A Texture Atlas is an efficient color representation for 3D Paint Systems. The model to be textured is decomposed into charts homeomorphic to discs, each chart is parameterized, and the unfolded charts are packed in texture space. Existing texture atlas methods for triangulated surfaces suffer from several limitations, requiring them to generate a large number of small charts with simple borders. The discontinuities between the charts cause artifacts, and make it difficult to paint large areas with regular patterns.In this paper, our main contribution is a new quasi-conformal parameterization method, based on a least-squares approximation of the Cauchy-Riemann equations. The so-defined objective function minimizes angle deformations, and we prove the following properties: the minimum is unique, independent of a similarity in texture space, independent of the resolution of the mesh and cannot generate triangle flips. The function is numerically well behaved and can therefore be very efficiently minimized. Our approach is robust, and can parameterize large charts with complex borders.We also introduce segmentation methods to decompose the model into charts with natural shapes, and a new packing algorithm to gather them in texture space. We demonstrate our approach applied to paint both scanned and modeled data sets.

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Least squares conformal maps for automatic texture atlas generation

Adaptively Sampled Distance Fields (ADFs) are a unifying representation of shape that integrate numerous concepts in computer graphics including the representation of geometry and volume data and a broad range of processing operations such as rendering, sculpting, level-of-detail management, surface offsetting, collision detection, and color gamut correction. Its structure is uncomplicated and direct, but is especially effective for quality reconstruction of complex shapes, e.g., artistic and organic forms, precision parts, volumes, high order functions, and fractals. We characterize one implementation of ADFs, illustrating its utility on two diverse applications: 1) artistic carving of fine detail, and 2) representing and rendering volume data and volumetric effects. Other applications are briefly presented.

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Adaptively sampled distance fields: a general representation of shape for computer graphics

Given an arbitrary mesh, we present a method to construct a progressive mesh (PM) such that all meshes in the PM sequence share a common texture parametrization. Our method considers two important goals simultaneously. It minimizes texture stretch (small texture distances mapped onto large surface distances) to balance sampling rates over all locations and directions on the surface. It also minimizes texture deviation (“slippage” error based on parametric correspondence) to obtain accurate textured mesh approximations. The method begins by partitioning the mesh into charts using planarity and compactness heuristics. It creates a stretch-minimizing parametrization within each chart, and resizes the charts based on the resulting stretch. Next, it simplifies the mesh while respecting the chart boundaries. The parametrization is re-optimized to reduce both stretch and deviation over the whole PM sequence. Finally, the charts are packed into a texture atlas. We demonstrate using such atlases to sample color and normal maps over several models.

/pdf/texture-mapping-progressive-meshes-1m9elnizzt.pdf

Texture mapping progressive meshes

Rendering throughput has reached a level that enables a novel approach to level-of-detail (LOD) control in terrain rendering. We introduce the geometry clipmap, which caches the terrain in a set of nested regular grids centered about the viewer. The grids are stored as vertex buffers in fast video memory, and are incrementally refilled as the viewpoint moves. This simple framework provides visual continuity, uniform frame rate, complexity throttling, and graceful degradation. Moreover it allows two new exciting real-time functionalities: decompression and synthesis. Our main dataset is a 40GB height map of the United States. A compressed image pyramid reduces the size by a remarkable factor of 100, so that it fits entirely in memory. This compressed data also contributes normal maps for shading. As the viewer approaches the surface, we synthesize grid levels finer than the stored terrain using fractal noise displacement. Decompression, synthesis, and normal-map computations are incremental, thereby allowing interactive flight at 60 frames/sec.

Geometry clipmaps: terrain rendering using nested regular grids

The traditional approach for parametrizing a surface involves cutting it into charts and mapping these piecewise onto a planar domain. We introduce a robust technique for directly parametrizing a genus-zero surface onto a spherical domain. A key ingredient for making such a parametrization practical is the minimization of a stretch-based measure, to reduce scale-distortion and thereby prevent undersampling. Our second contribution is a scheme for sampling the spherical domain using uniformly subdivided polyhedral domains, namely the tetrahedron, octahedron, and cube. We show that these particular semi-regular samplings can be conveniently represented as completely regular 2D grids, i.e. geometry images. Moreover, these images have simple boundary extension rules that aid many processing operations. Applications include geometry remeshing, level-of-detail, morphing, compression, and smooth surface subdivision.

