Computer aided design (CAD) systems have proved to be a very valuable toll widely used in industry. These systems are often expensive both from the hardware and software point of view. As such first hand training becomes an expensive proportion especially in an environment where training is the main goal and production a secondary or a minor goal. Such is the case in the educational institutions. This paper describes a two-dimensional Computer Aided Design Tutorial System (CADETS) modelled after Unigraphics I. Written in APL, the system does not demand any knowledge of APL for the user. An IBM 3279 colour graphics terminal is used as a graphics input as well as output device. The screen is divided into five windows. The main, and the largest, window is used for graphics; the others are used for user communication. Menus are used extensively to generate, modify and manipulate the display. Within CADETS, there are currently eleven ways to create a point, thirteen ways to create a line segment, ten ways to specify a circular arc and several functions to generate common geometric objects such as triangles, rectangles, polygons, etc. Once created, the user may edit the graphics model by deleting geometric entities either individually or in a group. Line segments may be extended or trimmed to specified boundaries, constrained to intersect at a corner, etc. Arcs may be extended or truncated so that they would be bound by specified angles or points or lines which intersect them. The visual attributes of any entity may be changed. The user can also control the view area and scale of model thus providing a pan and zoom capability to concentrate on selected areas of the display. An interface has been provided to produce a hardcopy on a variety of devices. The system has been used by several users including high school students who were unaware of even the existence of APL. The system requires minimal investment on hardware as well as software compared to sophisticated expensive systems, yet provides tools for teaching several fundamental CAD techniques. Plans are underway to enhance 2-D capabilities, incorporate other inexpensive graphics devices and include 3-D graphics.
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