3ds Max 2012 Bible - Kelly L. Murdock [99]
The Transform Center flyout consists of three buttons: Use Pivot Point Center, Use Selection Center, and Use Transform Coordinate Center, which are shown in Table 7.3. Each of these buttons alters how the transformations are done. The origin of the Transform Gizmo is always positioned at the center point specified by these buttons.
Pivot Point Center
Pivot points are typically set to the center of an object when the object is first created, but they can be relocated anywhere within the scene including outside of the object. Relocating the pivot point allows you to change the point about which objects are rotated. For example, if you have a car model that you want to position along an incline, moving the pivot point to the bottom of one of the tires allows you to easily line up the car with the incline.
If you select the Use Pivot Point Center button, then the Select and Rotate tool rotates about the pivot point for the selected object, which can be located anywhere in the scene.
Note
Pivot points are discussed in detail in the next section. •
Selection Center
The Use Selection Center button sets the transform center to the center of the selected object or objects regardless of the individual object's pivot point. If multiple objects are selected, then the center is computed to be in the middle of a bounding box that surrounds all the objects.
Transform Coordinate Center
The Transform Coordinate Center button uses the center of the Local Coordinate System. If the View Coordinate System is selected, then all objects are transformed about the center of the viewport grid. If an object is selected as the coordinate system using the Pick option, then all transformations are transformed about that object's center.
When you select the Local Coordinate System, the Use Transform Center button is ignored and objects are transformed about their local axes. If you select multiple objects, then they all transform individually about their local axes. Grouped objects transform about the group axes.
For example, the default pivot point for a Cylinder object is in the middle of the cylinder's base, so if the Transform Center is set to the Use Pivot Point option, then the cylinder rotates about its base pivot point. If the Use Selection Center option is selected, then the cylinder rotates about its center point. If the Use Transform Coordinate Center option is selected for the View Coordinate System, then the cylinder is rotated about the grid origin.
Figure 7.6 shows a simple cylinder object in the Left viewport using the different transform center modes. The left image shows the Pivot Point Center mode, the middle image shows the Selection Center mode with both objects selected, and the right image shows the Transform Coordinate Center mode. For each mode, notice that the Rotate Gizmo is located at different locations.
FIGURE 7.6
The Rotate Gizmo is located in different places, depending on the selected Transform Center mode.
Selecting Axis Constraints
Three-dimensional space consists of three basic directions defined by three axes: X, Y, and Z. If you were to stand on each axis and look at a scene, you would see three separate planes: the XY plane, the YZ plane, and the ZX plane. These planes show only two dimensions at a time and restrict any transformations to the two axes. These planes are visible from the Top, Left, and Front viewports.
By default, the Top, Left, and Front viewports show only a single plane and thereby restrict transformations to that single plane. The Top view constrains movement to the XY plane, the Left or Right side view constrains movement to the YZ plane, and the Front view constrains movement to the ZX plane. This setting is adequate for most modeling purposes, but sometimes you might need to limit the transformations in all the viewports to a single plane. In Max, you can restrict movement to specific transform axes using the