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.

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.

No abstract

Very large triangle meshes, i.e. meshes composed of millions of faces, are becoming common in many applications. Obviously, processing, rendering, transmission and archival 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 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 Octreebased 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 lowcost 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.

Many sophisticated solutions have been proposed to reduce the geometric complexity of 3D meshes. A slightly less studied problem is how to preserve attribute detail on simplified meshes (e.g., color, highfrequency shape details, scalar fields, etc.). We present a general approach that is completely independent of the simplification technique adopted to reduce the mesh size. We use resampled textures (rgb, bump, displacement or shade maps) to decouple attribute detail representation from geometry simplification. The original contribution is that preservation is performed after simplification by building a set of triangular texture patches that are then packed into a single texture map. This general solution can be applied to the output of any topology-preserving simplification code and it allows any attribute value defined on the high-resolution mesh to be recovered. Moreover, decoupling shape simplification from detail preservation (and encoding the latter with texture maps) leads to high simplification rates and highly efficient rendering. We also describe an alternative application: the conversion of 3D models with 3D procedural textures (which generally force the use of software renderers) into standard 3D models with 2D bitmap textures.

No abstract

A new system for the construction of highly realistic models of real free-form 3D objects is proposed, based on the integration of several techniques (automatic 3D scanning, inverse illumination, inverse texture-mapping and textured 3D graphics). Our system improves the quality of a 3D model (e.g. acquired with a range scanning device) by adding color detail and, if required, high frequency shape detail. Detail is obtained by processing a set of digital photographs of the object. This is carried out by performing several subtasks: to compute camera calibration and position, to remove illumination effects obtaining both illumination-invariant reflectance properties and a high resolution surface normal field, and finally to blend and stitch the acquired detail on the triangle mesh via standard texture mapping. In particular, the smooth join between different images that map on adjacent sections of the surface is obtained by applying an accurate piecewise local registration of the original images and by blending textures. For each mesh face which is on the adjacency border between different observed images, a corresponding triangular texture patch can also be resampled as a weighted blend of the corresponding adjacent image sections. Examples of the results obtained with sample works of art are presented and discussed.

The paper presents a simple and eficient algorithm for the removal of small topological inconsistencies and high frequency details from surface models. The method, called Marching Intersections (MI), adopts a volumetric approach and acts as a resampling filter: all the intersection points between the input model and the lines of a user selected 3 0 reference grid are located and then, beginning from these intersections, an output surface is reconstructed. MI, which presents good characteristics in terms of eficiency, compactness, and quality of the output models, can be also used: for the conversion between different representation schemes; to p e~o r m logical operations on geometric models; for the topological simplijcation of surfaces; and for the simplification of huge meshes, i.e. meshes too large to be allocated in main memory during the simplijcation process. All these aspects are discussed in the paper and timing and graphic results are presented.