Efficient and detailed sketch-based character modelling with composite generalized elliptic curves and ODE surface creators.

Abstract

Sketch-based modelling (SBM), dating back to 1980s, has attracted a lot of researches’ attention due to its easy-to-use features and high efficiency in generating 3D models. However, existing sketch-based modelling approaches are incapable in creating detailed and realistic 3D character models. This project aims to propose new techniques which can create more detailed 3D character models with easiness and efficiency. The basic idea is to fit primitives to the sketches consisting of front view contours, side view contours and cross-section curves to obtain more detailed shape, propose ODE (ordinary differential equation) driven deformation to create more realistic shapes, and use surfaces defined by cross-sectional curves to represent sketch-based and ODE-driven 3D character models. In order to achieve the above aim, this thesis firstly investigates curve fitting of cross-sectional shapes and solved the problem of representing cross-sectional curves with generalized ellipses or composite generalized elliptic segments. Then, this thesis proposes a new mathematical formula for defining a surface from the cross-sectional curves. A new sketch-guided and ODE-driven character modelling technique is proposed, consisting of two main components: primitive deformer and detail generator. With such a technique, I first draw 2D silhouette contours of a character model. Then, I select proper primitives and align them with the corresponding silhouette contours. After that, I develope a sketch-guided and ODE-driven primitive deformer. It uses ODE-based deformations to deform the cross-section curves of the primitive to exactly match the generated 2D silhouette contours in one view plane and with the curve-fitting method and surface re-construction method mentioned above, a base mesh of a character model consisting of deformed primitive is obtained. In order to add various 3D details, I develop a local shape generator which uses sketches in different view planes to define a local shape and employs ODE-driven deformations to create a local surface passing through all the sketches. The experimental results demonstrate that the proposed approach can create 3D character models with 3D details from 2D sketches easily, quickly and precisely. Cross-section contours are important in defining cross-section shapes and creating detailed models. In order to develop a cross-section contour- based modelling approach, how to mathematically represent cross-section curves must be first solved. The second aim of this project is to propose composite generalized elliptic curves and introduce them into character modelling to achieve an analytical and compact mathematical representation of cross-section contours. Current template-based character modelling which creates 3D character models from sketches retrieves and then uses 3D template models directly. Since retrieving 3D models from sketches is not an easy task, the third aim of this project is to extract 2D cross-section contours from template models and use the extracted 2D cross section contours as templates to assist the creation of 3D character models for simplifying and accelerating the modelling process. Although there are many different approaches to interpret shapes with sketch strokes, but to our knowledge, no one utilises 2D template cross-section contours to quickly generate the shapes of human characters in a sketch-based system, which is one of the contributions of this project.