Professional SfM and TLS vs a simple SfM photogrammetry for 3D modelling of rock art and radiance scaling shading in engraving detection

Abstract

Abstract The geometric inventory and documentation of rock art present great challenges due to the high number of petroglyphs present in a territory, the distance between them, the state of abandonment of forest areas in many cases, limitations to access, and the geometric characteristics of such art. Structure from motion (SfM) photogrammetry was positioned as an ideal technique for its documentation, but this technique has great variability in its methodology and cost. In this study, an extremely simple and effective method based on SfM photogrammetry with low cost cloud computing software is compared to the use of a terrestrial laser scanner (TLS) and professional SfM workflow to generate 3D models for documenting petroglyphs. The comparison is made on the 3D documentation of the Castrino de Conxo petroglyph in Santiago de Compostela, Spain, and extrapolated to two practical experiments on other petroglyphs. The meshes are compared by analysing visual, geometrical and operational criteria and how they influence the radiance scaling shading. The results show that with a SfM photogrammetry methodology, which is extremely simple and accessible to everyone, it is possible to obtain better results in geometric and visual aspects than those obtained with TLS, and they are valid for a detailed analysis of this type of rock art in a massively social approach of documentation that is not possible through other approaches.