油气地质建模综合技术研究进展

地质模型的三维可观化实现是油气勘探开发领域一个重要的技术环节。本文在综述三维地学可视化合技术的基础上，探讨了可视化实现过程中的三维地质格架模型建立、空间网格化方法、属性插值及计算机图形可视化关现技术等关键问题。并指出了地质模型三维可视化技术的发展趋势和研究思路。     

数学模型可视化研究与实现

计算机硬件图像处理功能的增强,促进了计算机图形学的发展,进而促进了计算机的可视化研究。数学模型的可视化就是将抽象的数学函数以图形的方式表示出来,使人们对其有一个直观的认识。卫星云图,医疗成像系统都是计算机可视化的实际应用。文章介绍了在VC++6.0开发环境下,利用OpenGL来实现数学模型的可视化。该可视化系统包括数学函数的输入、识别、二维图形的输出、由二维曲线旋转生成三维立体图形以及三维图形的变换输出。     

基于L系统的水稻根系建模与可视化

基于L系统研究水稻根系三维建模及可视化, 动态模拟水稻根系生长过程. 通过分析水稻根系结构及生长特性, 定义了水稻根系生长模型, 包括: (1)根尖、分枝、种子根发根节点和不定根发根节点模式字符串; (2)单根生长、单根分枝、产生种子根和不定根产生式; (3)产生种子根及不定根节点的公理. 通过不断迭代模拟水稻根系生长变化过程, 并利用L-studio实现水稻根系生长的三维可视化. 同时将重力因子G和偏转因子D加入水稻根系生长模型中, 考察上述两个因子作用下水稻根系的生长特性. 通过实验可知当G≈0.3, D≈0.3时, 水稻根系生长模拟结果比较符合实际情况, 可为其他植物根系生长模拟与可视化研究提供参考.     

基于3DMax技术的胡杨茎生长模拟

植物生长模拟研究,是利用计算机技术以可视化的形式描述植物的生长状态。本研究在综合国内外相关研究成果的基础上,以南疆胡杨茎为研究对象,通过对胡杨茎的生长因子及结构形态的研究,提出一种基于三维结构的胡杨茎生长模型,并运用3DMax技术建模,实现胡杨茎的生长形态的可视化。本研究能促进人们对胡杨生长过程的理解和感知,为分析胡杨结构功能关系、调控生长模式等提供重要参考。     

三维云的建模和绘制

本文对计算机图形学中三维云的建模和绘制技术进行了概述,主要介绍目前比较典型的基于个体生长的云建模技术和基于物理过程的云建模技术.对基于个体生长技术中比较成功的粒子系统模型、变形球模型、体元模型、过程纹理函数模型进行详细分析,并总结了它们的成果与不足,比较了它们的适用范围,为研究三维云可视化技术提供借鉴.     

利用OpenGL实现内插算法可视化

OpenGL是一种交互式计算机图形系统,具有绘制三维图形的功能,能高效地编写出可操纵图形硬件的程序,支持三维可视化的实现。本文以OpenGL为基础,对可视化技术进行研究,重点讨论了内插算法,结合OpenGL中视点的定义,通过OpenGL的函数来实现。     

基于OpenGL的球体生成算法可视化仿真研究

研究计算机图像的三维可视化优化问题,针对图像生成慢的缺点,为了仿真计算机图形学中三维球体的生成过程,提高图像生成速度,提出了一种三角形分割的算法,实现了球体生成算法可视化的仿真系统CM.系统的实现,摒弃了原来可视化系统中依靠计算最佳逼近"像素点"的位置来显示图形的方法,而是用三角形面代替原来的"像素点",对其进行一系列的分割以实现最终效果.实验结果表明,方法可以实现三维图形生成算法可视化仿真效果,突破了原来只能实现二维图形的局限性,而且生成图形的速度较快,具有很好的逼真度.     

