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点切向曲线曲面细分

Point-tangent Subdivision Curves and Surfaces

  • 摘要: 为了通过对控制顶点和控制顶点处单位控制切向量的细分实现光滑曲线和曲面的造型, 提出一种将传统线性细分格式推广到非线性细分格式的算法. 在每次细分步骤中, 首先线性细分顶点, 然后线性细分单位控制切向量并归一化得到单位切向量; 最后在得到的线性细分顶点处构造以单位切向量为法向的法平面, 将原顶点通过圆弧插值投影到法平面上, 再将法平面上的投影点加权平均得到新的细分顶点. 点切向的细分格式具有保圆和保圆柱面性质, 也与对应线性细分格式有相同的收敛性与光滑阶. 实例结果表明, 点切向细分格式适合于复杂的光滑空间曲线设计以及管状曲面的建模.

     

    Abstract: To achieve smooth curve and surface modeling through subdivision of control vertices and the unit control tangent vectors at the control vertices, an algorithm is proposed that extends the traditional linear subdivision scheme to a nonlinear subdivision scheme. In each subdivision step, the algorithm first linearly subdivides the vertices, then linearly subdivides the unit control tangent vectors followed by a normalization step to obtain unit tangent vectors. Subsequently, a normal plane is constructed at each linearly subdivided vertex using the obtained unit tangent vector as plane normal, and the original vertices are projected onto the normal plane by arc interpolation. Finally, the new subdivision vertices are obtained by weighted averages of the projection points on the normal planes. The nonlinear subdivision schemes based on point tangents can preserve circles and circular cylinders, and they have the same convergence and smoothness orders as linear subdivision schemes. The experimental examples show that the point-tangent subdivision schemes are beneficial for the construction of complex smooth spatial curves and the modeling of pipe-like surfaces.

     

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