Parametric Design is a method of correlating dimensions and variables with geometry whereas when the values change, the part changes as well. Parametric design is the latest development in CAD software, and refers to the inclusion of parametric data embedded within 3D objects (i.e., all the parameters, such a s height, depth, thicknesses, weight, and even attributes such as model numbers and materials).

Parametric design is, in a sense, a rather restricted term; it implies the use of parameters to define a form when what is actually in play is the use of relations. It should also be noted that, from an elementary point of view, there is not a clear boundary between what can be called parametric design and what is currently called computer aided drafting or modelling. In these cases, forms are created by combining basic entities that are inserted in the model after a basic template, which includes their "proper parameters", is filled. A line, for example, is an entity that becomes part of a model once two parameters, its length and its direction, are specified. A polyline is a set of lines joined at their vertices whose position parameters must also be specified when it is created. A prismatic meshed volume is inserted in a model through four parameters, its location, length, width and height. Besides this, we can also define "blocks" (AutoCad), "cells" (Microstation) "symbols" or "components" (other systems) that combine and keep together with different overall values these primitive forms. There are also, in current CAD systems, tools that allow us to make some modifications a posteriori on these primitive entities. However this does not work for complex elements where we want relations to be maintained while modifying their parts independently. We can define a metal window as a block but, if we change the scale at the moment of insertion, frame sections will change in the same proportion as the overall magnitude and we will not be able to keep a standard frame with different opening dimensions. But we can still define a procedure, through some programming language like AutoLisp, in such a way that only the relations are specified and the adequate dimensions are defined only at the moment of insertion in the model. This is already parametric design in a literal and fundamental sense. And it is, obviously, of interest in the case of architecture due to the fact that a very important number of building elements can be grouped in families that tend spontaneously to be parameterized. And, if this can be done in a satisfactory way it can save a lot of time and computer memory and will also help the management of these elements. As the notion of family is important in parametric design we can define it formally: a set of elements that only differ in the dimension of their parts. To describe a family, to elaborate a primary design of a family, we only need two things; a topological description specifying the parts that constitute it and the relations they maintain with each other and a dimensional scheme specifying priorities and dimensional constraints. In this way we can define an abstract collection of elements and insert them in our models. This is good for a start, but what happens if after the element is inserted we want to modify it? This is where parametric design, in a promising way, properly started, in CAD/CAM, a few years ago in relation with the fundamental notion of constraint. What we would want is the ability to spontaneously change elements in a 2 or 3- dimensional model, and then have their respective connected parts change to correspond.

More to follow....