A Development Perspective of Point-Based Computer Graphics

Every object has its characteristic shape, appearance and responses to physical interactions. Computer graphics center on those three components of an object to bring them onto the computer display. With the rapid development of three dimensional (3D) printing technology, the accuracy of the focused object’s geometry was put forward. Point-based graphing is a way to taking the role in rendering the huge 3D sampled data. Based on the digital geometry processing of point-sampled model, various algorithms were reviewed, and some related key techniques were compared with the potential perspective of the future work in this area was also presented．

Special Issue on Digital Geometry Processing for Large-Scale Structures and Environments

The application of digital geometry processing is undergoing an extension from small industrial products to large-scale structures and environments, including plants, factories, ships, bridges, buildings, forests, and indoor/outdoor/urban environments. This extension is being supported by recent advances in long-range 3D laser scanning technology. Laser scanners are mounted on various platforms, such as tripods, wheeled vehicles, airplanes, and UAVs, and the laser scanning systems are used to efficiently acquire dense and accurate digitized 3D data of the geometry, called point clouds, of large-scale structures and environments. As another technology for the acquisition of digital 3D data of structures and environments, 3D reconstruction methods from digital images are also attracting a great deal of attention because of their flexibility. The utilization of digital 3D data for various purposes still has many challenges, however, in terms of data processing. The extraction of accurate and meaningful information from the data is an especially important and difficult problem, and many studies on object and scene recognition are being conducted in many fields. How to acquire useful and high-quality digital 3D data of large-scale structures and environments is another problem to be solved for digital geometry processing to be widely used. This special issue addresses the latest research advances in digital geometry processing for large-scale structures and environments. It covers a broad range of topics in geometry processing, including new technologies, systems, and reviews for 3D data acquisition, recognition, and modeling of ships, factories, plants, forests, river dikes, and urban environments. The papers will help the readers explore and share their knowledge and experience in technologies and development techniques in this area. All papers were refereed through careful peer reviews. We would like to express our sincere appreciation to the authors for their excellent submissions and to the reviewers for their invaluable efforts in producing this special issue.

A Photogrammetry-Based Workflow for the Accurate 3D Construction and Visualization of Museums Assets

Nowadays digital replicas of artefacts belonging to the Cultural Heritage (CH) are one of the most promising innovations for museums exhibitions, since they foster new forms of interaction with collections, at different scales. However, practical digitization is still a complex task dedicated to specialized operators. Due to these premises, this paper introduces a novel approach to support non-experts working in museums with robust, easy-to-use workflows based on low-cost widespread devices, aimed at the study, classification, preservation, communication and restoration of CH artefacts. The proposed methodology introduces an automated combination of acquisition, based on mobile equipment and visualization, based on Real-Time Rendering. After the description of devices used along the workflow, the paper focuses on image pre-processing and geometry processing techniques adopted to generate accurate 3D models from photographs. Assessment criteria for the developed process evaluation are illustrated. Tests of the methodology on some effective museum case studies are presented and discussed.

Mesh repairing using topology graphs

Geometrical and topological inconsistencies, such as self-intersections and non-manifold elements, are common in triangular meshes, causing various problems across all stages of geometry processing. In this paper, we propose a method to resolve these inconsistencies using a graph-based approach. We first convert geometrical inconsistencies into topological inconsistencies and construct a topology graph. We then define local pairing operations on the topology graph, which is guaranteed not to introduce new inconsistencies. The final output of our method is an oriented manifold with all geometrical and topological inconsistencies fixed. Validated against a large data set, our method overcomes chronic problems in the relevant literature. First, our method preserves the original geometry and it does not introduce a negative volume or false new data, as we do not impose any heuristic assumption (e.g. watertight mesh). Moreover, our method does not introduce new geometric inconsistencies, guaranteeing inconsistency-free outcome.