| 摘要: | 三角網格為三維模型中最常見的模型資料，且廣泛應用於各個領域上，尤其為現階段產品開發流程中最常使用的模型之一。而產品開發流程多整合正向、逆向工程與快速成型製造。然而以逆向工程而言，其流程包含有量測資料、幾何特徵與幾何模型三個步驟，這三個步驟中皆以三角網格模型作為媒介，如量測的資料多以網格模型來表達，幾何特徵中的特徵與分離亦是以網格模型為基礎，而最後的幾何模型重建同樣以特徵分離後的網格模型來進行曲面重建。另外就快速成型製造而言，仍然是以三角網格作為輸出的橋梁。所以依現階段產品開發流程中，三角網格的應用情形，將有關網格的處理與技術分為三個主軸，即為本研究所發展的各項技術且具體說明如下： (1) 網格錯誤偵錯與修正技術：將錯誤的網格情形分為5種，分別為退化網格、不合理網格邊、自交網格、不完全連接網格與網格法向量不一致。將錯誤網格的類型分類並予以判斷與修正。 (2) 發展網格二次曲面特徵辨識與分離技術：提出以網格頂點法向量與曲率值為基礎，辨識網格模型中的二次曲面特徵並與以分離。 (3) 發展網格局部特徵置換技術：使經過修改或變更過的特徵網格能夠迅速與原始網格替換，達到加速產品設計開發中的修改與確認流程。 Triangle mesh is a common geometric model and is widely used in the field of engineering, especially in the product development process which involves forward engineering, reverse engineering and rapid prototyping. In reverse engineering, for rxample, the measured data is always saved as triangle meshes. Feature segmentation and surface reconstruction are generally implemented on the base of triangle meshes. Moreover, the input data of a rapid prototyping process is still triangle meshes. In this study, three important problems on triangle meshes wre investigated and appropriate algorithms are developed to deal wth these problems. Specifically, the three problems addressed are as follows: (1) Repairing triangle meshes: it is an approach to detect and eliminate erroneous facets on triangle meshes. Five types of erroneous facets are identified, namely, degenerate, non-manifold vertices, self-intersection, incomplete connection and inconsistent plane normal. Algorithms for dealing with all these erroneous facets are developed. (2) Feature segmentation algorithms for quadratic surfaces: it is composed of two steps. First, a region growing is developed to search for a small area near a seed point to determine the feature type, which can be a plane, a spherical surface, a cylindrical surface or a conical surface. Second, a re-growing procedure is employed to search for the points of the same feature type. (3) Partial mesh replacement: it is composed of three steps: cutting path computation, mesh segmentation and mesh stitching. The cutting path computation is employed to evaluate the intersecting points of all meshes lying under the projection of the boundary curve. Mesh segmentation is employed to divide the original meshes into two parts: preserved and replaced meshes. Mesh stitching is finally employed to sew the boundaries of the preserved and new meshes. |
