Guoguang Du

Part-in-whole matching of rigid 3D shapes using geodesic disk spectrum

Part-in-whole matching of rigid 3D shapes has attracted great interest in shape analysis and has various applications in computational archaeology. Rigid part-in-whole matching algorithms are mainly based on methods minimizing geometric distances and methods using local shape descriptors, which are challenging when the partial shapes are relatively small and smooth. This paper proposes a part-in-whole matching algorithm of rigid 3D shapes using geodesic disk spectrum (GDS), which achieves accurate matching results for partial shapes with arbitrary boundaries or smooth appearances. The largest enclosing geodesic disk of the partial shape and geodesic disks on the complete shape are extracted in the matching process. GDS is used as the matching descriptor, which is the distribution of shape index for enclosing points of the disk. The problem of matching partial surfaces with arbitrarily irregular boundaries to the complete shape is transformed into the matching of geodesic disks with the same radius using the proposed algorithm. GDS is discriminative, which can handle the situation when partial surfaces have few distinctive features. The proposed algorithm has been tested on various partial surfaces and obtained accurate matching results. A higher precision is achieved by comparing with existing part-in-whole matching algorithms, which proves the efficiency of the proposed algorithm.

3D scanning modeling method application in ancient city reconstruction

With the development of optical engineering technology, the precision of 3D scanning equipment becomes higher, and its role in 3D modeling is getting more distinctive. This paper proposed a 3D scanning modeling method that has been successfully applied in Chinese ancient city reconstruction. On one hand, for the existing architectures, an improved algorithm based on multiple scanning is adopted. Firstly, two pieces of scanning data were rough rigid registered using spherical displacers and vertex clustering method. Secondly, a global weighted ICP (iterative closest points) method is used to achieve a fine rigid registration. On the other hand, for the buildings which have already disappeared, an exemplar-driven algorithm for rapid modeling was proposed. Based on the 3D scanning technology and the historical data, a system approach was proposed for 3D modeling and virtual display of ancient city.

An automatic positioning algorithm for archaeological fragments

One of the main challenges on digital preservation of cultural heritage is to reassemble broken fragments. However, large amounts of fragments are mixed randomly when discovered, which brings terrific difficulties for their reassembly. This paper introduces an automatic approach for positioning large mixed archaeological fragments which come from a particular kind of artifact. The main idea is to position fragments based on partial matching between fragments and a complete artifact model using the multi-scale, informative and robust Heat Kernel Signature. The positioning pipeline contains four steps: feature points extraction for fragments and the complete artifact model based on Heat Kernel Signature; initial matching between feature points by comparing their Heat Kernel Signature curves; wrong matches removing using a basis points driven refinement procedure and rigid transformation generating by selecting three pairs of points among the correct matching results using farthest points sampling. After these steps, archaeological fragments can be positioned to different positions compared with the template model, which provides not only the classification information, but also the accurate relative position. The main contributions of this paper are using a novel feature extraction algorithm based on Heat Kernel Signature to assist partial matching, and a basis points driven refinement procedure to remove wrong matches. The proposed algorithm has been tested on the Terracotta Warriors fragments, and the results prove the effectiveness of the proposed positioning algorithm.

Classification and reassembly of archaeological fragments

Large number of archaeological fragments are mixed up when they are excavated, which brings difficulties for their reassembly. Computer aided restoration technologies have developed greatly in recent years, and approaches nowadays assist experts in a large scale. However, there still exist large number of fragments which are not reassembled and repaired. The current approaches have some disadvantages which affect the reassembly in large scale. This is because of the particular characteristics of archaeological fragments which affect the effectiveness of the current approaches. On the one hand, the archaeological fragments are piled up when they are excavated in archaeological sites. On the other hand, the fragments are changed during the long time because of abrasion and erosion. Therefore, innovative methods for the classification and reassembly of archaeological fragments are needed urgently. In this paper, the relate work on the classification and reassembly of archaeological fragments are first presented. Then, the problems when applying current approaches are summarized. At last, a feasible plan is given in order to classify and reassemble the fragments efficiently. By intact surface segmentation and partial matching with a complete model using discriminative feature descriptors, large number of fragments can be positioned with respect to a template model. The matching results provide the classification information and can assist the reassembly of fragments.

A Rapid Modeling Method for 3D Architectural Scene

The existing 3D scene layout methods, which mainly focus on indoor scenes, are limited in outdoor applications. In this paper, the example-based modeling method is introduced into the outdoor modeling, and an automatic layout optimization method for outdoor scenes is proposed. As an application platform, the sketch-based 3D model retrieval and assemble system is realized as well. Different from the current methods, firstly, we adopt an improved manifold sorting algorithm in sketch retrieval method, which can get the 3D models rapidly; secondly, according to particular properties of outdoor architectures, specialized energy constraints are proposed, which defines the energy function that meets the functional and aesthetic needs; thirdly, the scene achieves automatic layout by adopting simulated annealing algorithm. By stepped asymptotic optimization strategy and random jumps, we can avoid falling into constraint conflicts and local optimal traps. Experimental results show the robustness and effectiveness of our algorithm in different scenes. Our algorithm has been applied in the actual development of game scenes.