Spherical parametrization and remeshing

Valuable 3D graphical models, such as high-resolution digital scans of cultural heritage objects, may require protection to prevent piracy or misuse, while still allowing for interactive display and manipulation by a widespread audience. We have investigated techniques for protecting 3D graphics content, and we have developed a remote rendering system suitable for sharing archives of 3D models while protecting the 3D geometry from unauthorized extraction. The system consists of a 3D viewer client that includes low-resolution versions of the 3D models, and a rendering server that renders and returns images of high-resolution models according to client requests. The server implements a number of defenses to guard against 3D reconstruction attacks, such as monitoring and limiting request streams, and slightly perturbing and distorting the rendered images. We consider several possible types of reconstruction attacks on such a rendering server, and we examine how these attacks can be defended against without excessively compromising the interactive experience for non-malicious users.

http://vcg.isti.cnr.it/~tarini/pap0A/sigg04A.pdf

Protected interactive 3D graphics via remote rendering

We describe an efficient technique for out-of-core management and interactive rendering of planet sized textured terrain surfaces. The technique, called planet-sized batched dynamic adaptive meshes (P-BDAM), extends the BDAM approach by using as basic primitive a general triangulation of points on a displaced triangle. The proposed framework introduces several advances with respect to the state of the art: thanks to a batched host-to-graphics communication model, we outperform current adaptive tessellation solutions in terms of rendering speed; we guarantee overall geometric continuity, exploiting programmable graphics hardware to cope with the accuracy issues introduced by single precision floating points; we exploit a compressed out of core representation and speculative prefetching for hiding disk latency during rendering of out-of-core data; we efficiently construct high quality simplified representations with a novel distributed out of core simplification algorithm working on a standard PC network.

/pdf/planet-sized-batched-dynamic-adaptive-meshes-p-bdam-12hkp0ennm.pdf

Planet-sized batched dynamic adaptive meshes (P-BDAM)

Multiresolution modeling and visualization of volume data based on simplicial complexes

Many sophisticated solutions have been proposed to reduce the geometric complexity of 3D meshes A problem studied less often is how to preserve on a simplified mesh the detail (eg, color, high frequency shape detail, scalar fields, etc) which is encoded in the original mesh We present a general approach for preserving detail on simplified meshes The detail (or high frequency information) lost after simplification is encoded through texture or bump maps The original contribution is that preservation is performed after simplification, by building set of triangular texture patches that are then packed in a single texture map Each simplified mesh face is sampled to build the associated triangular texture patch; a new method for storing this set of texture patches into a standard rectangular texture is presented and discussed Our detail preserving approach makes no assumptions about the simplification process adopted to reduce mesh complexity and allows highly efficient rendering The solution is very general, allowing preservation of any attribute value defined on the high resolution mesh We also describe an alternative application: the conversion of 3D models with 3D static procedural textures into standard 3D models with 2D textures

A general method for preserving attribute values on simplified meshes

An archeological excavation is usually a rapidly evolving environment: several factors (weather, costs, permissions) force the work to be concentrated in a few weeks. Moreover, excavating is essentially a mono-directional operation, which constantly modifies the state of the site. Since most of the interpretation is performed in a second stage, it is necessary to collect a massive amount of documentation (images, sketches, notes, measurements). In this paper we present an experiment of monitoring of an excavation in Uppakra, South Sweden, using dense stereo matching techniques. The archeologists were trained to collect a set of images every day; the set was used to produce a 3D model depicting the state of the excavation. In this way, it was possible to obtain a reliable geometric representation of the evolution of the excavation. The obtained model were also used by the archeologists, by the means of an open-source tool, to perform a site study and interpretation stage directly on the geometric data. The results of the experimentation show that dense stereo matching can be easily integrated with the daily work of archeologists in the context of an excavation, and it can provide a valuable source of data for interpretation, archival and integration of acquired material.

Roberto Scopigno

Papers

Protected interactive 3D graphics via remote rendering

Planet-sized batched dynamic adaptive meshes (P-BDAM)

Multiresolution modeling and visualization of volume data based on simplicial complexes

A general method for preserving attribute values on simplified meshes

Documentation and interpretation of an archeological excavation: an experience with dense stereo reconstruction tools