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Level of detail technique for plant models
Realistic modelling and interactive rendering of forestry and landscape is a challenge in computer graphics and virtual reality. Recent new developments in plant growth modelling and simulation lead to plant models faithful to botanical structure and development, not only representing the complex architecture of a real plant but also its functioning in interaction with its environment. Complex geometry and material of a large group of plants is a big burden even for high performances computers, and they often overwhelm the numerical calculation power and graphic rendering power. Thus, in order to accelerate the rendering speed of a group of plants, software techniques are often developed. In this paper, we focus on plant organs, i.e. leaves, flowers, fruits and inter-nodes. Our approach is a simplification process of all sparse organs at the same time, i. e. , Level of Detail (LOD) , and multi-resolution models for plants. We do explain here the principle and construction of plant simplification. They are used to construct LOD and multi-resolution models of sparse organs and branches of big trees. These approaches take benefit from basic knowledge of plant architecture, clustering tree organs according to biological structures. We illustrate the potential of our approach on several big virtual plants for geometrical compression or LOD model definition. Finally we prove the efficiency of the proposed LOD models for realistic rendering with a virtual scene composed by 184 mature trees.
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道路矢量简化的自动阈值算法研究
矢量数据的简化方法是地理信息系统中的重要方面.通过提取距离和角度两方面信息可以有效简化和压缩矢量数据.本文在距离和角度简化基础上,提出了自动阈值简化方法与LOD技术的融合,在保证矢量数据精度下,有效减少了数据量.本文的方法,可以在矢量数据与高程数据融合等多方面工程中得到应用.
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地形矢量信息的分块与LOD技术的研究与实现
矢量信息是地形建模当中非常重要的一类信息.作者研究了地形矢量信息分块与LOD的一些关键技术和实现方法,目的是为了正确地把矢量数据叠加到DEM上,并保证地形的渲染效率.作者以道路的矢量数据为例,研究了这两种技术的实现方法,并进行了多组试验,得到了满意的效果.
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LOD技术在三维骨骼体可视化中的应用
针对骨骼模型结构离散化特点,在一般边崩塌算法的基础上,提出了一种基于顶点对融合的模型简化算法.该算法不仅适用于连续的三维模型,而且适用于像骨骼一样的骨骼块之间不连续的三维模型.通过实际的脚骨骼模型简化,证明了该算法的有效性和实用性.
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晚发性抑郁症和轻度认知障碍及阿尔茨海默病的关联
晚发性抑郁症(late-onset depression,LOD)、轻度认知障碍(mild cognitive impairment,MCI)和阿尔茨海默病(Alzheimer disease,AD)在临床上联系紧密但关系尚不完全清楚.我们将从流行病学、病理生理机制、大脑认知储备等方面对此进行综述.
