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Item Recurring Part Arrangements in Shape Collections(The Eurographics Association and John Wiley and Sons Ltd., 2014) Zheng, Youyi; Cohen-Or, Daniel; Averkiou, Melinos; Mitra, Niloy J.; B. Levy and J. KautzExtracting semantically related parts across models remains challenging, especially without supervision. The common approach is to co-analyze a model collection, while assuming the existence of descriptive geometric features that can directly identify related parts. In the presence of large shape variations, common geometric features, however, are no longer sufficiently descriptive. In this paper, we explore an indirect top-down approach, where instead of part geometry, part arrangements extracted from each model are compared. The key observation is that while a direct comparison of part geometry can be ambiguous, part arrangements, being higher level structures, remain consistent, and hence can be used to discover latent commonalities among semantically related shapes. We show that our indirect analysis leads to the detection of recurring arrangements of parts, which are otherwise difficult to discover in a direct unsupervised setting. We evaluate our algorithm on ground truth datasets and report advantages over geometric similarity-based bottom-up co-segmentation algorithms.Item 3D Timeline: Reverse Engineering of a Part-based Provenance from Consecutive 3D Models(The Eurographics Association and John Wiley and Sons Ltd., 2014) Dobos, Jozef; Mitra, Niloy J.; Steed, Anthony; B. Levy and J. KautzWe present a novel tool for reverse engineering of modeling histories from consecutive 3D files based on a timeline abstraction. Although a timeline interface is commonly used in 3D modeling packages for animations, it has not been used on geometry manipulation before. Unlike previous visualization methods that require instrumentation of editing software, our approach does not rely on pre-recorded editing instructions. Instead, each stand-alone 3D file is treated as a keyframe of a construction flow from which the editing provenance is reverse engineered. We evaluate this tool on six complex 3D sequences created in a variety of modeling tools by different professional artists and conclude that it provides useful means of visualizing and understanding the editing history. A comparative user study suggests the tool is well suited for this purpose.Item ShapeSynth: Parameterizing Model Collections for Coupled Shape Exploration and Synthesis(The Eurographics Association and John Wiley and Sons Ltd., 2014) Averkiou, Melinos; Kim, Vladimir G.; Zheng, Youyi; Mitra, Niloy J.; B. Levy and J. KautzRecent advances in modeling tools enable non-expert users to synthesize novel shapes by assembling parts extracted from model databases. A major challenge for these tools is to provide users with relevant parts, which is especially difficult for large repositories with significant geometric variations. In this paper we analyze unorganized collections of 3D models to facilitate explorative shape synthesis by providing high-level feedback of possible synthesizable shapes. By jointly analyzing arrangements and shapes of parts across models, we hierarchically embed the models into low-dimensional spaces. The user can then use the parameterization to explore the existing models by clicking in different areas or by selecting groups to zoom on specific shape clusters. More importantly, any point in the embedded space can be lifted to an arrangement of parts to provide an abstracted view of possible shape variations. The abstraction can further be realized by appropriately deforming parts from neighboring models to produce synthesized geometry. Our experiments show that users can rapidly generate plausible and diverse shapes using our system, which also performs favorably with respect to previous modeling tools.