Paolo Cignoni

Metro: measuring error on simplified surfaces

This paper presents a new tool, Metro, designed to compensate for a deficiency in many simplification methods proposed in literature. Metro allows one to compare the difference between a pair of surfaces (e.g. a triangulated mesh and its simplified representation) by adopting a surface sampling approach. It has been designed as a highly general tool, and it does no assumption on the particular approach used to build the simplified representation. It returns both numerical results (meshes areas and volumes, maximum and mean error, etc.) and visual results, by coloring the input surface according to the approximation error.

A comparison of mesh simplification algorithms

Abstract In many applications the need for an accurate simplification of surface meshes is becoming more and more urgent. This need is not only due to rendering speed reasons, but also to allow fast transmission of 3D models in network-based applications. Many different approaches and algorithms for mesh simplification have been proposed in the last few years. We present a survey and a characterization of the fundamental methods. Moreover, the results of an empirical comparison of the simplification codes available in the public domain are discussed. Five implementations, chosen to give a wide spectrum of different topology preserving methods, were run on a set of sample surfaces. We compared empirical computational complexities and the approximation accuracy of the resulting output meshes.

MeshLab: an Open-Source Mesh Processing Tool

The paper presents MeshLab, an open source, extensible, mesh processing system that has been developed at the Visual Computing Lab of the ISTI-CNR with the helps of tens of students. We will describe the MeshLab architecture, its main features and design objectives discussing what strategies have been used to support its development. Various examples of the practical uses of MeshLab in research and professional frameworks are reported to show the various capabilities of the presented system.

Ambient Occlusion and Edge Cueing for Enhancing Real Time Molecular Visualization

The paper presents a set of combined techniques to enhance the real-time visualization of simple or complex molecules (up to order of 106 atoms) space fill mode. The proposed approach includes an innovative technique for efficient computation and storage of ambient occlusion terms, a small set of GPU accelerated procedural impostors for space-fill and ball-and-stick rendering, and novel edge-cueing techniques. As a result, the users understanding of the three-dimensional structure under inspection is strongly increased (even forstill images), while the rendering still occurs in real time

A low cost 3D scanner based on structured light

Automatic 3D acquisition devices (often called 3D scanners) allow to build highly accurate models of real 3D objects in a cost‐ and time‐effective manner. We have experimented this technology in a particular application context: the acquisition of Cultural Heritage artefacts. Specific needs of this domain are: medium‐high accuracy, easy of use, affordable cost of the scanning device, self‐registered acquisition of shape and color data, and finally operational safety for both the operator and the scanned artefacts. According to these requirements, we designed a low‐cost 3D scanner based on structured light which adopts a new, versatile colored stripe pattern approach. We present the scanner architecture, the software technologies adopted, and the first results of its use in a project regarding the 3D acquisition of an archeological statue.

PolyCube-Maps

Standard texture mapping of real-world meshes suffers from the presence of seams that need to be introduced in order to avoid excessive distortions and to make the topology of the mesh compatible to the one of the texture domain. In contrast, cube maps provide a mechanism that could be used for seamless texture mapping with low distortion, but only if the object roughly resembles a cube. We extend this concept to arbitrary meshes by using as texture domain the surface of a polycube whose shape is similar to that of the given mesh. Our approach leads to a seamless texture mapping method that is simple enough to be implemented in currently available graphics hardware.

Multiresolution Decimation based on Global Error

Due to the surface meshes produced at increasing complexity in many applications, interest in efficient simplification algorithms and multiresolution representation is very high. An enhanced simplification approach together with a general multiresolution data scheme are presented here. Jade, a new simplification solution based on the Mesh Decimation approach has been designed to provide both increased approximation precision, based on global error management, and multiresolution output. Moreover, we show that with a small increase in memory, which is needed to store the multiresolution data representation, we are able to extract any level of detail representation from the simplification results in an extremely efficient way. Results are reported on empirical time complexity, approximation quality, and simplification power. TEL:: +39 050 593304

BDAM — Batched Dynamic Adaptive Meshes for High Performance Terrain Visualization

This paper describes an efficient technique for out‐of‐core rendering and management of large textured terrainsurfaces. The technique, called Batched Dynamic Adaptive Meshes (BDAM), is based on a paired tree structure:a tiled quadtree for texture data and a pair of bintrees of small triangular patches for the geometry. These smallpatches are TINs and are constructed and optimized off‐line with high quality simplification and tristrippingalgorithms. Hierarchical view frustum culling and view‐dependent texture and geometry refinement is performedat each frame through a stateless traversal algorithm. Thanks to the batched CPU/GPU communication model,the proposed technique is not processor intensive and fully harnesses the power of current graphics hardware.Both preprocessing and rendering exploit out‐of‐core techniques to be fully scalable and to manage large terraindatasets.

Speeding up isosurface extraction using interval trees

The interval tree is an optimally efficient search structure proposed by Edelsbrunner (1980) to retrieve intervals on the real line that contain a given query value. We propose the application of such a data structure to the fast location of cells intersected by an isosurface in a volume dataset. The resulting search method can be applied to both structured and unstructured volume datasets, and it can be applied incrementally to exploit coherence between isosurfaces. We also address issues of storage requirements, and operations other than the location of cells, whose impact is relevant in the whole isosurface extraction task. In the case of unstructured grids, the overhead, due to the search structure, is compatible with the storage cost of the dataset, and local coherence in the computation of isosurface patches is exploited through a hash table. In the case of a structured dataset, a new conceptual organization is adopted, called the chess-board approach, which exploits the regular structure of the dataset to reduce memory usage and to exploit local coherence. In both cases, efficiency in the computation of surface normals on the isosurface is obtained by a precomputation of the gradients at the vertices of the mesh. Experiments on different kinds of input show that the practical performance of the method reflects its theoretical optimality.

External memory management and simplification of huge meshes

Very large triangle meshes, i.e., meshes composed of millions of faces, are becoming common in many applications. Obviously, processing, rendering, transmission, and archiving of these meshes are not simple tasks. Mesh simplification and LOD management are a rather mature technology that, in many cases, can efficiently manage complex data. But, only a few available systems can manage meshes characterized by a huge size: RAM size is often a severe bottleneck. In this paper, we present a data structure called Octree-based External Memory Mesh (OEMM). It supports external memory management of complex meshes, loading dynamically in main memory only the selected sections and preserving data consistency during local updates. The functionalities implemented on this data structure (simplification, detail preservation, mesh editing, visualization, and inspection) can be applied to huge triangles meshes on low-cost PC platforms. The time overhead due to the external memory management is affordable. Results of the test of our system on complex meshes are presented.