【作者】 李颖；

【导师】 唐勇；

【作者基本信息】 燕山大学 ， 计算机应用技术， 2018， 博士

【摘要】 海洋是地球生命的摇篮,是人类赖以生存和发展的重要空间,虚拟海洋在科学研究、海洋工程、军事训练、旅游和文化传播等多个领域中应用广泛。研究者们一直致力于寻找真实可信、计算代价小的建模和绘制方法。本文针对虚拟海洋场景的四个重要组成部分:海浪绘制、海面细节模拟、海面综合光学效果渲染和海洋场景人机交互展开研究,旨在实现真实感、实时性和交互性三方面的平衡。首先,针对目前计算机图形学领域普遍采用典型长波海浪谱进行海浪建模导致短波效果缺失的问题,提出一种基于长短波统一方向谱的海浪实时绘制方法。在现有海浪谱对比分析基础上,借鉴海洋遥感领域的全方向谱,引入长短波统一方向谱并加以改进,使之涵盖风速、风向、风区和水深参数,并且各项参数可调可控,有效弥补现有方法在高频短波绘制效果上的不足。其次,针对海面漂浮物、交互波及漩涡等复杂海面细节实时模拟问题,引入体素化方法对海面漂浮物体进行体素划分,以体素为基本单位对物体进行受力分析和计算,基于物理的刚体动力学原理,真实再现包括凹多面体在内的任意形状物体在海面上的运动状态;基于体积守恒原理,将海洋表面交互波的生成和传播假设成两个独立过程,构建反映液体自由表面波性质的交互波生成公式,确定交互波生成位置和初始振幅值;提出带有粘性阻尼系数的二维波动方程,并引入Verlet积分法求解,实时模拟交互波的传播扩散过程;简化漩涡构造方法,巧妙地采用顶点扭曲方法在着色器中快速生成海洋场景中的漩涡效果。再次,为真实再现海洋表面动态和复杂的光学效果,提出一种时空驱动的海面综合光照渲染模型。采用天空球进行天空建模,基于简化的天文模型计算太阳和月亮的运动轨迹,增加天空的灵活性和真实感;分析晴朗天空特征,基于颜色渐变纹理和简化的散射方程实现大气散射效果的实时模拟;建立海面微面元BRDF光照模型,真实再现海面对太阳光和天空光的反射效果;构建海面次表面散射模型,引入双极点漫反射方法近似求解,真实反映海下光线传播对海面光学效果的影响。然后,针对当前虚拟海洋场景人机交互方式单一的问题,提出一种虚拟海洋场景体感交互扩展系统框架。引入深度摄像头作为体感交互设备,设计简单高效的手势语义集合,建立人体骨骼运动和虚拟海洋场景中各要素的对应关系,实现体感控制海浪、光照及战舰等海洋军事元素;引入粒子系统快速真实模拟战舰航行时的白浪尾迹;简化航母舰载机起飞流程,将战舰行进体感控制方式扩展至舰载机飞行控制方面;构建单用户和多用户团队/对战模式,提供给用户高自由度交互体验。最后,设计并实现多种验证、优化和评价实验,实验结果表明虚拟海洋场景的真实感、实时性和交互性得到有效的改善。更多还原

【Abstract】 The ocean is the cradle of life on the earth,and it is an important space for human survival and development.The virtual ocean is widely used in many fields such as scientific research,ocean engineering,military training,tourism and cultural communication.Researchers have been working to find models that are authentic and computationally inexpensive.We focus on four important components of virtual ocean scenes: wave rendering,surface detail simulation,surface optical effect rendering and human-computer interaction.Our aim is achieving a balance of realism,real time and interactivity.Firstly,long wave spectrums are frequently used to model ocean waves in the field of computer graphics,which cause the lack of short wave effects.We propose a real time rendering method based on a unified direction spectrum for long and short waves.Based on the comparison and analysis of existing wave spectrums,we learn from the omnidirectional spectrum in the field of ocean remote sensing,then we introduce and improve the unified direction spectrum for long and short waves.The improved spectrum covers the wind speed,wind direction,wind fetch and water depth parameters,and the parameters can be adjusted and controlled.The method effectively makes up for the shortcomings of the existing methods.Secondly,aiming at the real-time simulation of ocean surface details,we introduce the voxelization method to classify the objects floating on the ocean,and carry out the force analysis and calculation on the basis of voxels.Using the principle of physical rigid body dynamics,we reproduce the real motion states of arbitrarily shaped objects on the ocean surface including the concave polyhedron.Based on the principle of volume conservation,the generation and propagation of interactive waves are assumed to be two independent processes.We construct an interactive wave generation formula which determines the position and initial amplitude of the interactive wave.The formula also reflects the properties of liquid free surface waves.To simulate the propagation and diffusion process of interactive wave in real time,we put forward a two-dimensional wave equation with a viscous drag coefficient,and the Verlet integral method is introduced to solve the equation.We simplify the vortex construction method and skillfully use the vertex warping method to quickly generate vortex effects in ocean scenes using shaders.Thirdly,in order to reproduce the dynamic and complex optical effects of the ocean surface,we build up a comprehensive ocean lighting rendering model which is driven by time and space.In this model,we apply a skysphere method which is convenient to position the celestial objects and to set up the light scattering model.To show the real movement of celestial spheres,we establish a simplified astronomical model to compute the position of every single celestial sphere in the scene.Via analyzing the characteristics of the clear sky,we realize the atmospheric scattering effect based on the color gradient texture and the simplified scattering equation.We set up an ocean BRDF illumination model to compute the light reflected from the sun and the sky dome.Considering the light scattering in the ocean,we construct a subsurface scattering model of the ocean,and approximate the diffusion solution due to a dipole source method.Furthermore,aginst the monotony of human-computer interaction in virtual ocean scenes,we propose a somatosensory interactive expansion system for virtual ocean scenes.Introducing a depth camera as the somatosensory interaction device,we design a simple and efficient gesture semantics set,and establish the correspondence between human skeleton motion and various elements in the virtual ocean scene,which realize the somatosensory control of ocean elements such as waves,lights and warships.The white-wave trail of the warship is rapidly and realistically simulated by the using of particle systems.We simplify the take-off process of the carrier-based aircraft,and extend the warship’s traveling somatosensory control to the flying control of the carrier-based aircraft.In addition,we apply single-user and multi-user team/combat modes to provide interactive experiences with high degrees of freedom.Finally,we design and implement a variety of verification,optimization and evaluation experiments.The experimental results show that the realism,real time and interactivity of ocean scenes are effectively improved.更多还原