Strat has the capability of combining legacy stratigraphy data from notebooks with contemporary photogrammetric data. By recording this soil-layer or stratigraphic-unit at differing levels of detail we are able to recreate a 3D model on the date and location at which they were excavated. After the entry of only one or two strata we have enough data to give an impression of how the excavation progressed. Sophisticated but easy-to-use tools allow us to navigate our site in 3D and through the use of an animation-bar we are able to easily replay the excavation with only the mouse.

Animating the excavation

The ability to replay the excavation- process is only made possible through the consistent entry into the system of the date the layer was excavated. This information is usually recorded well by archaeologists. An independent dialogue box is used for recording the layer data (Figure 3). If only the depths for the four corners of a trench have been documented the system can nonetheless reconstruct the layer in 3D at its excavated location, which can later be used to replay the excavation. Subsequent to excavation, soil-layers are dated to determine their epoch, for example 400-200BC. Most commonly, layers are dated by the artefacts uncovered within them, the date of which we already know from extensive records. This second element of temporal data enables us to replay the data in a more informative way; by showing the surfaces occupied by successive groups of settlers.
Both these forms of temporal data are stored in a single stratum object, hierarchically, within a relational database. By employing this method, a minimum of two strata need be entered before a sensible replay of the excavation can be made (Figure 1). Pressing the left arrow button allows our excavation to rewind to the start, that is to say where no layers have been excavated. As the user drags the pointer across the slider, soil layers appear in 3D at the date on which they were excavated. This provides a visually appealing real-time animation of the excavation process that would be very difficult to imagine from simply studying the notebooks from previous seasons made by different archaeologists.

The System

Besides the ability to replay excavations the Strat tool serves as a repository for data recorded on a dig; Polaroid photographs, lists of finds, theodolite data, scanned 3D building elements, plan drawings and project information. Strat is flexible in the way that it handles the data. The more data it is supplied, the more detailed and accurate a site model it constructs. If artefacts have been reconstructed in 3D then these can be positioned at the location at which they were discovered. The artefact is represented by a marker if it has not been reconstructed (Figure 7). The GUI has been designed with archaeological requirements at the forefront and functionality has been made automatic wherever possible as to allow minimal intervention from the user. Strat was built from the ground-up using MFC on a Windows platform, using OpenGL libraries for rendering.

The team from the Katholieke Universiteit Leuven under the direction of Professor Marc Waelkens has contributed towards the specification of the archaeological requirements of the stratigraphic tool and provided data for illustrating the tool operating in an archaeological context. We gratefully acknowledge Professor Marc Waelkens, Dr Roland Degeest and their colleagues for this contribution.