A Pentax (PCS-lS) theodolyte and data recorder (Corvallis Microtechnology Inc. model MC-V-El) were used on the Late Bronze excavations on the island of Ustica (45 miles north of Palermo) this past May and June. Points surveyed were used with AutoCAD to plot the two dimensional plan of the city wall and the huts excavated to date (Fig. 1) as well as to create solid models of the hut walls (Fig. 2). We have been using AutoCAD over the last few years to develop a solid model of the excavation units and automatically generate displays of densities of material recovered from those excavation units. (The requirements to produce sections of the site model by slicing the AutoCAD density model mandate three-dimensional solids which will continue to display density when a unit is sliced.)
In essence, the points taken with the Pentax are stored in the data collector and then dumped to a laptop computer; they can then be put into the AutoCAD model automatically. Special software was developed by Jim Frank of Anderson Equipment Company (also supplier of the equipment); it is accessed through an existing AutoCAD menu and offers a number of options. Specifically, we can survey points to create a topography of the land, a 2-D plan, vertical faces, and 3-D solid models. Key to the software are the identification codes which are stored with each point taken. Any single point can be used for a number of plans (e.g., 2-D plan as well as 3-D models) by the proper assignment of the ID codes. This saves us from taking the same point a number of times, a task which can create slightly different specific points. In managing the data collector, we found that taking points for a topo are the easiest, and solid models the most complex. The software developed allows the editing of the files, including deletion and creation of lines, and editing or moving point elevations or descriptions. Small errors in the field (incorrect assignment of ID, for example) can be edited online avoiding the need to resurvey points. Additionally, use of a specific point for another plot (e.g., 2-dimensional when it was originally taken for a 3-dimensional) can be facilitated through the editor.
It was critical that we establish a set of procedures for surveying and a set of standards for ID codes; once done, the work progressed smoothly. With the previously established fixed points on the site, and the capability with this equipment to store files of set-up points, we readily surveyed the walls in pieces as time permitted and let the software join the parts. Standards for AutoCAD layers (data segments, not stratigraphic layers) for the components of the plans were developed so that we could easily edit and/or replace a surveyed section as required. Placing pieces on different layers also allowed us to choose which layers (and, hence, sections of wall) to display at any time and to present them in different colors or linetypes.
In addition to the 2-dimensional plan and the wire-frame model of the huts, we present a third figure: a plan view of the 3-D model which incorporates the solid models of the hut walls (Fig. 3, detail in Fig. 4) with the solid models of the excavation units. For our purposes we are not attempting to replicate the hut walls exactly (vertical faces would probably do a better job), but to approximate the extant hut walls in conjunction with the excavation units. The software easily serves this purpose and saves us hours of painstaking manual reconstruction. In our AutoCAD drawings of the excavation units we also include icons for those individual finds which we have precisely located. The detail of the drawing (Fig. 4) shows the icons clearly, but they are seen here in black and white. The AutoCAD model uses color as well as size and shape to differentiate.
Turn to a related artricle: Using a Total Station
For other Newsletter articles concerning the applications of CAD modelling in archaeology and architectural history or Pompeii, consult the Subject index.
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