Abstract
多媒體技術對網際網路之應用日趨重要，但因受限於目前網路之頻寬，許多應用仍然無法令人滿意。尤其是關於圖形､影像､聲訊與視訊等之應用因其資料量均相當龐大，在網路上須耗費較長的通訊時間，而讓使用者無法忍受等待之苦。為了解決這類問題，影像､視訊及聲訊均有了國際之壓縮標準，如JPEG及MPEG等。但目前關於三維物體的壓縮不但尚無標準，且其相關的研究亦尚在起步階段。本論文主要的目的在研究幾何壓縮技巧，並提□□效的演算法；然後再根據此方法實際製作成壓縮及解壓縮的系統軟體。有關本壓縮及解壓系統之實際測試結果及討論亦詳述於本論文之中從測試之資料結果顯示，我們所建構的幾何壓縮系統不但能有效地加壓､解壓，而且其壓縮率十分良好。此外，我們利用虛擬實境中多精度 (Level of Detail ) 模型的概念，配合幾何壓縮的技巧，提出三維物件在Web上的漸進式顯像( Progressive display )之方法，並將此方法實作的子系統與幾何壓縮系統整合，以利於網路上之傳輸。最後，我們參考目前三維物體檔案壓縮之規格，訂定出一組 VRML v1.0之壓縮規格。經實例測試，我們的壓縮規格不但適用於VRML 的檔案，而且十分方便於壓縮與解壓縮之製作。Recently, the booming of multimedia applications in the Webspace has drawn great attention in the world of the informationtechnology. However, many multimedia applications are notsatisfactory due to the limitation of bandwidth of currentnetworks. To cope with this problem, compression techniques andstandards such as JPEG and MPEG have been developed in the mediasuch as image and video respectively. Unfortunately, there is nointernational compression standard for 3D geometry objects to betransmitted the networks. Even the published results ongeometry compression are few. In this thesis, we study thegeometry compression techniques and their correspondingcompression algorithms. Then according to our studies, acompression software system is implemented. Several testingmodels show that our system can encode and decode the geometrydata efficiently and effectively. Moreover, the notion of Levelof Detail (LOD) is incorporated in our compression modules toprovide the progressive display function of geetry objects inthe Web. Finally, referring to current geometry compressionspecifications, we propose a compression specification for VRMLv1.0. Empirical tests show that our compression format is notonly feasible but also sufficient in both encoding and decoding.