Introduction to 3D Design using AutoCAD

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(For more resources related to this topic, see here.)

The Z coordinate

3D is all about the third Z coordinate. In 2D, we only care for the X and Y axes, but never used the Z axis. And most of the time, we don’t even use coordinates, just the top-twenty AutoCAD commands, the Ortho tool, and so on. But in 3D, the correct use of coordinates can substantially accelerate our work. We will first briefly cover how to introduce points by coordinates and how to extrapolate to the third dimension.

Absolute coordinates

The location of all entities in AutoCAD is related to a coordinate system. Any coordinate system is characterized by an origin and positive directions for the X and Y axes. The Z axis is obtained directly from the X and Y axes by the right-hand rule: if we rotate the right hand from the X axis to the Y axis, the thumb indicates the positive Z direction.

Picture that when prompting for a point; besides specifying it in the drawing area with a pointing device such as a mouse, we can enter coordinates using the keyboard.

The format for the absolute Cartesian coordinates related to the origin is defined by the values of the three orthogonal coordinates, namely, X, Y, and Z, separated by commas:

X coordinate, Y coordinate, Z coordinate

The Z coordinate can be omitted.

For instance, if we define a point with the absolute coordinates 30, 20, and 10, this means 30 absolute is in the X direction, 20 is in the Y direction, and 10 is in the Z direction.

Relative coordinates

Frequently, we want to specify a point in the coordinates, but one that is related to the previous point. The format for the relative Cartesian coordinates is defined by the symbol AT (@), followed by increment values in the three directions, separated by commas:

@X increment, Y increment, Z increment

Of course, one or more increments can be 0. The Z increment can be omitted.

For instance, if we define a point with relative coordinates, @0,20,10, this means in relation to the previous point, 0 is in X, 20 is in Y, and 10 is in Z directions.

Point filters

When we want to specify a point but decompose it step-by-step, that is, separate its coordinates based on different locations, we may use filters. When prompting for a point, we access filters by digitizing the X, Y, or Z axes for individual coordinates, or XY, YZ, or ZX for pairs of coordinates. Another way is from the osnap menu, CTRL + mouse right-click, and then Point Filters. AutoCAD requests for the remaining coordinates until the completion of point definition.

Imagine that we want to specify a point, for instance, the center of a circle, where its X coordinate is given by the midpoint of an edge, its y coordinate is the midpoint of another edge, and finally its Z coordinate is any point on a top face. Assuming that Midpoint osnap is predefined, the dialog should be:

Command: CIRCLE
Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: .X
of midpoint of edge
(need YZ): .Y
of midpoint of edge
(need Z): any point on top face
Specify radius of circle or [Diameter]: value

Workspaces

AutoCAD comes with several workspaces. It’s up to each of us to choose a workspace based on a classic environment or the ribbon. To change workspaces, we can pick the workspace switching button on the status bar:

There are other processes for acceding this command such as the workspaces list on the Quick Access Toolbar (title bar), the Workspaces toolbar, or by digitizing WSCURRENT, but the access shown is consistent among all versions and always available.

Classic environment

The classic environment is based on the toolbars and the menu bar and doesn’t use the ribbon. AutoCAD comes with AutoCAD Classic workspace, but it’s very simple to adapt and view the suitable toolbars for 3D.

The advantages of using this environment are speed and consistency. To show another toolbar, we right-click over any toolbar and choose it. Typically, we want to have the following toolbars visible besides Standard and Layers: Layers II, Modeling, Solid Editing, and Render:

Ribbon environment

Since the 2009 version, AutoCAD also allows for a ribbon-based environment. Normally, this environment uses neither toolbars nor the menu bar. AutoCAD comes with two ribbon workspaces, namely, 3D Basics and 3D Modeling; the first being less useful than the second.

The advantages are that we have consistency with other software, commands are divided into panels and tabs, the ribbon can be collapsed to a single line, and it includes some commands not available on the toolbars. The disadvantage is that as it’s a dynamic environment, we frequently have to activate other panels to access commands and some important commands and functions are not always visible:

When modeling in 3D, the layers list visibility is almost mandatory. We may add this list to the Quick Access Toolbar by applying the CUI command or by right-clicking above the command icon we want to add. Another way is to pull the Layers panel to the drawing area, thus making it permanently visible.

Layers, transparency, and other properties

When we are modeling in AutoCAD, the ability to control object properties is essential. After some hours spent on a new 3D model, we can have hundreds of objects that overlap and obscure the model’s visibility. Here are the most important properties.

Layers

If a correct layers application is fundamental in 2D, in 3D it assumes extreme importance. Each type of 3D object should be in a proper layer, thus allowing us to control its properties:

  • Name: A good piece of advice is to not mix 2D with 3D objects in the same layers. So, layers for 3D objects must be easily identified, for instance, by adding a 3D prefix.

  • Freeze/Thaw: In 3D, the density of screen information can be huge. So freezing and unfreezing layers is a permanent process. It’s better to freeze the layers than to turn off because objects on frozen layers are not processed (for instance, regenerating or counting for ZOOM Extents), thus accelerating the 3D process.

