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ABSTRACT:This paper describes two procedures used to disseminate tangible cultural heritage through real-time 3D simulations providing accurate-scientific representations. The main idea is to create simple geometries (with low-poly count) and apply two different texture maps to them: a normal map and a displacement map. There are two ways to achieve models that fit with normal or displacement maps: with the former (normal maps), the number of polygons in the reality-based model may be dramatically reduced by decimation algorithms and then normals may be calculated by rendering them to texture solutions (baking). With the latter, a LOD model is needed; its topology has to be quad-dominant for it to be converted to a good quality subdivision surface (with consistent tangency and curvature all over). The subdivision surface is constructed using methodologies for the construction of assets borrowed from character animation: these techniques have been recently implemented in many entertainment applications known as "retopology". The normal map is used as usual, in order to shade the surface of the model in a realistic way. The displacement map is used to finish, in real-time, the flat faces of the object, by adding the geometric detail missing in the low-poly models. The accuracy of the resulting geometry is progressively refined based on the distance from the viewing point, so the result is like a continuous level of detail, the only difference being that there is no need to create different 3D models for one and the same object. All geometric detail is calculated in real-time according to the displacement map. This approach can be used in Unity, a real-time 3D engine originally designed for developing computer games. It provides a powerful rendering engine, fully integrated with a complete set of intuitive tools and rapid workflows that allow users to easily create interactive 3D contents. With the release of Unity 4.0, new rendering features have been added, including DirectX 11 support. Real-time tessellation is a technique that can be applied by using such technology. Since the displacement and the resulting geometry are calculated by the GPU, the time-based execution cost of this technique is very low.

This paper describes the virtual reconstruction of a late fifteenth century terracotta statue. The proposed solution was adopted during the restoration process when it was not possible to get back the fragments from the missing parts that were lost during the burial period. The archaeological statue that has been called 'Crist del Fossar', according to its morphology and provenance, was found severely damaged, as it appeared highly fragmented with dull and age-worn edges. The restoration was assisted by means of an automatic reassembly technique that operates on digital models of fragments. This technique considers the best alignments between themselves (without the need to manipulate the original ones) and leads the reassembly and adhesion processes of the fragments. The statue will be part of a temporary exhibition at the Museu de Prehistòria de València where visitors would be able to appreciate the restoration of the few fragments that have been conserved and will be able to explore the virtual reconstruction of the entire statue through an immersive 3D interactive visualization

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ResumenEn este artículo se presenta un método automático para la reconstrucción de fragmentos arqueológicos, basado en técnicas de correspondencia de patrones desarrolladas en el ámbito de la informática gráfica y el análisis de imágenes. El método se plasma en el desarrollo de una herramienta informática que permita obtener las mejores correspondencias entre un conjunto de fragmentos caracterizados bidimensionalmente. Para garantizar la eficiencia del resultado, se ha desarrollado un estudio teórico que permite dar solución al problema considerado garantizando la corrección de los resultados, y con tiempos de ejecución muy competitivos. Palabras Clave: RECONSTRUCCIÓN DE FRAGMENTOS, CORRESPONDENCIA DE PATRONES, REGISTRO DE SUPERFICIES, ANÁLISIS DE IMÁGENES Abstract This paper introduces a method for automatic archaeological fragment reconstruction, based on the pattern matching techniques originally developed in graphic computing and image analysis fields. The method is embodied in a software tool that provides the bests matches in a set of bi-dimensional archaeological fragments. To ensure the efficiency of the results, it has been developed a theoretical study that allows solving the stated problem, ensuring the correction of results, and with a very competitive execution times. Key words: PART RECONSTRUCTION, PATTERN MATCHING, SURFACE REGISTRATION, IMAGE ANALYSIS IntroducciónLa correspondencia de patrones es un problema que ha sido estudiado durante muchos años y que sigue sin ser resuelto con un coste computacional acotado. Poder establecer de forma automática similitudes entre patrones permite dar solución a multitud de problemas, como la reconstrucción a partir de fragmentos, el ensamblado de piezas industriales, la síntesis de proteínas… Su aplicación es de especial importancia en el ámbito de la arqueología, ayudando a la recomposición de mosaicos, pinturas murales o elementos cerámicos.Recientemente, han comenzado a surgir técnicas de catalogación y clasificación más o menos automatizadas que se apoyan en dispositivos de adquisición de datos como sensores de visión o escáneres 3D. En (BROWN, 2008) (KOLLER, 2005) se comentan dos proyectos actuales en los que la aplicación de estas técnicas ilustra el potencial que pueden ofrecer las herramientas informáticas.La complejidad de la solución alcanzada es una consecuencia inmediata de que no puedan realizarse búsquedas locales garantizando la exactitud de los resultados. Así, la dimensionalidad del problema estudiado implica una explosión combinatoria en el espacio de búsqueda que afecta gravemente a la eficiencia de las técnicas automáticas.En la actualidad existen dos grandes grupos de metodologías que permiten abordar el problema de la correspondencia: los algoritmos ingenuos (HUTTENLOCHER, 1990), que llevan a cabo una búsqueda exhaustiva garantizando los resultados a expensas de costes computacionales elevados, y los algoritmos aleatorios (FISCHLER, 1981), que reducen la talla del problema obviando parte de los datos, a costa de no garantizar los resultad...

Reconstruction of broken archaeological artifacts from fragments is a very time-consuming task that requires a big effort if performed manually. In fact, due to budgetary limitations, this is not even attempted in countless sites around the world, leaving vast quantities of material unstudied and stored indefinitely.This Thesis dissertation faces the application of surface registration techniques to the automatic re-assembly of broken archaeological artifacts from fragments. To efficiently do so, the reconstruction problem has been divided into two groups: 3 degrees of freedom and 6 degrees of freedom problems. This distinction is motivated for two major reasons: archaeological interest of the application and computational complexity of the solution.First kind of problems (3 degrees of freedom) deal with 2D objects or with flat 3D objects, like ripped-up documents or frescoes, respectively. In both cases, the mural paintings and engravings on the fragments' surface are of huge importance in the field of Cultural Heritage Recovery. In this sense, archaeologically speaking, the value of the reconstruction is not the final model itself, but the information stored in the upper surface. In terms of computation complexity, the reduced solution space allows using exhaustive techniques to ensure the quality of the results, while keeping execution times low. A fast hierarchical technique is introduced to face this kind of problems. Starting from an exhaustive search strategy, the technique progressively incorporates new features that lead to a hierarchical search strategy. Convergence and correction of the resulting technique are ensured using an optimistic cost function. Internal search calculations are optimized so the only operations performed are additions, subtractions and comparisons over aligned data. All heavy geometric operations are carried out by the GPU on a pre-processing stage that only happens once per fragment.Second kind of problems (6 degrees of freedom) deal with more general situations, where no special constraints are considered. Typical examples are broken sculptures, friezes, columns... In this case, computational complexity increases considerably with the extra 3 degrees of freedom, making exhaustive approaches prohibitive. To face this problems, an efficient sparse technique is introduced that uses a pre-processing stage to reduce the size of the problem: singular key-points in the original point cloud are selected based on a multi-scale feature extraction process driven by the saliency of each point. By computing a modified version of the PFH descriptor, the local neighborhood of each keypoint is described in a compact histogram. Using exclusively the selected key-points and their associated descriptors, a very fast one-to-one search algorithm is executed for each possible pair of fragments. This process uses a three-level hierarchical search strategy driven by the local similarity between key-points, and applying a set of geometric consistence tests for intermediate results. Finally, a graph-bas...