计算机视觉领域的重要研究课题,而人体几何建模则是人体建模的基础。人体几何建模技术发展至今,已经出现了大量的实现方法。回顾和总结了人体几何建模领域一些最新的研究成果,将其分为直接建模方法、2D图片识别方法、模板匹配方法、统计综合建模4大类,并且对人体几何建模方法的未来发展趋势进行了展望。     

VRML与3DS MAX 建模的互补性研究

三维建模和虚拟现实技术都是近些年来随着计算机图形学的发展而日渐成熟的新兴技术,基于互联网的虚拟现实技术已经越来越成为计算机图形学领域的新课题之一。如今应用在三维建模类的软件种类繁多,不同的软件功能也各具特色。为了快速实现三维模型建立并实现网络浏览,可根据3DS MAX提供的可视的三维建模能力,以及VRML虚拟现实三维立体网络程序语言,构造虚拟场景并实现用户与虚拟场景的网络浏览。介绍了3DS MAX与VRML语言的相关技术特点,并通过实例使用3DS MAX和VRML语言进行建模,实现虚拟交互的快捷方法。通过对VRML与3DS MAX建模的互补研究,解决了快速建模并实现虚拟场景的网络浏览。     

三维动画中常用计算机图形学知识的教学探究

在艺术院校,学生缺乏一些应有计算机图形学的了解,使其以机械记忆的方式学习三维动画软件,而不知其原理,操作时有较大盲目性,也很难发挥软件的一些高级功能。三维动画中常用计算机图形学是学好三维动画必备知识。但计算机图形学抽象,对理性思维较弱的艺术院校学生来说,易产生理解困难,甚至反感抵触。文章结合计算机图形学的特性和艺术院校学生的特点,对艺术院校三维动画中常用计算机图形学的教学内容和原则进行论述。     

可微绘制技术研究进展

可微绘制技术是当前虚拟现实、计算机图形学与计算机视觉领域研究的热点,其目标是改造计算机图形学中以光栅化或光线跟踪算法为主的真实感绘制流程,支持梯度信息回传以计算由输出图像的变化导致的输入几何、材质属性变化,通过与优化及深度学习技术等相结合支持从数据中学习绘制模型和逆向推理,是可微学习技术在计算机图形学绘制技术中的应用的具体体现,在增强/虚拟现实内容生成、三维重建、表观采集建模和逆向光学设计等领域中有广泛的应用前景。本文对可微绘制当前的发展状况进行调研,重点对该技术在真实感绘制、3维重建和表观采集建模中的研究和应用情况进行综述,并对可微绘制技术发展趋势进行展望,以期推动可微技术在学术界和产业界的进一步发展。     

A Survey of Volumetric Illumination Techniques for Interactive Volume Rendering

Interactive volume rendering in its standard formulation has become an increasingly important tool in many application domains. In recent years several advanced volumetric illumination techniques to be used in interactive scenarios have been proposed. These techniques claim to have perceptual benefits as well as being capable of producing more realistic volume rendered images. Naturally, they cover a wide spectrum of illumination effects, including varying shading and scattering effects. In this survey, we review and classify the existing techniques for advanced volumetric illumination. The classification will be conducted based on their technical realization, their performance behaviour as well as their perceptual capabilities. Based on the limitations revealed in this review, we will define future challenges in the area of interactive advanced volumetric illumination.     

A B-spline based framework for volumetric object modeling

With the recent development of Iso-geometric Analysis (IGA) (Cottrell et al., 2009) and advanced manufacturing technologies employing heterogeneous materials, such as additive manufacturing (AM) of functionally graded material, there is a growing emerging need for a full volumetric representation of 3D objects, that prescribes the interior of the object in addition to its boundaries. In this paper, we propose a volumetric representation (V-rep) for geometric modeling that is based on trimmed B-spline trivariates and introduce its supporting volumetric modeling framework. The framework includes various volumetric model (V-model) construction methods from basic non-singular volumetric primitives to high level constructors, as well as Boolean operations’ support for V-models. A V-model is decomposed into and defined by a complex of volumetric cells (V-cells), each of which can also represent a variety of additional varying fields over it, and hence over the entire V-model. With these capabilities, the proposed framework is able of supporting volumetric IGA needs as well as represent and manage heterogeneous materials for AM. Further, this framework is also a seamless extension to existing boundary representations (B-reps) common in all contemporary geometric modeling systems, and allows a simple migration of existing B-rep data, tools and algorithms. Examples of volumetric models constructed using the proposed framework are presented.     

ShapeGenetics: Using Genetic Algorithms for Procedural Modeling

In this paper, we show that genetic algorithms (GA) can be used to control the output of procedural modeling algorithms. We propose an efficient way to encode the choices that have to be made during a procedural generation as a hierarchical genome representation. In combination with mutation and reproduction operations specifically designed for controlled procedural modeling, our GA can evolve a population of individual models close to any high‐level goal. Possible scenarios include a volume that should be filled by a procedurally grown tree or a painted silhouette that should be followed by the skyline of a procedurally generated city. These goals are easy to set up for an artist compared to the tens of thousands of variables that describe the generated model and are chosen by the GA. Previous approaches for controlled procedural modeling either use Reversible Jump Markov Chain Monte Carlo (RJMCMC) or Stochastically‐Ordered Sequential Monte Carlo (SOSMC) as workhorse for the optimization. While RJMCMC converges slowly, requiring multiple hours for the optimization of larger models, it produces high quality models. SOSMC shows faster convergence under tight time constraints for many models, but can get stuck due to choices made in the early stages of optimization. Our GA shows faster convergence than SOSMC and generates better models than RJMCMC in the long run.     

