### From Draftsperson.net

Revision as of 14:02, 26 June 2006;

view current revision←Older revision |

Newer revision→
Written by MikeD

One of the hardest things I found when learning about geometry and computer graphics was how to 'see' a rotation matrix and how they are used, they are a handy thing to have and understand in your programming toolkit for AutoCad also. I won't delve to deep into matrices or calculations, what I hope to achieve in this article is to expose a simple way for you to 'see' a rotation matrix, when I read an article on basic trig it all fell into place so that's where we'll start.

## Our use of Trigonometry

Without going into the nitty gritty of it, trig is basically about triangles, 'right' triangles to be exact and the thing they didn't teach us at school (our school anyway) was that the basic elements of trig, being sine, cosine and tangent, were all based around angles **within a unit circle!** This is a very important concept to remember and will be used later, so pay attention ;)
(A unit circle is simply a circle with a radius of 1, a single unit.

Figure 01. Showing the elements involved in trigonometry calculations.