To draw accurately in an AutoCAD 2 Dimensional (2D) drawing, you must supply locations by entering XY coordinates. The 2D coordinates are based on the Cartesian Coordinates System. The Cartesian Coordinate System consists of two numbered lines crossing perpendicular to each other at their zero values. The horizontal axis is called the X-axis, and the vertical axis is called the Y-axis as shown in Figure 4-1. This allows you to assign a value to each location on a plane. Each coordinate location consists of a pair of numbers, the first of which is the X-coordinate and the second is the Y-coordinate, written (X,Y). For example, (3,4) is a location 3 units to the right 4 units up from X0,Y0.
Cartesian coordinate can be entered into AutoCAD as either Absolute or Relative coordinates.
Absolute Cartesian Coordinates
Absolute Cartesian Coordinated are
always referenced to the absolute origin
0,0. For example: 3,4
Relative Cartesian Coordinates
Relative Cartesian Coordinated are incremental to the last input point. To indicate to
AutoCAD that it is a relative coordinate you are referring to, enter an @ before the
coordinate. For example @2,6.
AutoCAD has been programmed to understand the @ symbol as meaning
“The Last Point”. AutoCAD always remembers the last point entered by
the user so when the @ is used, for example: @2,4, that means to
AutoCAD “from the last point entered go 2 units in the X direction and 4
units in the Y direction”. The @ is used in many different ways as you will
see as you work your way through the modules.
Example drawings to practice Absolute and relative co-ordinate systems:
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