Mapping and 3D Modeling
From the inception of the Wadi el-Hudi Expedition, our survey methods have been focused on goals of complete 3D documentation of the archaeological remains and their surrounding landscapes. We use a LEICA total station to map most of the architecture, artifacts, excavation areas, and inscriptions at each archaeological site. The total station is an optical and electronic instrument that measures slopes and distances to a particular point from the instrument’s location (or “station”). With it, we create highly accurate maps and models of the sites. Furthermore, by mapping a series of transecting lines to geodetic benchmarks around Wadi el-Hudi that have been previously and precisely mapped, we have been able to give Universal Transverse Mercator (UTM) coordinates for all of our sites. This information allows the data to be imported into any geographic information system. That is to say, we can describe precisely where the sites are located and then convey that information to the appropriate academic and governmental audiences.
Also, using a series of photographs taken from overhead we are creating photo-mosaics of the archaeological sites as high-resolution Red-Green-Blue (RGB) maps annotated with architectural lines and topographic contours. These will become definitive published maps of most archaeological sites at Wadi el-Hudi, hopefully to appear in the near future. With this method, we have already achieved a major goal of the survey: the creation of architectural maps for 11 archaeological sites as well as the locations of all of the inscriptions at Wadi el-Hudi. In planning beyond the print publication, we hope to find the funding to process this data and purchase server space to make it all available as a 3D model with cached photographs and annotated features on the Internet. If we are able to return to the desert, we hope to take a series of precise photographs of those sites that have been mapped to help us create 3D models of the inscriptions and settlements for people to walk through virtually, online.
Photogrammetry for epigraphy
In the course of our work at Wadi el-Hudi, we want to republish the 155 inscriptions previously photographed and copied by Ahmed Fakhry along with the 100+ new inscriptions that we have already found and the additional ones we will find in future seasons. When we do so, we want to interpret the inscriptions in their spatial and physical contexts because the meaning of an inscription can change based on how (or even if) it was visible for people to see. Thus, the epigraphic study of the inscriptions at Wadi el-Hudi has necessarily depended upon our 3D surveys of the area. The challenge of undertaking epigraphic work at Wadi el-Hudi is that the inscriptions are carved onto irregular surfaces on rocks. In the past, epigraphers documenting rock inscriptions would lay clear vellum over inscriptions like these in order to copy them. But that technique inherently distorts a 3D inscription, making it appear as a 2D drawing. Moreover, the traditional method is physically challenging, time-consuming, and expensive because a person must do the copying and collating work in the desert.
Instead, the Wadi el-Hudi team is recording the inscriptions as 3D models using photogrammetry with high-resolution digital imagery. Essentially, we take high-resolution photographs and RTI images (described below) of the inscriptions, and we map each of the inscriptions with a total station (see “Mapping and 3D Modelling” above). Using structure-from-motion technology in Agisoft Photoscan, we have incorporated 3d models from the epigraphic study seamlessly into the overall 3D survey of the archaeological sites (see below). With this data, not only can we digitally render the image in 2D so that we can still create traditional line drawings of the inscriptions for publication in books. But this innovative study of the inscriptions as physical parts of their landscapes also allows us to study and represent their meaning that is situated and derived from place, following a methodology outlined by the field of Geosemiotics. This 3D epigraphic study is ongoing.
Applications of photoscanning
We have designed a methodology for using the tools outlined above that allows us to use Agisoft Photoscan as the primary tool in conducting 3D survey of architectural remains at Wadi el-Hudi. Three people can quickly survey standing architecture using a setup with six cameras oriented in different directions at two heights. These photos, taken while walking transects across the sites approximately three meters apart, are then fed into Agisoft Photoscan. This structure-from-motion, photogrammetry-based computer program makes it possible to produce high resolution 3D models using photographs from fieldwork as well as from artifact analysis. With the high-resolution 3D models that this method produces, we digitize maps and plans directly in Agisoft or as an exported file in ArcGIS. For example, an orthophoto of Site 5 produced from the 3D model shows that the 3D model is as accurate as the map of the site that we made in one month’s time using a Total Station alone. Most recently in the 2019 field season we are implementing a new workflow design to produce 3D models from Photoscan, export them, create maps, and check the maps against the standing architecture all within the time limits of the fieldwork. Using this new photogrammetry-based survey methodology, we will be able to complete our architectural survey and site mapping at an astronomically quicker pace and within the limited time left us.
