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题名:
植物老化过程模拟研究
作者: 迟小羽
答辩日期: 2009-02-06
授予单位: 中国科学院软件研究所
授予地点: 软件研究所
学位: 博士
关键词: 真实感绘制 ; 物理模拟 ; 质点弹簧模型 ; 老化度 ; 完全老化空间 ; 纹理合成 ; BRDF ; BTDF ; 线性光源 ; 采集
其他题名: Study on Weathering of Plants
摘要: 植物老化过程模拟包括物体表观采集技术是如今计算机图形学的热点研究内容,它在理论研究以及实际应用两方面都具有重要意义。本文对此领域中的问题进行了深入研究与探讨,取得了一定的研究成果。 植物的老化模拟和真实感绘制技术一直是图形学中一个富有挑战性的问题,它对于让计算机中真实表现自然物体和场景起着不可或缺的作用。随着研究与应用的深入,植物的真实感仿真程度越来越成为研究者关注的重点。人们力图从几何形状和表观纹理等多方面提高虚拟植物的真实感,以满足应用的要求。本文即针对植物老化过程的模拟方法进行了研究,提出了基于物理模拟的叶子构型,完全老化空间方法,以及合成叶子表观等方面的一系列解决方法。这些方法与技术为自然场景中植物的真实绘制创造了条件,具有很强的实用价值。本文在植物模拟方面的主要工作与贡献如下:  提出一种基于物理模拟的叶子动态构型方法。该方法采用质点弹簧模型来表示叶子的物理结构,本文基于植物学和物理原理,在这里引入了双层结构模型表达叶子的力学结构,很好地模拟了不同种类植物叶子形状的多样性。通过分析叶子形状变化的原因,即在叶子枯萎过程中,叶肉和叶脉由于各自不同的组织结构,导致了收缩比例不同。从而在物理模拟中,建立关于叶子基本结构的双层质点-弹簧模型,并对上下两层的不同参数的合理设置,很好地表现了叶肉和叶脉的不同力学特性。 双层模型的相互作用,决定了叶子的最终变形方式和效果,由此可以得到非常接近真实树叶的各种叶子形态。  提出“完全老化空间”和“老化度”的概念,用来模拟变化过程中的植物表观。该概念的可以非常真实地展现叶子秋季在干枯、老化过程中多种纹理、表观属性的变化。在生成叶子纹理的过程中,有别于以往基于单一材质样本的表观合成技术,本文采集了大量不同叶子样本表面的双向反射分布函数BRDF和双向透射分布函数BTDF,最终从这些数据中得到叶子衰老过程在老化空间中的表达式和完全分布图。结合植物学知识和所得到的老化空间中表达式和分布图,可以很好地指导合成各个季节中不同衰老程度叶子的表观纹理,并能外插合成采样范围之外的叶子纹理样式。本文在生成多种不同种类和衰老程度的植物叶子的过程中验证了这种方法的有效性,得到大量非常接近真实树叶的各种叶子表观和纹理.  提出一种基于随机过程的方法,对一类特征相似的叶子进行模拟,产生大量特征相似但细节不同的叶子模型。这种方法主要是通过基于特征值提取的数学方法来,随机地生成大量几何细节上不同,但主体特征相似的叶子。具体算法主要由二维流型上的拉普拉斯算子特征函数来完成。通过这种方法,可以快速生成几何细节上略有区别的同类叶子模型,大大提高了模型生成和构造的速度,从而使得本文可以生成大量不同的植物叶子。 表观采集技术是为了更加真实地对物体进行绘制而产生的技术。近年来,表观采集技术和表达方法逐渐的成为真实感绘制研究的主要问题,并获得了很大发展,它在高度真实感复杂场景绘制、虚拟现实、科学计算可视化等诸多领域都具有重要应用价值。本文针对基于BRDF和BTDF表达的表观和采样技术及其在实验应用设备进行了研究,主要贡献包括:  提出一种物体表面表观采集设备及其数据采集、处理方法。设备包括:光源移动平台、线性光源、均匀白色面光源、图像采集相机和控制/数据接收单元;通过采集的反射图像序列和透射图像,并对数据进行处理得到物体的双向反射分布函数BRDF数据和双向透射分布函数BTDF数据。本文的方法和设备成本低廉且精度高,而且能够同时采集物体表面的双向反射分布函数BRDF和双向透射分布函数BTDF,具有采集速度快、数据密度大等特点。
英文摘要: Weathering of plants including appearance capturing is a hot topic in the research area of computer graphics, significant in both the academic research and practical application. Focusing on the topic, several research results are achieved in the thesis. Weathering of plants is very important for exhibiting the natural objects realistically, while it is still a challenging problem till now. Along with the progress in the study of plants, on modeling and rendering, the topic has been receiving more and more attention from researchers. People are making effort to improve the effects of plants in both geometry and appearance to meet the requirements from rendering applications. In the thesis, we focus on the study in geometry modeling and appearance synthesis of plant leaves. We put forward a number of techniques in leaf modeling, aging space and appearance synthesis to the plant leaves. These techniques would enhance the feasibility of realistic plant rendering, and have important practical values. The main contributions of our work include the following aspects:  We present a method for the efficient simulation of a large number of plant leaves, realistically showing their weathering process in autumn, with various deformed shapes. In modeling various shapes of leaves for weathering, we introduce a botanically and physically based method for simulating variations of leaf shapes by using a double layered model (DLM). This model takes advantage of the key observation that the withered shapes of leaves are caused by different shrinkages between the mesophyll cells and vein cells during the aging process of leaves. By setting up a mass-spring system in two interconnecting layers, different kinetic manners of mesophyll and veins can be simulated respectively. Meanwhile the double layers affect each other and determine together the deformed shape of leaves.  