A stratigraphic approach
Why a stratigraphic granularity in virtual reconstruction ?
The main focus of the stratigraphic reading is the chronological sequence (what is newer, what is older) and for that reason is finer compared with other segmentations that identifies only the function of the objects. In other words, a stratigraphic reading does not only take into account the functional units (a wall, a floor) but subdivide them in their chronological transformations (i.e. wall creation, first restoration of the wall, creation of a window that cut the wall and its restoration, the window has been transformed into a door, the door is walled back, etc..). Working both with big sites like the Imperial Fora or with a small emergency excavation it is possible to follow the same methodology maintaining data consistency.
A granularity matter and the archaeological stratigraphy
As in figure 1, current limitations in virtual reconstruction are mainly in the data granularity: (a) the model obtained from the survey, or “reality based model”, (b) the “source granularity approach”: the model is divided according to a single source typology (square brackets) but each segment is normally based on different sources blended together (curly brackets). In this approach, the process used to obtain the stratigraphic unit from its sources remains only “into the mind of the archaeologists”. (c) The proposed approach: it is possible to provide the source details for each SU. (d) The Extended Matrix regarding the previous Figure c. Taking in mind this situation, the EM granularity is based on the archaeological stratigraphy: it permits to have a per-object description of the reconstruction processes.
Common equivocacies about stratigraphic reading
A very common equivocacy about stratigraphy is that it concerns just earth strata or remains. The importance that archaeologists grant to the stratigraphy is directly connected to the need to have a tool as much “wide” as possible in term of semantic representation: dealing with a brush stroke on a canvas (painting stratigraphy annotation from x-ray), trees on a landscape, deposits of earth, architectonical elements or graffiti carved in a painted wall, the tool used is the same: the SU. It has a wide scope: it means “result of an action” and it is intended to be applied to every cultural element on a chronological timeline. These actions can be natural (earthquake interface of destruction, a tree, an interface of a flooding from the near river) or anthropic (a foundation, a lintel, the decoration of a lintel etc..). An interesting thing is that the SU, despite the fact that it can refer to different objects, can have always a precise and actual 4D representation (time and geometry).
From a virtual reconstruction point of view, the most valuable aspect of the stratigraphic approach however is not only in its ductility of scenarios of use but in the possibility to annotate “negative” actions (and, in turn, the gaps in an existent “structure”): it is a convenient way to classify the elements that have been removed and have to be restored (reconstructed).