WHPS 2012 had three primary goals. First, to update the collection of photos from the previous survey to a higher quality, specifically those petroglyphs that were poorly photographed. Second, to use RTI and close-range photogrammetry to improve readings of inscriptions that are heavily weathered or otherwise difficult to discern. Furthermore, these techniques will be used to analyze and interpret the layers of overlaid petroglyphs on certain sites to gain more insight into their context within the history of the wadi. Since many of the rock drawings are from different periods, these methods can aid in both differentiating different carving episodes and identifying the tools that were used to create petroglyphs at different times. Third, the creation of gigapixel images of the wadi and certain large-scale petroglyph sites will help demonstrate the landscape context of ancient inscriptions and drawings to a greater degree than has been previously accomplished.
Photogrammetry was the primary technique for imaging the inscriptions and petroglyphs during WHPS 2012. Three types of photogrammetric projects were employed: 1) strip projects comprise multiple strips of overlapping photos to create high resolution 3D models. 2) Convergent pair projects use 2 or more convergent images with near 100% overlap to create very accurate 3D models, though with less resolution. 3) Fan projects are a combination of both, where two or more camera stations photograph dozens or hundreds of images used to create high resolution models of subjects which are too difficult or distant to access. These projects are all built using the ADAMtech software suite. The resulting models are accurate within a tenth of a pixel, which, when using a macro lens, can be accurate on the level of microns.
Gigapixel images are extremely high resolution images, photographed with a high-end DSLR camera on a panoramic tripod head. The resulting images are so-called because the pixel count of such images can number in the billions. There are two different ways of capturing these images: one is a commercially available automated tripod head called a Gigapan, while the other is a manually operated two-axis panorama head called a pano-gimbal head. Gigapixel images can effectively situate the inscriptions and petroglyphs in their wider context within the landscape because they can be stitched together to form 360 degree views. These panoramic images are interactive tools that can be used to explore the landscape. In addition, two or more gigapixel images can be brought into ADAMtech and used as a fan project to construct a photogrammetric model.
Reflectance Transformation Imaging
An RTI is a 2D digital image with imbedded 3D data. The type of 3D data created by an RTI is surface normal information. Surface normal data is used to map the 3D surface of the subject and allows for dynamic re-lighting in RTI viewer to discern shallow relief with raking light from 360 degrees. RTI builder and viewer are free, open-source programs developed by Cultural Heritage Imaging (CHI) and Hewlett-Packard Labs. This technique, while relatively simple to capture in most circumstances, can be cumbersome in extreme environments such as the Wadi Hafir.