Surface Fairing and Surface Compression for 3D Ship Modeling

点击翻译按钮获取中文摘要

The purposes of this research are the development of an automatic surface fairing method for 3D ship-hull design and the development of a surface compression method for exchanging 3D data. The results of them are described as follows :1. Surface FairingSurfaces generated by conventional fairing methods often have unwanted features such as local perturbations and global waves. This research developed a new fairing method that avoids these features. The method consists of the following three steps. (1) Rearranging control points of lines-curves so that the weighted sum of their arc lengths and curvatures are equally distributed. (2) Rearranging control points along lines-curves by applying low-pass filters repeatedly. (3) For eliminating the local perturbations, an energy minimization technique for thin-plates is used by regarding each surface as a thin-plate. Our method was applied to examples of hull-form surfaces, and could effectively remove the both of global waves and local perturbations with limited changes of the shape.2. Surface CompressionSurface compression is effective for storing and distributing 3D CAD data, but existing compression methods failed to maintain the smoothness at surface boundaries. In our method, a NURBS surface is encoded using its boundaries and additional data. At first, an interpolating surface is calculated using the boundary curves of the original surface. Then, the differences between the original surface and the interpolating one are calculated. Difference data are optionally used, and they are represented in two types : distances only, and distances and orientations. One type is selected according to the tolerances of each surface. Finally, the boundary curves and the difference data are compressed using the discrete cosine trans-form (DCT). The results show our method can easily control the trade-off between the compression ratio and accuracy, and achieve a good compression rates. (291 words)