Pindal cave, listed as World Heritage by UNESCO since July of this year, can tour in 3D thanks to a research by a team of professors at the Polytechnic School of Avila, who heads Diego González Aguilera.
This team, known as Tidop Research Group (Information Technology for Heritage Documentation) just completed under the supervision of Professor Mario Menéndez, Department of Prehistory and Archaeology at UNED, its comprehensive documentation and metric 3D reconstruction.
But what is the real importance of this work? “The determination of the geometric component in the accurate documentation of the heritage involves the quantification of the special characteristics of the object, especially its shape and dimensions, orientation and location”, profesor González Aguilera explains, “and this operation becomes important in the sense that their results may become the basis for reconstruction and is also a testimony of the prior state to any intervention or modification.”
Pindal cave stands in the vicinity of the town of Pimiango in Ribadedeva (Asturias), near the border with Cantabria. This beautiful corner is well known for some cave paintings discovered in 1908.
TERRESTRIAL LASER SCANNER
Recently, the use of terrestrial laser scanner, used in researches, enables a new approach to the problem of documentation and three-dimensional geometric modeling of the Paleolithic caves and parietal art. According to the studio manager says, this is the land Trimble GX scanner mounted on the Manfrotto 400 swivel that allows spins with three degrees of freedom, necessary to accommodate the position of the scanner to the characteristics of the cave. “The data captured by this team is finally summarized the three-dimensional XYZ coordinates of mesh points and their radiometric values in RGB color system,” points out the technical details González Aguilera.
Basically this laser and two high resolution digital cameras were the tools needed to carry out the fieldwork. “The field work was conducted for five alternate days. They included five members of the group Tidop aided by two operators of the Council.
“Thus it was possible to combine the laser scanning and the photo shoot,” says González Aguilera, further explains that, given the complexity of the geometry inside the cave and the problems caused by occlusions, both for laser scans as for photographic archive was necessary to make a total of 19 laser stations, from which they made general scans of 360º with mesh steps of 2 centimeters in 20 meters, and two shots per point.
“This data collection configuration ensured more than 15% of overlapping between the point clouds obtained, thereby having a guarantee for proper fusion of the point clouds”, says the professor of the Polytechnic. In fact, a total of 33 million points in XYZ coordinates were obtained for the geometrical definition of the interior of the cavern.
On the other hand were the photo sessions that involved two different types of work: a set of shots to complete the work of the laser, through the ability to provide high-resolution photographic texture to the point cloud, and another set of shots with the fisheye lens for the generation of linked panoramas that allow us to generate a virtual visit. For this 25 photographic stations were chosen from which we made the seven necessary shots to compose each of the 25 panoramas.
COMPUTER PROCESSING
After the processing of all the data the team obtained a ground orthophoto. “It shows a top view of the cave, which can be considered as a precise and detailed plan of the cave”, begins to list his conclusions Professor González Aguilera. Furthermore, orthophotos of the cave paintings room and a textured 3D model were obtained. “This is an interactive model through which you can navigate, retaining the metric properties and being able to see the object from inaccessible points of view,” says the teacher, pointing this advantage of the system.
Diego González Aguilera explains that from the data obtained has been possible to draw another set of tools and applications that have resulted in obtaining virtual flights, that is, a number of video files generated from the laser three-dimensional models, as well as a virtual tour that has been generated by coherent composition of the whole panoramic photographs taken before and also has been able to generate transverse and longitudinal sections of the cave. With this work done in the environment that will, among other things, better and wider dissemination of the cave is complete. With this the work is completed and it will allow, among other things, a better and wider dissemination of the cave.