The mining archaeology research division supports projects all over the world. To ensure that the data gathered at excavations are standardized, comparable, and suitable for scientific analysis, we have developed guidelines and work processes for digital excavation and documentation technology.
GPS devices and tachymeters are used for surveying; if necessary the measurement data are supplemented with 2D or 3D scanners. Photographic documentation is carried out with digital SLR cameras, and specially adapted lenses. To photograph large spaces, we use a broad spectrum of camera supports. This ranges from a simple five-metre-long pole with a camera mount, to manned aircraft and drones. We also obtain high-resolution satellite images to visually document whole areas, and supplement the digital data with recordings from geophysical measuring instruments.
The data from the archaeological fieldwork are recorded digitally in a database while the excavation is taking place. In keeping with the high quality of the raw data, we apply modern methods of processing, visual representation and analysis.
In excavations of historic mines, the focus in underground areas is on cavity surveying and the graphic representation of the results. For the above-ground areas, photogrammetric image analysis is becoming increasingly important, especially for the documentation of outlines and sections. The photomaps, which are often produced while the excavation is still underway, are used to interpret the findings and as a basis for further maps in CAD and GIS systems. All the information is then consolidated at GIS workstations, to ensure that it is placed in a comprehensive and analysable context.
Documentation of underground cavities
Surveying is an indispensable instrument of archaeology. In the field of mining archaeology, the challenge lies in the measurement of complex three-dimensional cavities.
Specialized documentation processes are used to create 3D computer models: it is possible to “travel” through these virtually, and consider them from all sides. In this way the observer gets an idea of how the cavities are situated in relation to one another – an impression which is never possible in the real world. Spherical panorama photographs also give a photo-realistic impression of what it looks like underground.
3D models supply mining archaeologists with even more information about the cavities, such as their precise extent, dimensions and volume. This makes it possible to quantify the work carried out by the miners: in combination with mineralogical studies on the ore content, we can draw conclusions about both the total volume mined and the quantity of the actual raw material extracted. This also allows for comparisons between different cavities, thus giving insight into the significance of the mine in its time.
From light-section device to profile scanner
30 years ago we developed a light-section device to quickly and conveniently survey (adit) cross-sections. It produces a narrow strip of light on the walls of the otherwise dark adit. Reflectors are situated at a certain, known distance from one another, and appear as points of light in the photo. After image restitution, a true-to-scale outline of the cavity appears, which then has to be transferred to the computer.
In 2003, together with partners from the field of speleology, we developed a handy 2D profile scanner: within just a few seconds it can measure (adit) cross-sections on one plane. If the cross sections are taken at short intervals (approx. 30 cm), they can be meshed into a 3D model. This enables mining archaeologists to obtain direct digital documentation of several hundred cross-sections per day.
At present we are working on the third generation of instruments, with partners from the fields of electrical engineering and computer science: the profile scanner is now lighter, thanks to a technical modification, and will in future offer greater measuring accuracy and higher resolution. The cross-sections produced in this way can be placed directly in the 3D space in the correct position, using a built-in tilt-compensated compass module. A camera module to simultaneously gather image information is planned as an optional extra.
Use of geo-coded image material
Archaeological studies usually begin with prospection. For this, a particular area is systematically explored and the findings are documented. Here direct linking of GPS and camera data is a useful addition to archaeological documentation. The inherent discrepancy between the camera location and the subject of the image can be accounted for by simultaneously recording the direction of the camera. Significant added value comes from digital processing, which has to supply current and future scholars with the comprehensive documentation they require.
The mining archaeology research division has around 3000 medium-format slides, 50,000 small-format slides and 90,000 digital photos, with an annual increase of around 6000 to 8000 photos. In order to be able to work with these quantities, we are constructing a mining-specific image database. In combination with the GPS data, it will be possible to combine queries on specific topics with geographical information.
In conjunction with the various photogrammetric software products available, the photogrammetric system of documentation is becoming more and more important for us and others in this field. Both simple 2D image restitution for flat objects and orthophoto computation for non-flat surfaces are increasingly becoming part of everyday excavation work.
Photomaps are created in situ, and are used as the basis for subsequent archaeological mapping. The combination of time-saving and objective photogrammetric documentation with interpretative thematic drawing thus combines the advantages of both techniques.
Database with GIS connection
Since 2008 we have been developing a database system for the special requirements of the mining archaeology projects, a system which reflects the complex descriptive elements of this archaeological research. The relevant geometric information from the tachymetric measurements can be automatically linked with the technical data by way of a coding system. Modules for incorporating graphic documentation materials complete the database system. Any information from the database ¬– as long as it contains a geographical reference – can be incorporated into a GIS for further analyses.
In the GIS laboratory we initiate and devise tailor-made GIS solutions, mainly for the DBM’s archaeological projects. With project partners from e.g. archaeology, archaeometry, surveying or soil science, we develop systems to coordinate the data from the different subjects, and to bring them together for integral analysis. We support all stages of work: from the obtaining of geodata, data conversion, the integration of databases, quality control and general GIS analysis, to the final visual representation.