Combining photogrammetry and photographic enhancement techniques for the recording of megalithic art in north-west Iberia

• We use different but complementary techniques to register rock art.
• We have incorporated polarised light photography as an habitual technique.
• Photography techniques are successfully used in non-visible wavelengths.
• Strict photogrammetric processing procedures are used.
• All methods are combined in order to achieve precise digital tracings.

Photogrammetry is an indirect technique that allows one to obtain different recording products – orthophotographs, planimetries, 3D models, etc. – that are essential for the study of prehistoric rock art. We believe nonetheless that there is no single technique capable of effectively registering an entire rock art site, so it is highly recommended to use a combination of several systems – that is to say, the development of a specific recording methodology – in order to obtain a documentation which is as thorough as possible. In this regard, different possibilities of combination of photogrammetry with other photographic techniques have been analysed, with the aim of obtaining an accurate recording of the art and its support, seeking also to incorporate into this recording other essential data for the study of its state of preservation.The use of photogrammetric techniques will be described, along with the tests carried out with photographic techniques such as polarised light photography or those that register images at both ends of the visible spectrum, both in the ultraviolet (UV) and in the infrared region (IR). These techniques enable the revelation of invisible details to clarify issues concerning technology and to explore scarcely noticeable forms of alteration. In some cases, these experiences have been complemented by the use of laser scanning in order to compare the effectiveness of both techniques.With all the experience acquired, it is possible to propose a rather precise recording methodology that requires no specialised technical training and no complex equipment.