TECHNIQUES FOR REVEALING 3D HIDDEN ARCHEOLOGICAL FEATURES: MORPHOLOGICAL RESIDUAL MODELS AS VIRTUAL-POLYNOMIAL TEXTURE MAPS

摘要

The recent developments in 3D scanning technologies are not been accompanied by visualization interfaces. We are still using the same types of visual codes as when maps and drawings were made by hand. The available information in 3D scanning data sets is not being fully exploited by current visualization techniques. In this paper we present recent developments regarding the use of 3D scanning data sets for revealing invisible information from archaeological sites. These sites are affected by a common problem, decay processes, such as erosion, that never ceases its action and endangers the persistence of last vestiges of some peoples and cultures. Rock art engravings, or epigraphical inscriptions, are among the most affected by these processes because they are, due to their one nature, carved at the surface of rocks often exposed to climatic agents. The study and interpretation of these motifs and texts is strongly conditioned by the degree of conservation of the imprints left by our ancestors. Every single detail in the remaining carvings can make a huge difference in the conclusions taken by specialists. We have selected two case-studies severely affected by erosion to present the results of the on-going work dedicated to explore in new ways the information contained in 3D scanning data sets. A new method for depicting subtle morphological features in the surface of objects or sites has been developed. It allows to contrast human patterns still present at the surface but invisible to naked eye or by any other archaeological inspection technique. It was called Morphological Residual Model (MRM) because of its ability to contrast the shallowest morphological details, to which we refer as residuals, contained in the wider forms of the backdrop. Afterwards, we have simulated the process of building Polynomial Texture Maps - a widespread technique that as been contributing to archaeological studies for some years - in a 3D virtual environment using the results of MRM calculations. By this, we wish to benefit from the rendering capabilities of RTI-viewer and from its intuitive graphic interface. At the same time, virtual PTM is a way of applying this to areas barred to conventional PTM, like in the case presented of an entire roman city occupying a plateau of several sq. km. The results of this research project are presented and discussed using the two case-studies aforementioned, a Latin inscription from a Roman sanctuary in the north of Portugal and a engraved panel with zoomorphic motifs from a rock art site in the north border of Portugal.