Theory

Every archaeological site is stratified and any archaeological stratification – a three-dimensional buried volume - is unique. The stratigraphic excavation method is based upon the distinct excavation of its single units in the reverse order of their deposition or creation. Therefore the archaeologist has to observe and document their stratigraphic relations. These relations are based upon topological observations of the distinct units during the excavation process. They can be deduced as well from a topological analysis of a complete 3D topographical record of these units. If documented, such a complete topographical record provides the possibility for a verification of the stratigraphic sequence or Harris Matrix. During the last years VIAS developed a digital 3D documentation process for stratigraphic excavations in theory and practice which forms the base for future development, necessary to introduce terrestrial laser scanners in the archaeological toolbox.

The standardized process developed for the stratigraphic recording of surfaces is divided into subsequent steps to be repeated for excavated unit of stratification forming a documentation algorithm. Every single unit - surface or deposit - is given a unique number and documented by its boundary polygon as well as its topography. The collected point-clouds from specific surfaces, the surfaces of deposits and the according texture derived from digital photographs are the primary raw data for further mapping and analysis in a GIS. The material aspects of deposits can only be captured by sampling. For the stratigraphic record, each deposit, represented by its top and bottom surface is reduced to a unique number in the stratigraphic sequence. It imparts this number to all of the portable finds and samples found within its volume. Their 3D position can be easily defined upon discovery or extraction. The finds and samples are recorded in 3D space as three dimensional points or small volumes. All further data derived from the finds can be stored in a database, photographs and find drawings.

 It is of major interest, to check the recording during the excavation process. To be able to plan the next steps of excavating, it is important to have all the information from the already excavated deposits at hand. Using conventional means, this can be a very time consuming and often impossible task. During recent years, therefore, we have developed a GIS based procedure for the digital documentation of stratigraphic excavations. The main objective of our work is a standardised digital recording by collecting the fundamental data for a 3D virtual reconstruction of the mass of unique stratification destroyed by the excavation process. The stratigraphic relations of any top surface, bottom surface, or feature interface, have to be observed and recorded. Find and sample records, descriptions and stratigraphic relations are recorded on pre-printed sheets or directly in a database on site referenced by the unique number of the unit of stratification. From these relations, the stratigraphic sequence is formed.