Recording Layers and Plana

A planum must first be prepared before being surveyed so that the procedure is as efficient as possible. The scientists/ technicians should mark out object contours, set out the section nails and position the section divider strings in preparation. Object numbers can be assigned as far as is possible as these can be automatically coded and drawn by the program. Any section identifiers that have already been assigned can also be entered in the program. Walkie-talkies are essential pieces of equipment on an excavation to allow the surveying team to agree on coding over long distances.

The surveying technique used to record an object in the planum depends on the object contour. A straight line can be recorded using just two points whereas an amorphous, curvilinear object must be surveyed using points which are much closer together. The plan is processed in ArchaeoCAD using so-called polyline arcs, which are defined by a start point, a vertex point and an end point. The person setting up the reflectors should also indicate where they have begun recording each object contour during surveying using a planum marker. The last point of a closed object should lie a few centimetres away from the first point. If the contour cannot be closed, a break code must be entered in the total station. It should also be ensured that a new object is generated when a certain preset distance is exceeded i.e. that the last surveyed object contour is automatically closed.

In our experience, even semi-skilled helpers can easily carry out planum recording. This is true for both total station surveying once the total station has been stationed and for surveying objects that have been marked out by scientists. The various work stages are differentiated by using different codings. The basic measuring procedures which must be executed include the surveying of humus levellings, excavation boundaries, area levellings, object contours (poss. with object number), section nails (poss. with section identifier), photogrammetry control points and scattered finds measurements (differentiated by finds group and with their finds label number). These procedures are pre-defined in ArchaeoCAD and must be appropriately coded. The various layers/plana are automatically drawn and differentiated through layer and planum coding, this means that they can be opened, closed and combined as required.

Surveying a stratigraphic excavation is principally the same. The interior area of a layer can be overlaid with an additional levelling grid of greater or lesser density which is coded with the appropriate layer number. Landscape models can be generated on computer using these levelling points by employing additional software which can illustrate layers in three dimensions, creating wiremesh models or contour line graphics (Digital Terrain Model). A gradient module is also included for illustrating three-dimensional relationships. If a scientist additionally wishes to differentiate between the various feature groups, for example post holes, settlement pits, occupation layers, skeleton or urn graves etc., s/he can do this using the respective total station codes. In this way, all coded posthole features, for example, will automatically be entered on their own plan transparency (layer).

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