利用位移貼圖表示幾何細節之網格表示法及其在形變網格的應用

Abstract

本計劃之目的在於發展一個利用位移貼圖的新網格表示方式, 利用簡化過之基底網格(base mesh) 來表示原始模型外觀, 並利用位移貼圖(displacement map)儲存該基底網格與原始模型之間的幾何誤 差。在顯像階段則透過可程式化繪圖硬體進行顯像。由於繪圖之對像為基底網格, 因此可大幅提高顯 像速度, 且位移貼圖可彌補模型簡化之幾何誤差, 使得成像品質接近於原始模型。為了實現此一架構, 我們將在網格簡化機制上加入額外的限制來達到位移貼圖之需求, 且提出新的簡化誤差評量方法來降 低基底網格可能產生之誤差。貼圖品質也是影響成像之重要關鍵, 因此我們也將提出新的階層式網格 架構下的參數化最佳化技術, 並將模型表面幾何訊號與使用者權重列入參數化考量。此外, 我們也將 克服目前利用繪圖硬體顯像位移貼圖之方法用於所提出之表示法架構的問題。我們將更進一步把所提 出之網格表示法應用於具有動作(animated)之模型上。在模型簡化階層考量物體動作以建立對動作最佳 化之基底網格, 並在執行階層修正位移貼圖可能產生之表面扭曲與穿刺現象。 本計劃為期三年。第一年之目標為建立該網格表示法的模型簡化架構, 並提出一新的簡化誤差評 量機制來進一步提升基底網格的品質, 且同時強化位移貼圖之即時顯像機制。第二年將針對適用於位 移貼圖的基底網格之簡化機制與參數化進行最佳化。在網格簡化上將以位移貼圖之品質最佳化為目標 發展網格簡化的機制。而參數化上將透過所提出之階層式網格參數化技術來建立合理的參數化。並針 對原始模型表面上之幾何訊號與使用者主觀之權重資訊進行參數化的加強。第三年將把所提出之表示 法延伸至處理具有動作之模型上。針對模型之動作進行基底網格之最佳化, 且提出方法以避免位移貼 圖在模型動態改變過程中可能對表面產生之扭曲與穿刺現象。

In this project, we will develop a new mesh representation in which the global shape of the mesh will be represented by a simplified base mesh and the geometry difference between the original mesh and the base mesh will be stored in a displacement map. Such representation method will enable the real time rendering of the given mesh using graphics hardware, and, in the meantime, achieve the realistic rendering by recovering the geometry details using displacement map. To derive the proposed representation for a given mesh, we will develop a simplification mechanism that takes into account the requirements for a valid displacement map and is supported by a new simplification error metric. Since the quality of the displacement map directly affects the quality of rendering, we will develop a new parameterization scheme based on texture adaptation and level-of-detail modeling. Moreover, signal of geometry deviation shall be taken into account in the parameterization, and user assisted parameterization will be considered to further improve the quality of displacement map. Finally, the real time rendering of the displacement mapping will be greatly enhanced or modified to meet the need of the proposed representation. We will also apply the proposed mesh representation to the animated models. In the simplification stage, we will take the animation sequences of the model into account and produce an optimal base mesh for the animated model. And during the run-time, the distortion and self penetration due to the displacement mapping will also be dealt with. This is a three-year project. In the first year, we will develop a simplification framework for constructing the proposed mesh representation. We will consider the constraints necessary for generating a valid displacement map and develop a new simplification error metric. Moreover, we will study how to extend current real time rendering of displacement map to account for the more complicated requirements for the proposed representation. In the second year, we will focus on how to improve the quality of the displacement map. Firstly, a new parameterization based on texture adaptation and LOD modeling will be proposed. Moreover, signal of geometry deviation will be included in the parameterization, and user-assisted parameterization will be attempted. Secondly, a new simplification scheme that fully aims to produce a well-parameterized displacement map will be studied. In the third year, we will extend the proposed representation to deal with the animated model. Simplification scheme will be adapted to the animated sequence and aims to generate a good base mesh. We will also try to remove the surface distortion and self penetration due to the displacement mapping for animated model.