  • Lock/Unlock: It’s quite annoying to notice that at an advanced phase of our project, our walls moved and caused several errors. If we need that information visible, the best way to avoid these errors is to lock layers.

  • Color: A good and logical color palette assigned to our layers can improve our understanding while modeling.

  • Transparency: If we want to see through walls or other objects at the creation process, we may give a value between 0 and 90 percent to the layers transparency.

Last but not least, the best and the easiest process to assign rendering materials to objects is by layer, so another good point is to apply a correct and detailed layer scheme.

Transparency

Transparency, as a property for layers or for objects, has been available since Version 2011. Besides its utility for layers, it can also be applied directly to objects. For instance, we may have a layer called 3D-SLAB and just want to see through the upper slab. We can change the objects’ transparency with PROPERTIES (Ctrl + 1).

To see transparencies in the drawing area, the TPY button (on the status bar) must be on.

Visibility

Another recent improvement in AutoCAD is the ability to hide or to isolate objects without changing layer properties.

We select the objects to hide or to isolate (all objects not selected are hidden) and right-click on them. On the cursor menu, we choose Isolate and then:

  • Isolate Objects: All objects not selected are invisible, using the ISOLATEOBJECTS command

  • Hide Objects: The selected objects are invisible, using the HIDEOBJECTS command

  • End Object Isolation: All objects are turned on, using the UNISOLATEOBJECTS command.

There is a small lamp icon on the status bar, the second icon from the right. If the lamp is red, it means that there are hidden objects; if it is yellow, all objects are visible:

Shown on the following image is the application of transparency and hide objects to the left wall and the upper slab:

Auxiliary tools

AutoCAD software is very precise and the correct application of these auxiliary tools is a key factor for good projects. All users should be familiar with at least Ortho and Osnap tools. Following is the application of auxiliary tools in 3D projects complemented with the first exercise.

OSNAP, ORTHO, POLAR, and OTRACK auxiliary tools

Let’s start with object snapping, probably the most frequently used tool for precision. Every time AutoCAD prompts for a point, we can access predefined object snaps (also known as osnaps) if the OSNAP button on the status bar is on. To change it, we only have to click on the OSNAP button or press F3. If we want an individual osnap, we can, among other ways, digitize the first three letters (for instance, MID for midpoint) or use the osnap menu (CTRL + right-click). Osnaps work everywhere in 3D (which is great) and is especially useful is the Extension osnap mode, which allows you to specify a point with a distance in the direction of any edge.

But what if we want to specify the projection of 3D points onto the working XY plane? Easy! If the OSNAPZ variable is set to 1, all specified points are projected onto the plane. This variable is not saved and 0 is assigned as the initial value.

More great news is that ORTHO (F8) and POLAR (F10) work in 3D. That is, we can specify points by directing the cursor along the Z axis and assign distances. Lots of @ spared, no?

OTRACK (F11), used to derive points from predefined osnaps, also works along the Z-axis direction. We pause over an osnap and can assign a distance along a specific direction or just obtain a crossing:

3DOsnap tool

Starting with Version 2011, AutoCAD allows you to specify 3D object snaps. Also, here we can access predefined 3D osnaps keeping 3DOSNAP (F4) on, or we can access them individually. There are osnaps for vertices, midpoints on edges, centers of faces, knots (spline points), points perpendicular to faces, and points nearest to faces.

Exercise 1.1

Using the LINE command, coordinates, and auxiliary tools, let’s create a cabinet skeleton. All dimensions are in meters and we start from the lower-left corner. The ORTHO or POLAR button must be on and the OTRACK and OSNAP buttons with Endpoint and Midpoint predefined.

As in 2D, rotating the wheel mouse forward, we zoom in; rotating the wheel backward, we zoom out; all related to cursor position. To automatically orbit around the model, we hold down SHIFT and the wheel simultaneously. The cursor changes to two small ellipses and then we drag the mouse to orbit around the model. Visualization is the subject of the next article

  • We run the LINE command at any point, block direction X (POLAR or ORTHO) and assign the distance:

    Command: LINE
    Specify first point: any point
    Specify next point or [Undo]: 0.6

  • We block the Z direction and assign the distance:

    Specify next point or [Undo]: 0.7

  • The best way to specify this point is with relative coordinates:

    Specify next point or [Close/Undo]: @-0.3,0,0.4

  • We block the Z direction and assign the distance:

    Specify next point or [Close/Undo]: 0.7

  • The best way to close the left polygon is to pause over the first point, move the cursor up to find the crossing, with Polar or Ortho coming from the last point, and apply Close option to close the polygon:

    Specify next point or [Close/Undo]: point with OTRACK
    Specify next point or [Close/Undo]: C

  • We copy all lines 1 meter in the Y direction:

    Command: COPY
    Select objects: Specify opposite corner: 6 found
    Select objects: Enter
    Current settings: Copy mode = Multiple
    Specify base point or [Displacement/mOde] <Displacement>: point
    Specify second point or [Array] <use first point as displacement>:
    1
    Specify second point or [Array/Exit/Undo] <Exit>: Enter

  • We complete the cabinet skeleton by drawing lines between endpoints

    Command: LINE

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