156 Exploring Drafting
Basic CAD System
Functions
One of the main benefi ts of CAD drafting
is the added productivity and effi ciency made
possible by tools in the software. Many of these
tools are designed to automate the common
tasks associated with traditional (manual)
drafting. There are a number of basic features
and functions common to most types of CAD
software. These include coordinate systems,
drawing aids, layers, linetypes, and blocks.
These features are discussed in the following
sections.
Coordinate Systems
As previously discussed, objects in a
CAD drawing are defi ned with coordinates.
Coordinates are points representing units of
real measurement from a fi xed point. Most
CAD programs provide a basic coordinate
system and the ability to create user-definedfi
coordinate systems. The most basic coordi-
nate system in a typical program is the world
coordinate system. This system is based on the
Cartesian coordinate system. In this system,
objects are defi ned by coordinates along the
X axis (horizontal axis), Y axis (vertical axis),
and Z axis (the axis projecting perpendicular
from the XY plane). Coordinates are located
in relation to the 0,0,0 origin. See Figure 7-6.
The horizontal and vertical axes of the
Cartesian coordinate system divide the XY
drawing plane into four quadrants. See
Figure 7-7. Coordinates are entered as posi-
tive or negative, depending on the location
from the origin. Referring to Figure 7-7,
the coordinate (2,2) is located in the upper-
right quadrant. This quadrant has positive
X coordinates and positive Y coordinates.
The coordinate (4,–3) is located in the lower-
right quadrant. This quadrant has positive
X coordinates and negative Y coordinates.
The coordinate (–6,8) is located in the upper-
left quadrant. This quadrant has negative X
coordinates and positive Y coordinates. The
(–X,+Y)
(–6,8)
Y axis
(+X,+Y)
(2,2) X axis
(4,–3)
Origin
(0,0)
(–3,–5)
(–X,–Y) (+X,–Y)
Figure 7-7 The XY axes of the Cartesian coordinate
system divide the drawing plane into four quadrants.
Coordinates have positive or negative X and Y values.
Z
axis
Y axis
Y
X
Origin (0,0,0)
Z
X axis
Figure 7-6 In the Cartesian coordinate system,
coordinates establish points of measurement along
the X, Y, and Z axes in relation to the 0,0,0 origin.
coordinate (–3,–5) is located in the lower-left
quadrant. This quadrant has negative X coor-
dinates and negative Y coordinates.