Regular readers of the CSA Newsletter may recall discussions of the CSA Layer Naming Convention that began as early as the very first issue of the Newsletter in May, 1988. It was clear, even then, that the system of dividing complicated models into segments (CAD layers) and then naming those segments was very important to the effective application of CAD technology. Eventually the CSA Layer Naming Convention (http://csanet.org/inftech/csalnc.html) was produced and subsequently modified. That convention, of course, has been used to determine the layer names and naming system for the CSA Propylaea Project.
Readers who are not familiar with the CSA Layer Naming Convention should probably read the description of it before continuing here, since an understanding of the underlying concepts is critical.
The Propylaea model will be divided into layers based on the following criteria:
Most of these categories are self-evident, but others may need some explanation. The beginning date, for instance, will be expressed as four digits with leading zeroes or a minus sign (for B.C.E. dates), as required. Using four digits will make it possible to express any date between 999 B.C.E. and 9999 C.E. Similarly, the ending date is to be expressed with 4 digits, possibly including a minus sign (with 5000 used as an indicator of material that is in place and expected to remain there indefinitely). It is clear that dates will be problematic; many of the changes to the building, especially the small insults caused by gunfire or larger missiles, cannot be precisely dated. As the project moves forward, conventional dates or substitutes (with full documentation) will be adopted to solve such problems.
Between the dates and the block number there will be a character used only to separate the two portions of the name (an underscore) so that users can quickly search for layers by block number (using an AutoCAD® search specification in the form "*_" plus a block number). Of course, the form of the block number will be carefully specified. The point of including the block number is to make it possible to connect the blocks in the model with the drawings that are being scanned for inclusion in the data set.
This system is certainly complex, and it is very demanding for those building the CAD model. It will pay dividends, however, for those using the model in the future, making it possible for them to deal with the model in discrete segments or groups of segments in order to analyze the Propylaea more fully and more accurately.
For other Newsletter articles concerning applications of CAD modeling in archaeology and architectural history the use of electronic media in the humanities, the "CSA CAD Layer Naming Convention," or the Propylaea Project, consult the Subject index.
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Table of Contents for the Spring, 2001 issue of the CSA Newsletter (Vol. XIV, no. 1)
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