We use cookies to improve your experience with our site.

梯度域网格变形技术综述

Gradient Domain Mesh Deformation - A Survey

  • 摘要: 1.本文的创新点梯度域网格变形技术是目前国际上网格变形领域的研究热点。通过将三维网格表示在梯度域中,梯度域网格变形技术能够很好地在大尺度变形中保持网格原有的细节特征,得到高质量的变形结果。本文对梯度域网格变形技术进行了深入的研究,并基于求解方式将梯度域变形技术分为两大类:线性化方法和非线性优化方法。本文对这两种方法都进行了深入探讨,并对其优缺点进行了详尽分析,期望能够帮助研究者迅速地了解和掌握这一当前热门的网格变形技术。
    2.实现方法梯度域网格变形技术以泊松方程为其理论基础,其变形算法的特点是将用户输入转化为对网格上梯度向量场的操作,并通过泊松方程重建变形过后的网格。由于梯度向量场有效地表达了原始网格的细节特征,因此,重建的变形网格能够很好的保持原有的细节特征。梯度域网格变形技术中的一个关键性技术问题是如何计算目标梯度向量场以得到高质量的变形结果。根据对这一问题求解方式的不同,本文将梯度域变形技术分为两大类:线性化方法和非线性化优化方法。 线性化方法的特点是要求用户在界面上输入旋转以估计目标向量场,从而通过泊松方程得到变形过后的网格。其代表方法有:测地线插值法,调和映射插值法,基于刚体变换下不变量的显式计算法,以及相似变换线性化法。这些方法的特点是实现较为简单,且能够在旋转不大的情况下得到较为满意的变形结果。本文对线性化方法及其衍生算法做了详细描述。 非线性优化方法则期望通过迭代直接得到目标向量场。它不要求用户在界面上输入旋转,并且理论上能够保证得到最优的变形结果。 此外,非线性优化方法还可以实现各种非线性约束,例如:骨骼约束,体积约束等。其代表方法有:非精确高斯牛顿迭代法,对偶拉普拉斯坐标法,以及基于变形句柄的简化模型法。除了对上述方法进行了详细描述以外,本文还对非线性优化方法在变形传递技术(Deformation Transfer)和空间变形技术中的应用进行了介绍。
    3.结论及未来待解决的问题梯度域网格变形技术中的线性化方法较非线性优化方法简单,易于实现,且速度上具有优势,但是产生的变形结果非最优结果。非线性化优化方法理论上可以保证最优结果,并且可以实现各种变形中需要的约束,例如:骨骼约束,体积约束等。但是其实现复杂,且速度较线性方法慢。用户可以根据具体应用选择变形算法。对结果要求较高且变形尺度大可选用非线性优化方法。如果追求速度,则可选用线性化方法。梯度域网格变形技术将来发展的一个可能方向是应用非线性优化方法去解决复杂模型的变形问题,例如非流形网格的变形,或者具有很多独立部件的三维模型的变形。

     

    Abstract: This survey reviews the recent development of gradient domain mesh deformation method. Different to other deformation methods, the gradient domain deformation method is a surface-based, variational optimization method. It directly encodes the geometric details in differential coordinates, which are also called Laplacian coordinates in literature. By preserving the Laplacian coordinates, the mesh details can be well preserved during deformation. Due to the locality of the Laplacian coordinates, the variational optimization problem can be casted into a sparse linear system. Fast sparse linear solver can be adopted to generate deformation result interactively, or even in real-time. The nonlinear nature of gradient domain mesh deformation leads to the development of two categories of deformation methods: linearization methods and nonlinear optimization methods. Basically, the linearization methods only need to solve the linear least-squares system once. They are fast, easy to understand and control, while the deformation result might be suboptimal. Nonlinear optimization methods can reach optimal solution of deformation energy function by iterative updating. Since the computation of nonlinear methods is expensive, reduced deformable models should be adopted to achieve interactive performance. The nonlinear optimization methods avoid the user burden to input transformation at deformation handles, and they can be extended to incorporate various nonlinear constraints, like volume constraint, skeleton constraint, and so on. We review representative methods and related approaches of each category comparatively and hope to help the user understand the motivation behind the algorithms. Finally, we discuss the relation between physical simulation and gradient domain mesh deformation to reveal why it can achieve physically plausible deformation result.

     

/

返回文章
返回