Page 133 - AC/E Digital Culture Annual Report

The studies show that, using Meshlab open-code software, free 123D Catch software and Agisoft PhotoScan Pro licensed software, photogram- metric techniques can be employed in any project for digitally documenting heritage owing to the lower investment required, and that the results are acceptable in comparison to thoseof costlier techniques such as 3D laser scanning. The idea is for the methodology employed in this study to be e ectively implemented for the use of sector professionals.1.5 RTI (Re ectance Transformation Imaging)RTI (Re ectance Transformation Imaging) isa computational photography method. By capturing several digital photographs which are then synthesised, it allows three-dimensional images to be obtained to enhance the object’s surface shape and colour attributes and re-light it interactively from several directions in order to capture details and nuances that result ina digital model as close as possible to the real object.This technique has had major repercussions in the heritage eld, especially with respect to elements with more complex surfaces owingto their composition or particular and/or de- teriorated morphology. Unlike the information obtained from a digital photograph, for an RTI image multiple (2D) photographs need to be shot from a stationary camera position, and for each one light is projected from a di erent direction controlled by the team. Lighting information from all the photographs of the subject is syn- thesised to generate an interactive (3D) imageof the same subject with varying highlights and shadows.It is therefore only logical that RTI techniques, combined with photogrammetry, have gained prominence in the eld of digital documentation, where models need to represent the originals as realistically as possible, reproducing the same con-ditions as if we were observing it in situ. The use of RTI techniques has made it possible to reveal details of the cultural object that would be very di cult to perceive with the naked eye, but which these 3D digital photographs disclose because they survey and analyse the surface in depth.Some companies like Cultural Heritage Imaging are at the forefront of the methodology, data acquisition and visualisation of RTI images, as shown by the corporation’s website,45 which explains some of the technical speci cations and examples of the use of RTI for anyone interested in employing it to document heritage.El Morro National Monument (New Mexico)CHI (Cultural Heritage Imaging)46 is a corpo- ration based in San Francisco (United States) which develops useful imaging tools for digitally documenting heritage treasures before they disappear. This philosophy underpinned the proj- ect focused on the inscriptions and petroglyphs on the rocks of El Morro National Monument,a park in New Mexico whose origins date back to the 1st century AD, when it was occupied by the ancient Zuni Indians. It was subsequently occupied by Spanish settlers in the late sixteenth and early seventeenth centuries. The important historical and documentary value of the inscrip- tions found on the rocks is part of the historical memory of these settlers. These inscriptions have remained for centuries and are one of the attractions for visitors to the park.In 2015, in collaboration with the US National Park Service and Center of Preservation Re- search of the University of Colorado (Denver), CHI was entrusted with carrying out work on these inscriptions carved in sandstone, which were at risk of disappearing due to erosion. The techniques used were small-scale 3D photogram- metry to document the inscriptions in ne detail and RTI (Re ectance Transformation Imaging).47 The combination of these two processes is an ideal means of salvaging inscriptions that areAC/E DIGITAL CULTURE ANNUAL REPORT 2017133The use of digital technologies in the conservation, analysis and dissemination of cultural heritage