Combined use of digital nightlight photography and photogrammetry in the process of petroglyphs documentation: the case of Alcázar de San Juan (Ciudad Real, Spain)

For decades, the documentation of rock art has been the backbone of the research on this cultural practice. However, traditional techniques used for this purpose have proved to be imprecise and subjective. With the advent of the digital age there has been a revolution in the field of rock art documentation in general and in particular for petroglyphs. Techniques such as digital nightlight photography or three-dimensional (3D) photogrammetry have opened a world of possibilities. In the case of nightlight photography, its use goes back to the second half of the 20th century. However, in recent years the emergence of high-power digital cameras along with new lighting systems unthinkable decades ago, such as tactical flashlights, have rejuvenated a technique that seems incombustible. After the numerous tests carried out by the DIPAR (Integral Rock Art Documentation System) project team, it has become evident that, correctly employed, this technique still has immense potential in the field of rock art documentation, especially if we take into consideration its low cost and ease of use. Photogrammetry, on the other hand, is shown as the perfect complement to the records obtained through digital nightlight photography. The possibility of applying filters or shaders that increase the visibility of the digitized petroglyphs, within a metric scheme, is a great advance in their documentation. This paper explores the advantages associated with these techniques with a case study: unpublished petroglyphs of Alcázar de San Juan (Spain).