Introduction to AutoCAD 3D

I want to mention some useful information about basic 3D in AutoCAD in today’s article. I usually choose conceptual subjects of AutoCAD because I think once you learn those, there is nothing difficult in drawing at all.

I have discussed that objects are drawn in model space and there is a user coordinate system (UCS) icon at the origin (x,y=0,0) of this space. To continue with today’s subject, I want to talk about the UCS icon first.
Actually, you draw in 3D model space in AutoCAD without be aware of. There are two reasons for you to recognize it 2D. The first one is that you are looking the space from the top, and this view mode in AutoCAD is known as ‘Plan View’. It is not important for now but the other reason is that you are drawing 2D objects anyway. ‘What is the relation between the stuff you mentioned and the UCS?’, I suppose you are asking. Yet, this is the point UCS icon shows up. When you look at the bottom left on the screen, you will see one of the two icons seen in the figure below.

Figure 1 and 2
They both are the same. One of them is the 2D icon used in older versions and the other is 3D icon used in latest versions. Both designate the VIEWPOINT, the current coordinate system and the positive directions of ‘X’ and ‘Y’ axes. The icon will be the same with the one in figure unless you set something differently. If you are a former AutoCAD user and want your old icon back, you can select ‘2D Icon’ option from the properties tab of the UCSICON command (Figure 3). The untold options of the window are surely going to be discussed in future articles.
Figure 3
Unless you change something, UCS icon is located at the origin point where X and Y values are both equal to zero. Besides, it is also the world coordinate system (WCS). That is enough with the UCS icon; let me go on with the 3D concepts.

ViewPoint and UCS (User Coordinate System):
The default coordinate system is WCS (World Coordinate System) and default viewpoint is ‘Plan View’ in AutoCAD. Moreover, primitive commands like LINE, PLINE, CIRCLE and ARC forms 2D objects since you are drawing in 2D mode. So, the objects that you draw are placed on XY plane. To draw in 3D, you have to change your viewpoint and get used to utilizing the UCS effectively.

To Change the Viewpoint:
VPOINT command is used for chancing the viewpoints. You will access the dialog box seen in Figure 4 if you type ’VP’ into the command line or browse ‘View/3D Views/ViewPoint Presets…’ in the menu.
Figure 4 (You can also use NAVCUBE from now on)
As you can see, WCS is defined like a view angle that you are looking to the XY Plane form the top (90 degrees) and the orientation of the X axis is 270° in the plane. Changing the values as 225 for ‘From X Axis’ and 25-30 degrees for ‘From XY Plane’ also changes the UCS icon (Figure 5).
Figure 5
Now, the model space is in 3D form and you are ready to draw in 3D. Squares and circles are the best recognizable 3D objects. Let us practice with a simple example to better understand the ‘Viewpoint’ and ‘UCS Icon’ concepts.

Step.1 Draw a square on the ground:

Command: REC 30,30 @40,40
Step.2 Draw another square that is perpendicular to the previous one by chancing the UCS.

Command: UCS x 90
As you enter the command, UCS icon rotates 90° around X axis and the cursor plane is being changed.
Figure 6
Step.3 Draw another square

Command: REC 30,30 @40,40
The command is same with the first one but the coordinate system is different (Perpendicular to the old one). So our new square is going to be perpendicular to the old one.
Figure 7
Actually the object you drew is a 2D one but with a change in the coordinate system, AutoCAD performs the commands in the new defined plane. You can examine the same example with rotating the coordinate system around Y axis. The squares can be copied perpendicularly by passing to the WCS. You should check the commands like MOVE or ROTATE in different coordinate systems.

Do not force yourself to draw 3D objects immediately. Instead, check the 2D objects with chancing the UCS. If you try to switch 3D swiftly you may be disappointed.

I tried to mention the main concepts of 3D for freshmen and beginners. I will discuss forming 3D objects, solid modeling, advanced UCS usage and viewpoints in my upcoming articles.

I am looking forward to hearing your comments.