16
AutoCAD and Its Applications—Advanced
Using Rectangular 3D Coordinates Using Rectangular 3D Coordinates
In two-dimensional drawing, you see one plane defi by two dimensions. These fined
dimensions are usually located on the X and Y axes and what you see is the XY plane.
However, in 3D drawing, another coordinate axis—the Z axis—is added. This results
in two additional planes—the XZ plane and the YZ plane. If you are looking at a stan-
dard AutoCAD screen after AutoCAD is launched using the
acad.dwt
template, the
positive Z axis comes directly out of the screen toward you. AutoCAD can only draw
lines in 3D if it knows the X, Y, and Z coordinate values of each point on the object. For
2D drawing, only two of the three coordinates (X and Y) are needed.
Compare the 2D and 3D coordinate systems shown in Figure 1-1. Notice that the
positive values of Z in the 3D coordinate system come up from the XY plane. In a new
drawing based on the
acad.dwt
template, consider the surface of your computer screen
as the XY plane. Anything behind the screen is negative Z and anything in front of the
screen is positive Z.
The object in Figure 1-2A is a 2D drawing showing the top view of an object. The
XY coordinate values of the origin and each point are shown. Think of the object as
being drawn directly on the surface of your computer screen. However, this is actually
a 3D object. When displayed in a pictorial view, the Z coordinates can be seen. Notice in
Figure 1-2B that the first two values of each coordinate match the X and Y values of the fi
2D view. Three-dimensional coordinates are always expressed as (X,Y,Z). The 3D object
was drawn using positive Z coordinates. Therefore, the object comes out of your computer
Figure 1-1.
A comparison of 2D and 3D coordinate systems.
Origin
2D Coordinates 3D Coordinates
Origin
+Y
+Y
+Z
+X
+X
Figure 1-2.
A—The points making up a 2D object require only two coordinates. B—Each point of a 3D
object must have an X, Y, and Z value. Notice that the first two coordinates (X and Y) are the
same for each endpoint of a vertical line.
A B
0,4 6,4
0,4,1
6,4,1
6,4,0
6,2,0
4,2,0
4,0,0
2,0,0
0,0,0
2,0,1
4,0,1
0,2,0
0,2,1
2,2,1
4,2,1
6,2,1
6,2 4,2 2,2 0,2
0,0 2,0 4,0