Creating 3D Objects in VectorWorks28 Feb, 2003 By: John E. Wilson
The previous Third Dimension column described the interface and the components of VectorWorks, an $895 CAD program from Nemetschek North America, suitable for both 2D drafting and 3D modeling. VectorWorks runs on computers using either Macintosh or Windows operating systems. For more information on VectorWorks, visit its Web site at www.nemetschek.net. This month's column will explore the program's tools and commands for creating basic 3D objects.
Working in 3D Space
Because the movement of most computer pointing devices is restricted to a plane, you can only specify points that are on a plane, or points on existing 3D objects, with them. (VectorWorks' Constrain to Working Plane must be turned off in order to snap to points on 3D objects that are not on the working plane.) This is a universal problem with 3D modelers, and, like other 3D modelers, VectorWorks has the capability of moving and orienting the working plane anywhere in 3D space. The Set Working Plane tool, for instance, prompts you to pick three points in establishing the origin and the orientation of the working plane, and the View>Rotate Working Plane command displays a dialog box for you to specify the coordinate system axis plus an angle to rotate the Working Plane. (VectorWorks' tools are invoked from buttons in tool palettes, while commands are initiated from screen pull-down menus.) When the Working Plane is not the same as the Ground Plane, its grid lines are colored pink.
VectorWorks automatically rotates the Working Plane to be perpendicular to the viewing direction when you choose one of the six orthographic views from the View>Standard Views menu. For example, when you select the Front view, the Working Plane is on the ground coordinate system's xz plane, and when you select the Right view it is on the yz plane.
As you are working with 3D objects, you can generally best visualize them from a viewing direction that is not one of the six orthographic views. Select one of the six isometric views from View>Standard Views menu to set a viewing direction that has equal angles to all three principle coordinate-system planes, or use the Fly Over tool to dynamically change the viewing direction. Unless you have selected an OpenGL viewing mode (from the View>Rendering>OpenGL menu.), the model usually reverts to a bounding-box display when you use the Fly Over tool. To establish shading with the OpenGL viewing mode, you must create a light with the Light tool (in the 3D Tools palette). The location of the light and its direction are not important for creating working views of you model.
Even though VectorWorks can create some basic 3D objects directly--boxes, spheres, hemispheres, and cones--you will often create 3D objects by pushing (extruding) a profile object into 3D space or by revolving a profile object about an axis. You can, for example, create a column by extruding a circle and a torus by revolving a circle. Generally, these profile objects will be 2D objects, such as a circle or a polyline, created from tools in VectorWorks' 2D Tools palette. A unique property of these 2D objects is that they always appear in their true shape regardless of the current viewpoint. Thus, you can draw a circle in the Top (or Plan) view, and if you then switch to the Front (or even to an Isometric) view, the circle automatically revolves to face the view direction. You will often find the Clip, Add, and Intersect Surface commands, and the Compose command useful in creating 2D profile objects.
You can also use tools in the 3D Tools palette, such as the NURBS Circle tool, to create profile objects. You draw these objects on the current Working Plane, and they are not affected by the viewing direction. You can, for instance, draw a NURBS Circle on the ground plane within an isometric view. However, you can only use these profile objects to create Tapered and Along Path extrusions. You cannot use the Sweep command with them to create a 3D object.
Extruding Profile Objects
The VectorWorks commands for creating extruded 3D objects are in the Model tab of the screen pull-down menu. Of these, Extrude creates a 3D object by pushing a pre-selected 2D object in the viewing direction. In using this command, VectorWorks displays a dialog box for you to enter the extrusion distance, with positive values being toward the viewer. If the 2D object is closed, the two ends of the resulting 3D object will be covered with a surface. Arcs also create a closed 3D object, that is shaped like a pie piece if the arc angle is less than 180 degrees, when they are extruded.
Figure 1. VectorWorks' Multiple Extrude command spreads two or more 2D profile objects along the line of sight and connects them with surfaces.
If you have two or more 2D objects selected, you can use the Multiple Extrude command to create a 3D object. VectorWorks spreads the objects toward the viewer in the order of creation and connects them with surfaces. The extrusion distance you specify is from the first to the last profile. The sides of the resulting 3D object are linear between the profiles, as shown in Figure 1. For best results the profiles should all be the same object type. Using a rectangle and a circle, for example, will result in a 3D object having gaps and holes in its surface. You can, though, include a 2D locus to have the extrusion taper to a point.
The Extrude Along Path command pushes a profile object along a path object. While the profile object must be planar, it can be a 3D object, such as a NURBS circle. The path object, on the other hand, can be either planar or non-planar. You must pre-select the two objects, and then specify which is to serve as the path. VectorWorks then moves the profile so that its centroid is on the end of the path, orients it to be perpendicular to the path, and sweeps it along to the end of the path, as shown in Figure 2.
Figure 2. The Extrude Along Path command of VectorWorks pushes a 2D profile object along a 2D or (as shown here) 3D object.
The Tapered Extrude command works with either 2D or 3D objects, and the profile can even be a non-planar NURBS curve. VectorWorks will display a dialog box for you to specify the extrusion distance and the taper angle. When you specify a positive angle the profile becomes smaller as it is extruded, and when you specify a negative angle it becomes larger.
Sweeping Profile Objects
The Sweep command transforms the space defined by a profile by revolving the profile about an axis into a 3D object. The profile must be a 2D object. The axis is in the y axis direction and it passes through the profile point that is farthest to the left or through a 2D locus. After you select the profile, and if desired, a locus, VectorWorks displays the Create Sweep dialog box for you to enter the parameters of the sweep. These include the angle at which the revolution is to start and the angle through which the profile is to be revolved. Both of these angles are in a plane that is perpendicular to the revolution axis.
You can also create helix-shaped 3D objects with the Sweep command. To do so, use a 2D Locus to establish the centerline of the helix and specify the pitch (the distance between each coil) in the Create Sweep dialog box. The number of coils is controlled by the Arc Angle setting in the Create Sweep dialog box. Thus, to create a spring having two coils, you would set the Arc Angle to 720 degrees.