Apostolos Axenopoulos

A 3D Shape Retrieval Framework Supporting Multimodal Queries

This paper presents a unified framework for 3D shape retrieval. The method supports multimodal queries (2D images, sketches, 3D objects) by introducing a novel view-based approach able to handle the different types of multimedia data. More specifically, a set of 2D images (multi-views) are automatically generated from a 3D object, by taking views from uniformly distributed viewpoints. For each image, a set of 2D rotation-invariant shape descriptors is produced. The global shape similarity between two 3D models is achieved by applying a novel matching scheme, which effectively combines the information extracted from the multi-view representation. The experimental results prove that the proposed method demonstrates superior performance over other well-known state-of-the-art approaches.

3D model search and retrieval using the spherical trace transform

This paper presents a novel methodology for content-based search and retrieval of 3D objects. After proper positioning of the 3D objects using translation and scaling, a set of functionals is applied to the 3D model producing a new domain of concentric spheres. In this new domain, a new set of functionals is applied, resulting in a descriptor vector which is completely rotation invariant and thus suitable for 3D model matching. Further, weights are assigned to each descriptor, so as to significantly improve the retrieval results. Experiments on two different databases of 3D objects are performed so as to evaluate the proposed method in comparison with those most commonly cited in the literature. The experimental results show that the proposed method is superior in terms of precision versus recall and can be used for 3D model search and retrieval in a highly efficient manner.

Three-Dimensional Shape-Structure Comparison Method for Protein Classification

In this paper, a 3D shape-based approach is presented for the efficient search, retrieval, and classification of protein molecules. The method relies primarily on the geometric 3D structure of the proteins, which is produced from the corresponding PDB files and secondarily on their primary and secondary structure. After proper positioning of the 3D structures, in terms of translation and scaling, the spherical trace transform is applied to them so as to produce geometry-based descriptor vectors, which are completely rotation invariant and perfectly describe their 3D shape. Additionally, characteristic attributes of the primary and secondary structure of the protein molecules are extracted, forming attribute-based descriptor vectors. The descriptor vectors are weighted and an integrated descriptor vector is produced. Three classification methods are tested. A part of the FSSP/DALI database, which provides a structural classification of the proteins, is used as the ground truth in order to evaluate the classification accuracy of the proposed method. The experimental results show that the proposed method achieves more than 99 percent classification accuracy while remaining much simpler and faster than the DALI method

Real-Time Skeleton-Tracking-Based Human Action Recognition Using Kinect Data

In this paper, a real-time tracking-based approach to human action recognition is proposed. The method receives as input depth map data streams from a single kinect sensor. Initially, a skeleton-tracking algorithm is applied. Then, a new action representation is introduced, which is based on the calculation of spherical angles between selected joints and the respective angular velocities. For invariance incorporation, a pose estimation step is applied and all features are extracted according to a continuously updated torso-centered coordinate system; this is different from the usual practice of using common normalization operators. Additionally, the approach includes a motion energy-based methodology for applying horizontal symmetry. Finally, action recognition is realized using Hidden Markov Models (HMMs). Experimental results using the Huawei/3DLife 3D human reconstruction and action recognition Grand Challenge dataset demonstrate the efficiency of the proposed approach.

A Compact Multi-view Descriptor for 3D Object Retrieval

In this paper, a novel view-based approach for 3D object retrieval is introduced. A set of 2D images (multi-views) are automatically generated from a 3D object, by taking views from uniformly distributed viewpoints. For each image, a set of 2D rotation-invariant shape descriptors is extracted. The global shape similarity between two 3D models is achieved by applying a novel matching scheme, which effectively combines the information extracted from the multiview representation. The proposed approach can well serve as a unified framework, supporting multimodal queries (such as sketches, 2D images, 3D objects). The experimental results illustrate the superiority of the method over similar view-based approaches.

Combining Topological and Geometrical Features for Global and Partial 3-D Shape Retrieval

This paper presents a novel framework for 3-D object content-based search and retrieval, appropriate for both partial and global matching applications. The framework is based on a graph representation of a 3-D object which is enhanced by local geometric features. The 3-D object is decomposed into meaningful parts and an attributed graph is constructed based on the connectivity of the parts. Every 3-D part is approximated with a suitable superellipsoid and a novel 3-D shape descriptor, called a 3-D distance field descriptor, is computed and associated to the corresponding graph nodes. The matching process used is based on attributed graph matching algorithm appropriate for this application. The proposed method not only provides successful retrieval results in terms of geometric similarity but also is invariant to rotation, translation and scaling of an object as well as to the different poses of articulated objects. Finally, it can be effectively used for partial and global 3-D object retrieval.

3D Content-Based Search Based on 3D Krawtchouk Moments

In this paper a novel method for 3D content-based search and retrieval is proposed. Guided by the imperative need for a reliable 3D content based search tool and the very interesting results of research work done in the past on the performance of Krawtchouk moments and Krawtchouk moment invariants in image processing, Weighted 3D Krawtchouk moments are introduced for efficient 3D analysis which are suitable for content-based search and retrieval applications. The proposed method was tested on Princeton Shape Benchmark. Experiments have shown that the proposed method is superior in terms of precision-recall comparing with other well-known methods reported in the literature.

Multimedia search and retrieval using multimodal annotation propagation and indexing techniques

In this paper, a complete solution for search and retrieval of rich multimedia content over modern databases is presented. The framework proposed in this paper combines the advantages of multimodal search with those of annotation propagation into a unified system. Moreover, an effective technique, which is appropriate for large-scale indexing, is adopted, extended and integrated to the proposed framework so as to achieve optimized search and retrieval of rich media content even from large-scale databases.

Investigating the Effects of Multiple Factors Towards More Accurate 3-D Object Retrieval

This paper proposes a novel framework for 3-D object retrieval, taking into account most of the factors that may affect the retrieval performance. Initially, a novel 3-D model alignment method is introduced, which achieves accurate rotation estimation through the combination of two intuitive criteria, plane reflection symmetry and rectilinearity. After the pose normalization stage, a low-level descriptor extraction procedure follows, using three different types of descriptors, which have been proven to be effective. Then, a novel combination procedure of the above descriptors takes place, which achieves higher retrieval performance than each descriptor does separately. The paper provides also an in-depth study of the factors that can further improve the 3-D object retrieval accuracy. These include selection of the appropriate dissimilarity metric, feature selection/dimensionality reduction on the initial low-level descriptors, as well as manifold learning for re-ranking of the search results. Experiments performed on two 3-D model benchmark datasets confirm our assumption that future research in 3-D object retrieval should focus more on the efficient combination of low-level descriptors as well as on the selection of the best features and matching metrics, than on the investigation of the optimal 3-D object descriptor.

Search and Retrieval of Rich Media Objects Supporting Multiple Multimodal Queries

In this paper, a novel framework for rich-media object retrieval is described. The searchable items are media representations consisting of multiple modalities, such as 2-D images, 3-D objects and audio files, which share a common semantic concept. The proposed method utilizes the low-level descriptors of each separate modality to construct a new low-dimensional feature space, where all media objects can be mapped irrespective of their constituting modalities. While most of the existing state-of-the-art approaches support queries of one single modality at a time, the proposed one allows querying with multiple modalities simultaneously, through efficient multimodal query formulation, and retrieves multimodal results of any available type. Finally, a multimedia indexing scheme is adopted to tackle the problem of large scale media retrieval. The present framework proposes significant advances over existing methods and can be easily extended to involve as many heterogeneous modalities as possible. Experiments performed on two multimodal datasets demonstrate the effectiveness of the proposed method in multimodal search and retrieval.