Classifying fragments of terracotta warriors using template-based partial matching

Large numbers of Terracotta Warriors fragments are mixed up when they are excavated, which calls the need for classifying them in order to avoid one to all matches and improve the efficiency of reassembly. In this paper, we propose a novel template-based classification algorithm for Terracotta Warriors fragments, which transforms the problem of classification into the problem of partial shape matching. Firstly, a few distinct regions, which indicate categories of the fragments, are selected as templates from collections of fragments. Secondly, a novel partial matching procedure is proposed to find whether a fragment have a sub-region that is similar to one of the templates. If there exists a sub-region on the fragment that is similar to one of the templates, this fragment is considered to belong to the category that the matching template represents. The partial matching procedure consists of a coarse matching and a fine matching, which utilizes the normal distribution descriptor and the modified point feature histogram descriptor, respectively. The normal distribution descriptor characterizes the structure of a Euclidean-sphere region and the modified point feature histogram descriptor characterizes the structure of a geodesic-disk region. Experiments have been conducted on Terracotta Warriors fragments that are scanned from real sites to verify the effectiveness of our method. Comparing with other partial matching methods, more accurate classification results are achieved.

Stable and realistic crack pattern generation using a cracking node method

This paper presents a method for simulating surface crack patterns appearing in ceramic glaze, glass, wood and mud. It uses a physically and heuristically combined method to model this type of crack pattern. A stress field is defined heuristically over the triangle mesh of an object. Then, a first-order quasi-static cracking node method (CNM) is used to model deformation. A novel combined stress and energy combined crack criterion is employed to address crack initiation and propagation separately according to physics. Meanwhile, a highest-stress-first rule is applied in crack initiation, and a breadth-first rule is applied in crack propagation. Finally, a local stress relaxation step is employed to evolve the stress field and avoid shattering artifacts. Other related issues are also discussed, such as the elimination of quadrature sub-cells, the prevention of parallel cracks and spurious crack procession. Using this method, a variety of crack patterns observed in the real world can be reproduced by changing a set of parameters. Consequently, our method is robust because the computational mesh is independent of dynamic cracks and has no sliver elements. We evaluate the realism of our results by comparing them with photographs of real-world examples. Further, we demonstrate the controllability of our method by varying different parameters.

Rapid three-dimensional scene modeling by sketch retrieval and auto-arrangement

A completed workflow for rapid 3D outdoor scene modeling is implemented.Sketch-based retrieval is improved by manifold ranking obtaining high accuracy.Energy function is composed by specific constraints designing for outdoor scenes.Auto-arrangement is optimized by PSO-SA algorithm efficiently.Effectiveness is proved by evaluations of practical experiments and user study. Display Omitted The existing three-dimensional (3D) object layout methods are focused mainly on indoor scenes and they are limited for outdoor applications. In this study, we propose a data-driven method for outdoor scene modeling by using fast retrieval and automatic optimization layout techniques. Unlike the current methods, we first employ an improved manifold ranking algorithm in the sketch-based 3D model retrieval stage, which achieves higher accuracy. Next, according to the particular properties of outdoor architectures, specialized constraints are then proposed to define an energy function, which meets both the functional and aesthetic requirements. Finally, we cast the auto-arrangement as a combinatorial optimization problem, which we solve using an optimization algorithm. In contrast to the earlier version of this method, which was presented at Cyberworlds 2016, this extended version combines simulated annealing and particle swarm optimization algorithms, which have the advantages of rapid convergence and avoiding becoming trapped by local minima. Our experimental results demonstrate that the proposed method is more intuitive and effective for modeling 3D scenes, and can be employed in the actual development of game scenes.

HKS-Based Feature Extraction for 3D Shape Partial Registration

Heat Kernel Signature (HKS) is an informative and multi-scale descriptor that has been widely used in shape analysis. However, current feature extraction methods based on HKS are highly affected by the time scale, which limits its performance. For the task of 3D shape partial registration, this paper proposes a feature extraction algorithm based on the overlapping diffusion time of the partial shape and the complete shape, which not only eliminates the impact of time scale but also obtains consistent and stable feature points. A registration pipeline is also put forward that guarantees the accuracy. Experiments have been conducted on various partial shapes, and the validity of the algorithm was verified. Compared with other partial registration methods based on HKS, the proposed algorithm achieved more accurate results.

A mesh-insensitive elastic model for simulation of solid bodies

FEM-based elasticity models are popular in solid body simulation. To avoid its problems of mesh sensitivity and overly stiff, a novel smoothed pseudo-linear elasticity model is presented. First, the smoothed finite element method is employed to alleviate mesh distortion and overly stiff problems instead of the traditional spatial adaptive smoothing method. Then, we propose a smoothing domain-based stiffness warping technique to compensate the nonlinear errors introduced by linear elasticity models. With this approach, transient displacements are slightly affected by mesh distortion and total volumes are preserved under large rotations. It also shows apparently softening effects in the experiments. Simulation results are generated without adding significant complexity or computational cost to the standard corotational FEM.