Reineke密度指数在日本落叶松林分自然稀疏模型研究中的应用

在日本落叶松林分生长模型研究的基础上,用Reineke定义的密度指数模拟了日本落叶松同龄林的自然稀疏模型和日本落叶松不同初植密度的自然生长过程表,这为日本落叶松人工林的密度管理提供了有力工具。     

OSG引擎在Android Studio中的移植和运行

基于OSG(Open Scene Graph)设计并实现一个在Android Studio平台三维场景的展示系统。分析OSG引擎和Android Studio平台的优势,以三维飞机场景为模拟案例,重点对Android Studio平台上建立可视化三维模型的步骤和构建三维模型的关键技术进行研究。结果表明,基于OSG的三维飞机模型应用在Android Studio平台上运行流畅,响应速度快,图形质量高,具有很好的交互性,为OSG在移动平台的整体移植提供了实践参考。     

基于三维模型转换器的虚拟植物可视化

提出了一个基于三维器官模型转换器来实现虚拟植物生长可视化的方法。该转换器的主要功能是在虚拟植物生长可视化系统内导入由三维建模软件所构造的具有表面细节的植物器官模型,之后结合L系统,实现由植物生长规律指导下的虚拟植物生长过程的实时模拟。实验结果表明,该方法改善了原有的一些虚拟植物生长可视化系统只考虑对器官进行几何建模,而忽略器官表面细节导致的展现效果真实感显著差异的缺陷。     

基于描绘单幅图像的三维树木交互建模系统

为了提高树木建模的真实感与可交互性,提出了一种基于单幅树木图像或直接手绘的交互式植物建模系统。系统根据植物形态学规律构建了标准三维树木的模板。通过描绘图像中树的主要枝干,结合叶序周规律,基于三维模板树将其从二维图像变换到三维模型,并通过弯曲、增加和删除枝干以及添加树叶等交互式操作生成和修改三维树木模型。实验结果表明,该系统能便捷快速地生成真实感较强的三维树木。     

个性化编辑的轻量化3维树木模型构建

目的 3维树木几何结构和拓扑结构的复杂性,不仅使得真实感3维树木模型的构建过程十分复杂,而且构建的模型文件包含大量的几何数据。针对3维树木模型的构建过程复杂和模型数据量大的问题,提出一种支持骨架个性化编辑的轻量化3维树木模型构建方法。方法 该方法在提取树木模型骨架结构的基础上,通过交互方式对3维树木模型的骨架进行个性化编辑以生成3维树木模型的全新骨架结构,并采用枝干和树冠模型的简化方法实现轻量化3维树木模型的构建。结果 该方法不仅能快速创建轻量化的3维树木模型,减少3维树木可视化时的模型绘制时间;而且能通过骨架个性化编辑来设计树木的拓扑结构,有助于增加同一品种树木外部表现形态的多样性。结论 通过应用表明,本文轻量化3维树木模型构建方法不仅可以构建具有不同表现形态的3维树木模型,而且简化后的3维树木模型可以在无线网络、移动终端等资源有限情况下进行3维树木可视化。     

Printable 3D Trees

With the growing popularity of 3D printing, different shape classes such as fibers and hair have been shown, driving research toward class‐specific solutions. Among them, 3D trees are an important class, consisting of unique structures, characteristics and botanical features. Nevertheless, trees are an especially challenging case for 3D manufacturing. They typically consist of non‐volumetric patch leaves, an extreme amount of small detail often below printable resolution and are often physically weak to be self‐sustainable. We introduce a novel 3D tree printability method which optimizes trees through a set of geometry modifications for manufacturing purposes. Our key idea is to formulate tree modifications as a minimal constrained set which accounts for the visual appearance of the model and its structural soundness. To handle non‐printable fine details, our method modifies the tree shape by gradually abstracting details of visible parts while reducing details of non‐visible parts. To guarantee structural soundness and to increase strength and stability, our algorithm incorporates a physical analysis and adjusts the tree topology and geometry accordingly while adhering to allometric rules. Our results show a variety of tree species with different complexity that are physically sound and correctly printed within reasonable time. The printed trees are correct in terms of their allometry and of high visual quality, which makes them suitable for various applications in the realm of outdoor design, modeling and manufacturing.     

Three-dimensional surface reconstruction of tree canopy from lidar point clouds using a region-based level set method

In this article, a novel method is proposed for three-dimensional (3D) canopy surface reconstruction of trees using a region-based level set method. Both individual tree crowns and clusters of trees are first marked for further exploration. Multiple horizontal slices corresponding to different heights are obtained. The 3D structure of tree canopy is built using raw data from lidar point clouds. Also, new applications are proposed based on the new method for 3D forest reconstruction. The biomass parameters of the forest, including tree intersection area, tree equivalent crown radius, and canopy volume, can be calculated from stacking 2D slices of trees. Tree types are also identified and classified. The results indicate that this approach is effective for 3D surface reconstruction of forests including individual trees and clusters of trees, and that critical forest parameters (such as tree intersection area, tree position, and canopy volume) can be derived for the evaluation and measurement of biophysical parameters of forests.     