Visualizing Stars and Emission Nebulas

We describe star and nebula visualization techniques used to create a 3D volumetric visualization of the Orion Nebula. The nebula's ionization layer is modeled first as a surface model, derived from infrared and visible light observations. The surface model is imported into a volume scene graph-based visualization system that uses procedural volume modeling to simulate the nebula's emissive gas layers. Additional scene graphs model proplyds and shock fronts within the nebula. Stars are rendered using Gaussian spots that are attenuated with distance. Finally, eighty-six separate volumes are voxelized from these scene graphs, then simultaneously volume rendered.     

Using graph rewriting methods for the semi-automatic generation of parametric infrastructure models

For the design of large infrastructure projects such as inner-city subway tracks, it proves necessary to consider differing model scales, ranging from the scale of several kilometers down to a few millimeters. This challenge can be addressed by using multi-scale product models comprising multiple levels of detail (LoD). Ensuring consistency across the different LoDs can be achieved by applying procedural and parametric modeling techniques while creating the model. This results in a flexible multi-scale model that can be easily modified on one scale while other scales are automatically updated. However, the correct application of parametric constraints and procedural dependencies has shown to be a very complex and time-consuming process. To address this issue, this papers presents a semi-automated detailing mechanism, which is based on formal procedures based on graphs and graph transformations. This paper discusses how procedural parametric models based on two-dimensional sketches can be represented by graphs and how detailing steps in the form of parametric modeling operations can be formalized by using rule-based graph rewriting.     

A method to exchange procedurally represented 2D CAD model data using ISO 10303 STEP

Procedural models have the advantage of being easy to edit simply by changing the values of the parameters of their constructional operations. Such models are said to embody design intent, in the sense that modifications to them conform to the method of creation used by their original creator. They also comply with any constraints implied by the particular constructional operations used. This paper introduces the development and standardization process of the ISO 10303-112 specification and describes the concept of procedural 2D modeling, a method of representing procedural 2D CAD models in STEP in harmony with other STEP resources. The feasibility of procedural 2D modeling commands for the exchange of procedurally represented 2D CAD model data is demonstrated through an experiment where procedural 2D CAD model data in neutral form generated with an in-house 2D modeling system are translated to and modified in a commercial 3D mechanical CAD system.     

Procedural approach to volumetric terrain generation

The recent outbreak of indie games has popularized volumetric terrains to a new level, although video games have used them for decades. These terrains contain geological data, such as materials or cave systems. To improve the exploration experience and due to the large amount of data needed to construct volumetric terrains, industry uses procedural methods to generate them. However, they use their own methods, which are focused on their specific problem domains, lacking customization features. Besides, the evaluation of the procedural terrain generators remains an open issue in this field since no standard metrics have been established yet. In this paper, we propose a new approach to procedural volumetric terrains. It generates completely customizable volumetric terrains with layered materials and other features (e.g., mineral veins, underground caves, material mixtures and underground material flow). The method allows the designer to specify the characteristics of the terrain using intuitive parameters. Additionally, it uses a specific representation for the terrain based on stacked material structures, reducing memory requirements. To overcome the problem in the evaluation of the generators, we propose a new set of metrics for the generated content.     

Volume splitting and its applications

Splitting a volumetric object is a useful operation in volume graphics and its applications, but is not widely supported by existing systems for volume-based modeling and rendering. In this paper, we present an investigation into two main algorithmic approaches, namely, explicit and implicit splitting, for modeling and rendering splitting actions. We consider a generalized notion based on scalar fields, which encompasses discrete specifications (e.g., volume data sets) as well as procedural specifications (e.g., hypertextures) of volumetric objects. We examine the correctness, effectiveness, efficiency, and deficiencies of each approach in specifying and controlling a spatial and temporal specification of splitting. We propose methods for implementing these approaches and for overcoming their deficiencies. We present a modeling tool for creating specifications of splitting functions, and describe the use of volume scene graphs for facilitating direct rendering of volume splitting. We demonstrate the use of these approaches with examples of volume visualization, medical illustration, volume animation, and special effects     

Comparison and evaluation of goal-oriented satisfaction analysis techniques

Goal-oriented requirements engineering (GORE) has been introduced as a means of modeling and understanding the motivations for system requirements. Using models to make goals explicit helps to avoid system failures due to implementing the wrong requirements or ignoring certain stakeholder needs. These models are unique when compared to other models used in system analysis in that their structure naturally lends itself to an analysis of goal satisfaction. Existing work claims that analysis using goal models can facilitate decision making over functional or design alternatives, using criteria in the model. Many different approaches to the analysis of goal-oriented requirements models have been proposed, including several procedures that analyze the satisfaction or denial of goals. These procedures make different choices in their interpretation of the goal model syntax, the methods to resolve conflicting or partial evidence, and in the way they represent satisfaction. This work uses three available tools implementing seven similar goal satisfaction analysis procedures to analyze three sample goal models. Results are reported and compared. The purpose of this comparison is to understand the ways in which procedural design choices affect analysis results, and how differences in analysis results could lead to different recommendations over alternatives in the model. Our comparison shows that different satisfaction analysis techniques for goal models can produce variable results, depending on the structure of the model. Comparison findings lead us to recommend the use of satisfaction analysis techniques for goal models as only heuristics for decision making. Our results emphasize investigation into the benefits of satisfaction analysis beyond decision making, namely improving model quality, increasing domain knowledge, and facilitating communication.