Encoding geometry

Abstract

Before considering the large range of facilities provided by CAD software we will look at the way the computer represents the drawing in its memory. We can divide the information in a design into two types: numerical data specifying lengths etc and qualitative information such as notes, identifiers and descriptors of various kinds. All information has to be held in the memory in the form of a list of integers for that is how the memory is organised. As mentioned in “An introduction to computers” on page 5, anything can be represented by a number. All that is needed is a conversion table to convert between the number and the description the human being uses. The software therefore codes all qualitative information into lists of numbers using whatever conversion tables the programmer might invent for his own convenience. Most of it will be kept as text for which there is an international standard conversion code.