Non-linear matrix modeling of forest growth with permanent plot data: The case of uneven-aged Douglas-fir stands

Uneven‐aged forest management is acquiring increasing importance throughout the world as an alternative to clear cutting. Simple stage‐structured matrix models can be used to predict the growth of uneven‐aged stands, and they are easily incorporated in optimization analysis. Parameters of these models can be estimated from readily available permanent plot data. Such a growth and yield model is presented for mixed, uneven‐aged Douglas‐fir and hardwood stands. The model was calibrated with data from 66 permanent plots in Oregon and Washington. The density‐dependent matrix model predicts the number of trees by diameter class and species type, softwood or hardwood. The parameters are based on individual tree growth equations, individual tree mortality equations, and stand ingrowth equations. The individual tree equations are a function of tree diameter, stand density, species, and site index. The stand‐level ingrowth equations are a function of stand density. The model was validated in the short term by comparing the number of trees in each diameter and species class at the time of the second inventory with the number predicted by the model, given conditions at the first inventory. A long‐term validation of the model was also done by comparing the steady‐state stand structure and stand volume with those observed for old‐growth stands. The model was applied to show the effects of different cutting cycles on productivity, diversity of tree species and size, and financial returns. The results suggest that uneven‐aged management of the Douglas‐fir forest type in the Pacific Northwest can be as productive as even‐aged management, with the added benefits of continuous cover forestry.     

树木结构层次细化的立体树木图像构建

目的 2维转3维技术可以将现有的丰富2维图像资源快速有效地转为立体图像,但是现有方法只能对树木的整体进行深度估计,所生成的图像无法表现出树木的立体结构。为此,提出一种树木结构层次细化的立体树木图像构建方法。方法 首先利用Lab颜色模型下的像素色差区别将2维树木图像的树干区域和树冠区域分割开来,并对树冠区域进行再分割;然后,在深度梯度假设思想基础上建立多种类型的深度模板,结合深度模板和树冠的区域信息为典型树木对象构建初始深度图,并通过基础深度梯度图组合的方式为非典型树木进行个性化深度构建;最后,根据应用场景对树木深度信息进行自适应调整与优化,将树木图像合成到背景图像中,并构建立体图像。结果 对5组不同的树木图像及背景图像进行了立体树木图像的构建与合成。结果表明,不同形态的树木图像都能生成具有层次感的深度图并自适应地合成到立体背景图像中,构建树木图像深度图的时间与原始树木图像的尺寸成正比,而构建立体树木图像并合成到背景中所需时间在24 s之间。对立体图像质量的主观评价测试中,这些图像的评分均达到良好级别以上,部分立体图像达到了优秀级别。结论 该方法充分利用了树木的形态结构特征,能同时适用于典型和非典型树木,所构建的立体树木图像质量较高,具有丰富的层次感,并具有舒适的立体观看效果。     

Statistical Modeling of the 3D Geometry and Topology of Botanical Trees

We propose a framework for statistical modeling of the 3D geometry and topology of botanical trees. We treat botanical trees as points in a tree‐shape space equipped with a proper metric that captures the geometric and the topological differences between trees. Geodesics in the tree‐shape space correspond to the optimal sequence of deformations, i.e. bending, stretching, and topological changes, which align one tree onto another. In this way, the 3D tree modeling and synthesis problem becomes a problem of exploring the tree‐shape space either in a controlled fashion, using statistical regression, or randomly by sampling from probability distributions fitted to populations in the tree‐shape space. We show how to use this framework for (1) computing statistical summaries, e.g. the mean and modes of variations, of a population of botanical trees, (2) synthesizing random instances of botanical trees from probability distributions fitted to a population of botanical trees, and (3) modeling, interactively, 3D botanical trees using a simple sketching interface. The approach is fast and only requires as input 3D botanical tree models with a known upright orientation.     

基于三维分枝模型的树木模拟

虚拟自然场景的实时生成一直是图形学研究领域中一个富有挑战性的难题,作为自然场景的重要组成部分,树木的模拟也得到了广泛的重视.本文在实际建模中以三维分枝模型为基础,与随机繁衍L系统相结合,对树木模型进行了一些改进.将光源和重力的影响加入枝段的模型中,使生成树木的形态更加逼真;改进了分枝模式,使得生成树木的随机性得到加强;在绘制时根据不同距离选择不同复杂度的树木模型,加快了渲染的速度.