CAD - computer aided design (Archaeology)

Originally developed for architectural and engineering purposes, CAD (Computer-Aided Design) software is now used in a multitude of disciplines and integrates seamlessly with the archaeological point data that may be acquired from a variety of sources including Total Station surveys and GPS (Global Positioning System) readings. CAD packages enable the user to create 2D and 3D vector-based drawings and work with a coordinate referencing system, x and y for position and z for height. The coordinates can refer simply to the drawing itself or can reference either to an excavation site plan or, perhaps in the case of a regional survey, might reference National Grid coordinates or the UTM (Universal Transverse Mercator).

Drawings can consist of layers of information which can be edited and manipulated either separately or together adding functionality to the pre-digital technique of pin-bar drafting (using transparencies to overlay a base sheet using registration pins to ensure accuracy). An extensive range of functionality allows entities within the drawing to be scaled, rotated, distorted, skewed, re-aligned etc., and line types and the rendition of objects as wire frames or solid models can be selected. Raster images can also be imported to be used either as background or as textural elements within the vector-based environment.

Where CAD and GIS packages start to overlap is the ability not only to store CAD objects in libraries for reuse in other contexts, but also to store attribute information about the objects separately, in a database if needs be. Some CAD packages also include their own programming and control language allowing application-specific front end menus to be built. Commercial systems like AutoCAD and SolidWorks give the user enormous expressive power to visualize 2D and 3D models but for those with more modest requirements and limited budgets, QCAD may suffice for 2D modelling whilst the freely downloadable Google Sketchup is very user-friendly and enables 3D models to be developed very rapidly.

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