We present a method for efficient simulation of a large number of plant leaves, realistically showing their weathering process in autumn, with various texture patterns and appearances. In generating the texture patterns of leaves, deferring from the existing techniques in modeling the appearance manifolds from a single input material sample, we capture the BRDF and BTDF properties of leaf surface from multiple various samples, which can finally obtain a complete aging space representing the appearance change through the aging process of the leaves. In comparison with this aging space represention and botanical knowledge, we could synthesize the appearance and textures for variety of leave types, and at the same time could extrapolate texture patterns out of input samples. We demonstrate the effectiveness of the method in several applications, including analysis of leaf textures in subjects with different ages and types. In most cases, we are able to re-produce texture patterns consistent with those observed in nature.  We present an algorithm based on stochastic process to simulate a large group of leaves with same symbol but variety of details. In this algorithm, we use feature extraction method to extract the main characteristics of curled leaves and use stochastic mathematical tools to generate different details. Here we use Laplacain operator in 2D manifolds to get eigenfunction. By this algorithm, we could generate a large number of similar leaves with different details quickly. As a result, the performance of plant leaf modeling would be greatly improved. Appearance capturing technologies were originally put forward to give rendered scenes a more realistic optical representation. Recently, appearance capturing algorithm has become the mainstream of realistic rendering technologies and achieved great progress. Appearance capturing technologies also have important application values in many other fields, such as photo-realistic rendering, virtual reality and visualization in scientific computing. In this thesis, we have studied the process of BRDF and BTDF capturing and the corresponding capturing facilities. By an investigation to this topic, an algorithm for capturing the appearance of objects was proposed and a design of the capturing system was made. The componenets of the system include the light source moving gantry, linear light source, uniform back light, capturing camera, and control/data processing unit. By capturing images of the object in different lighting conditions and processing the captured images, we obtain the Bidirectional Reflection Distribution Funciton (BRDF) and Bidirectional Transmission Distribution Funciton (BTDF) of the captured object. Our system is easy to build up with low cost and the capturing is highly accurate, with high resolution of the data captured. Meanwhile the operation to the capturing system is pretty convenient and efficient.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.iscas.ac.cn/handle/311060/5676
Appears in Collections:计算机科学国家重点实验室 _学位论文

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Recommended Citation:
迟小羽. 植物老化过程模拟研究[D]. 软件研究所. 中国科学院软件研究所. 2009-02-06.
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