Reflectance transformation imaging (RTI)
Rock inscriptions at Wadi el-Hudi were originally made using two different techniques. First a person could “carve” an inscription by repeatedly tracing specific lines on a stone with a sharp stone or chisel. Otherwise a person would “peck” an inscription, by hitting a rock repeatedly in the same area on a rock or boulder until enough of its surface chipped off to form an image. Both techniques offer challenges in recording. At Wadi el-Hudi, we have used RTI to document the inscriptions on the rock outcrops and boulders in the desert, as well as artifacts and stelae collected during survey and excavation. RTI is a new and simple technology, developed by Cultural Heritage Imaging. This technique uses a series of photographs taken from the same perspective with different angles of light. With these photographs, RTI software can be used to develop a “reflectance” model of the photographed surface.
The technique creates a file that allows us to view the surface while manipulating the angle of light. For copying inscriptions (a.k.a. epigraphy), the reflectance model also yields quantitative information about the physical surface of the stone that the inscription was carved onto. For rock art, this model gives a specific measure of the degree of smoothing of a surface that has resulted from the pecking technique for making an inscription. This is a measure that can determine the amount of time that a carver spent on a particular inscription or area in it. Traditional, drawing-based epigraphy, which does not measure the degree of smoothing, can depict it only with variable degrees of stippling. But the quantitative information which RTI provides is extremely important for publishing these inscriptions because every nuance adds to their correct translation, recording, and historical interpretation.As an innovation for working at Wadi el-Hudi, we have had to devise portable dark-rooms to aid in capturing the right lighting conditions for RTI on rock-inscriptions. Similarly, we have also used this technique on artifacts, like pottery sherds, to show the formation techniques and decoration. RTI has already aided in identifying production techniques used in certain pots that are possibly Nubian due to their techniques of decoration.
Chronometric Survey Techniques
Everyone on the Wadi el-Hudi team is equipped with a Handheld, watch, and camera in addition to our notebooks. All of the photographs that we take and the notebook data we record is geolocated using time-stamps. With this information, someone walking in the desert and for looking for new archaeological sites automatically knows where a photograph was taken or where a note-taker stood when he or she wrote a particular note. After each day, we download the data and photographs taken and plot the course walked by each member of our team on GoogleEarth. In the future, we will be able to call up an area on GoogleEarth and immediately know the photo numbers of every picture taken in a specific area.
We are fortunate that Ahmed Fakhry and Ian Shaw took pictures of Wadi el-Hudi in the late 1940s and 1992 respectively. Those older photos are incredibly important to our current work because we can accurately map how the archaeological sites have changed over time using a technique called Rephotography. First, we locate the exact spot and angle from which the original photographer had taken a picture. Then we reproduce the photograph to the best of our ability according to the time-constraints and equipment that we have available. Overlaying the new photograph onto the old photograph immediately reveals features of the landscape that have changed in the intervening time. Moreover, because we know exactly where the new photo was taken and we have mapped remaining features around it, we can actually map the locations of any changed or missing features from the past photograph. For example, if a gate to a settlement was photographed as well preserved in 1992, and it has since been bulldozed by illegal miners, we can still precisely map where the gate had been using Rephotography.
Petrography is a technique used in ceramic analysis that allows us to look microscopically at clay to understand where pottery originally came from and even give us clues on how pottery was made. In this technique, we cut a 0.3 mm thin section from a pot, mount it on a slide, and look at it under a cross polarizing microscope that changes the direction of light, enabling us to see the minerals, rocks, and organic matter that make up the clay fabric. This information helps us piece together the geological origin of clay, so that we can track where pots came from and where they went; essentially, allowing us to map ancient trade and supply routes. At Wadi el-Hudi, petrography is very important because almost all the pottery that contained vital supplies was imported into the site. Understanding the geological origin of the pottery can help us learn about who supplied food and water to the miners in the desert.