Retaining Engineering Feature on Deforming Subdivision Surface

• Other Authors: Tsoi, Yiu Wai (author.)
• Format: Others
• Language: English; Chinese
• Published: 2016
• Online Access: http://repository.lib.cuhk.edu.hk/en/item/cuhk-1292321

本論文提出方法在變形細分曲面上保持工程特點於的大小，形狀和功能。現有的計算機輔助設計軟件普遍用非均勻有理B樣條曲面作圖形表達方式，因為非均勻有理B樣條曲面能準確表示工程特點的大小。但是非均勻有理B樣條曲面不容易表達自由曲面。相對之下，細分曲面能在任意拓撲結構產生平滑表面，有效表達自由曲面。所以本文提出以細分曲面作圖形表達方式，方便設計師做出自由曲面的設計。本文提出的方案讓設計師改變現有的工程圖專案成為一個有自由曲面的設計，能同時保留原有的工程特點形狀和大小。 === 本文提出的方案先把現有的工程模型重新網格化，以減少細分曲面在奇點上的不理想變形。然後，我們透過一個高效率的重複局部/全局優化方法去回復原有的程特點在變成理想外形的工程模型。設計師可以省略重新手動建模的程序。原有的設計模型能有一個新的外型設計，成為一個更吸引的產品，同時，原有的工程特點可以保留在新的設計上，原有的工程特點功能得以保留，舊有的工程配件可以重用在新的設計上。 === A method is proposed for retaining the size and shape of engineering feature on a deforming subdivision surface. An effective alternating local/global optimization method with projections is used to retain features. The multi-resolution property and the ability to generate smooth surface from arbitrary topology of subdivision surface allows user to model freeform objects. The multi-resolution editing of subdivision surface is especially useful for obtaining a smooth mesh by editing a low-complexity mesh. Constrained deformation is applied to the low complexity mesh. This speed up the computation involved, and allows the constrained deformation of complex mesh to be performed in a real-time. The method proposed illustrates that constrained deformation can be applied to multi-resolution model constructed with subdivision surface such that essential functional features can be retained in a shape editing process. === Retaining features while modifying regular objects to freeform objects is always a challenging problem for existing engineering Computer-Aided Design (CAD) software. Most of the CAD softwares use CSG-tree and NURBS surface representation, which is effective in modeling regular engineering objects and is accurate in describing the dimension of features. However, CSG tree is inefficient in representing freeform objects. NURBS surfaces are essentially four-sided, which limits users to model shapes with general topology. === Subdivision surface is a better candidate than NURBS when it comes to representing freeform objects. It is capable of generating smooth surface with irregular topology, allowing user to model freeform object efficiently. However, the extraordinary vertices cause instability on the subdivision surface. The triangular mesh generated by CAD software always contains many extraordinary vertices, which is undesirable to be used as the base mesh of subdivision surface. === In the proposed method, we perform remeshing on the triangular mesh generated by CAD software to reduce the number of extraordinary vertices. We adopt incremental remeshing to locally regularize the mesh valence near feature vertices. The skinny triangles are removed by a global relaxation process using the local/global optimization framework. After remeshing, user can edit the coarse base mesh to the desired shape and propagate to the fine mesh, saving time and complexity of mesh editing. A local/global optimization scheme is used to solve the constrained deformation problem in order to retain both the shape and size of the user-selected engineering feature in a deformation. Given the mesh of a regular object, our method can facilitate user in redesigning the shape of an object to make it more attractive. At the same time, engineering features can be maintained, saving time and effort to rebuild the engineering features or redesign the component to fit in the deformed shape. === Tsoi, Yiu Wai. === Thesis M.Phil. Chinese University of Hong Kong 2016. === Includes bibliographical references (leaves ). === Abstracts also in Chinese. === Title from PDF title page (viewed on …). === Detailed summary in vernacular field only. === Detailed summary in vernacular field only.