UNDERSTANDING THE UCS

In this Lesson you are going to learn how to manipulate the UCS Origin to make constructing 3D models easy and accurate.

World Coordinate System vs. User Coordinate System

All objects in a drawing are defined with XYZ coordinates measured from the 0, 0, 0 Origin. This coordinate system is fixed and is referred to as the World Coordinate System (WCS). When you first launch AutoCAD, the WCS icon is in the lower left corner of the screen. (An easy way to return to WCS is: Type UCS .)

On the other hand, the User Coordinate Sytem (UCS) can move its Origin to any location. (This is a procedure with which you are familiar, referred to as moving the Origin .)

Why move the UCS Origin?

Objects that are drawn will always be parallel to the XY plane. (Unless you type a Z coordinate) So it is necessary to define which plane you want to work on. You define the plane by moving the UCS origin to a surface.

Let me give you a few examples and maybe it will become clear.

Example 1:

This wedge was drawn using L, W, H. When you entered the L, W and H how did AutoCAD know to draw its base parallel to the XY plane? Because all objects are drawn parallel to the XY plane unless you enter a Z coordinate. Length is always in the X axis, Width is always in the Y axis...