Lo más destacado:• Se presenta una reproducción virtual de cuevas paleolíticas con grabados y pinturas de calidad que combina técnicas fotogramétricas y topográficas.• La metodología de trabajo fotogramétrico permite alcanzar una reproducción fiel tanto de la geometría como de la apariencia de las cuevas.• Se apuesta por la divulgación mediante técnicas de realidad virtual inmersiva y métodos interactivos de visualización. Abstract:We present three case studies illustrating the virtual reproduction of caves that belong to the most important artistic ensemble of the Paleolithic from Bizkaia (Spain): Benta Laperra, Askondo and Lumentxa. The complex morphology of the cavities, the fineness of their engravings and the poor definition of their paintings imply technical difficulties to achieve faithful reproduction of their geometry and appearance. The methodology applied in these caves, based on a combination of photogrammetric and surveying techniques, allows the creation of a complete virtual replica, without shadow zones and a detailed reproduction of their engravings and paintings. At the same time, this replica has given rise to a type of technical documentation that very faithfully and objectively facilitates the analysis and interpretation of the cave. On the one hand, series of longitudinal and transverse sections have been generated, extracting information of the cut profile and the projection of the surfaces through orthoimages of elevation-section with a level of resolution of 2 mm per pixel, equivalent to a scale of representation 1/10. In addition, the georeferencing of the caves has allowed the research team to generate cartography of elevations of floor and ceiling by means of contour lines and to overlap the cartography of the National Geographic Institute (IGN) to measure the distance that separates the ceiling of the cave from the external surface. It can be used to detect critical points that must be taken into account in case of possible actions in forestry or infrastructure projects. Finally, these virtual replicas allow the dissemination of a wealth in detail, through new interactive methods of visualization and virtual reality. In conclusion, the presented methodology means an advance with respect to the existing techniques thus providing solutions for both technical and informative applications.Keywords: virtual archaeology; 3D reconstruction; close-range photogrammetry; orthoimage; parietal art; surveying Resumen:Presentamos tres casos de estudio que ilustran la reproducción virtual de las cuevas pertenecientes al conjunto artístico más importante del paleolítico en Bizkaia (España): Benta Laperra, Askondo y Lumentxa. La compleja morfología de las cavidades, la finura de sus grabados y la poca nitidez de sus pinturas suponen dificultades técnicas para lograr la reproducción fiel de su geometría y apariencia. La metodología aplicada en estas cuevas, basada en una combinación de técnicas fotogramétricas y topográficas, permite la creación de una réplica virtual completa, con inexistencia de zon...

Software tools for photogrametric and multi-view stereo reconstruction are nowadays of generalized use in the digitization of architectural cultural heritage. Together with laser scanners, these are well established methods to digitize the three-dimensional geometric properties of real objects. However, the acquired photographic colour mapping of the resulting point clouds or the textured mesh cannot differentiate the proper surface appearance from the influence of the particular illumination present at the moment of the digitization. Acquisition of the actual surface appearance, separated from the existing illumination, is still a challenge for any kind of cultural heritage item, but very specially for architectural elements. Methods based on systematic sampling with commuting light patterns in a laboratory set-up are not suitable. Immovable and outdoor items are normally limited to the existing and uncontrolled natural illumination. This paper demonstrates a practical methodology for appearance acquisition, previously introduced in (Martos and Ruiz, 2013), applied here specifically for the production of re-illuminable architectural orthoimages. It is suitable for outdoor environments, where the illumination is variable and uncontrolled. In fact, naturally occurring changes in light among different images along the day are actually desired and exploited, producing an enhanced multi-layer dynamic texture that is not limited to a frozen RGB colour map. These layers contain valuable complementary information about the depth of the geometry, surface normal fine details and other illuminationdependent parameters, such as direct and indirect light and projected self-shadows, allowing an enhanced and re-illuminable ortoimage representation.

This paper describes a new methodology based on the combination of photogrammetric and stereo-photometric techniques that allows creating virtual replicas reproducing the relief in micrometric scale, with a geometric resolution until 7 microns. The finest details of the texture obtained by photogrammetric methods are translated to the relief of the mesh to provide quality 3D printing by additive manufacturing methods. These results open new possibilities for virtual and physical reproduction of archeological items that need a great accuracy and geometric resolution.

ABSTRACT:This paper describes the surveying process performed on the Church of San Ildefonso in Zamora (Spain) using Orthoware © , an innovative photogrammetric software tool specially designed for the digital reconstruction of cultural heritage. This software is the result of intense R&D at Metria Digital after several years producing heritage true orthoimages, plans and full color 3D models in a commercial environment. Orthoware allows true measurements and produces high quality true orthoimages and full color 3D models starting out from conventional digital photographs. This is a progressive tool designed for non-specialist users, providing intuitive and quick methods to visually diagnose the quality of the results.The Church of San Ildefonso in Zamora was built over a previously existing temple whose Romanesque construction dates back to the 11th century, although it is nowadays hidden among extensions and remodelings carried out up until 18th century. With a length of more than 30 meters, the original floor plan of the Church consists on three naves and three apses, although only one nave is visible now, covered by groin vault, and one semicircular apse partially hidden by the current building. The south front maintains the greater part of its Romanesque origins, in spite of being hidden and higher than the present ground level. At the feet of the temple a tower rises, whose first stage is Romanesque but which has been altered by numerous Baroque elements.The objective of the photogrammetric reconstruction was the integral survey of the monument, including its four façades, interior faces and roofs for the production of some true-orthoimages, cross-sections, longitudinal-sections and ground plans at scale 1/50 with an accuracy of 10 mm for the drawings and a pixel size below 10 mm for the synthetic imagery.The usual photogrammetric workflow for producing true-orthoimages and digital 3D models in cultural heritage depends to a great extent on finding and matching homologous features amongst various images. This is a time-consuming, repetitive and blind recognition process requiring some spatial intuition and experience from the user. Orthoware makes use of automatic image analysis and computer vision techniques to improve this processing. Its innovative graphic user interface allows full interactivity and corrections or refinements to be performed at any time providing intuitive diagnostics from partial results. This flow involves very intensive calculations achieved through a software development specific for GPU (Graphic Processing Unit), using OpenGL (Open Graphics Library) and DirectX. Therefore, a combination of manual and automatic techniques makes up the ideal tool for a production environment. The workflow presented herein allow users to reduce orthoimage production time from months to just a few weeks.