Using Pivot Points

An object's pivot point is the center about which the object is rotated and scaled and about which most modifiers are applied. Pivot points are created by default when an object is created and are usually created at the center or base of an object. You can move and orient a pivot point in any direction, but repositioning the pivot cannot be animated. Pivot points exist for all objects, whether or not they are part of a hierarchy.

Caution 

Try to set your pivot points before animating any objects in your scene. If you relocate the pivot point after animation keys have been placed, all transformations are modified to use the new pivot point.

Positioning pivot points

To move and orient a pivot point, open the Hierarchy panel in the Command Panel and click the Pivot button. At the top of the Adjust Pivot rollout are three buttons; each button represents a different mode. The Affect Pivot Only mode makes the transformation buttons affect only the pivot point of the current selection. The object does not move. The Affect Object Only mode causes the object to be transformed, but not the pivot point. The Affect Hierarchy Only mode allows an object's links to be moved.

The pivot point is easily identified as the place where the Transform Gizmo is located when the object is selected, as shown in Figure 8.9.

Figure 8.9: The Transform Gizmo is located at the object's pivot point.

Note 

Using the Scale transformation while one of these modes is selected alters the selected object but has no effect on the pivot point or the link.

Aligning pivot points

Below the mode buttons are three more buttons that are used to align the pivot points. These buttons are active only when a mode is selected. These buttons are Center to Object/Pivot, Align to Object/Pivot, and Align to World. The first two buttons switch between Object and Pivot, depending on the mode selected. You may select only one mode at a time. The button turns light blue when selected.

The Center to Object button moves the pivot point so that it is aligned with the object center, and the Center to Pivot button moves the object so it is centered on its own pivot point. The Align to Object/Pivot button rotates the object or pivot point until the object's Local Coordinate System and the pivot point are aligned. The Align to World button rotates either the object or the pivot to the World Coordinate System. For example, if the Affect Object Only mode is selected and the object is separated from the pivot point, clicking the Center to Pivot button moves the object so that its center is on the pivot point.

Under these three alignment buttons is another button labeled Reset Pivot, which you use to reset the pivot point to its original location.

Transform adjustments

The Hierarchy panel of the Command Panel includes another useful rollout labeled Adjust Transform. This rollout includes another mode that you can use with hierarchies of objects. Clicking the Don't Affect Children button places you in a mode where any transformations of a linked hierarchy don't affect the children. Typically, transformations are applied to all linked children of a hierarchy, but this mode disables that.

The Adjust Transform rollout also includes two buttons that allow you to reset the Local Coordinate System and scale percentage. These buttons set the current orientation of an object as the World coordinate or as the 100 percent standard. For example, if you select an object, move it 30 units to the left, and scale it to 200 percent, these values are displayed in the coordinate fields on the status bar. Clicking the Reset Transform and Reset Scale buttons resets these values to 0 and 100 percent.

You use the Reset Scale button to reset the scale values for an object that has been scaled using non-uniform scaling. Non-uniform scaling can cause problems for child objects that inherit this type of scaling, such as shortening the links. The Reset Scale button can remedy these problems by resetting the parent's scaling values. When the scale is reset, you won't see a visible change to the object, but if you open the Scale Transform Type-In dialog box while the scale is being reset, you see the absolute local values being set back to 100 each.

Tip 

If you are using an object that has been non-uniformly scaled, using Reset Scale before the item is linked saves you some headaches if you plan on using modifiers.

Using the Reset XForm utility

You can also reset transform values using the Reset XForm utility. To use this utility, open the Utility panel and click the Reset XForm button, which is one of the default buttons. The benefit of this utility is that you can reset the transform values for multiple objects simultaneously. This happens by applying the XForm modifier to the objects. The rollout for this utility includes only a single button labeled Reset Selected.

Tutorial: A bee buzzing about a flower

By adjusting an object's pivot point, you can control how the object is transformed about the scene. In this example, you animate a bee's flapping wings by repositioning the wings' pivot points. You then reposition the pivot point for the entire bee so it can rotate about the flower object.

To control how a bee rotates about a flower, follow these steps:

1. Open the  Buzzing bee.max file from the Chap 08 directory on the DVD.

   This file includes a bee created from primitives and a flower model created by Zygote Media.

2. Click the bee object to select it, and press Z to zoom in on it in all viewports. Click on the right wing, open the Hierarchy panel, and click on the Affect Pivot Only button. This displays the pivot point in the center of the wing. Drag the wing's pivot point to the right in the Top viewport and then down in the Front viewport until the pivot point is positioned where the wing contacts the body object. Then select the left wing, and move its pivot to the position where it contacts the body object.

3. Click the Auto Key button (or press N) to enable animate mode, and drag the Time Slider to frame 1. Then, with the Select and Rotate button (E), rotate the wing about its Z-axis until it is almost vertical in the Front viewport. Notice how the wing rotates about its new pivot point. Then drag the Time Slider to frame 2, and rotate the wing back to its original position. Click the Auto Key button again (N) to disable key mode.

4. If you want to make these rotations repeat throughout the animation using the Track View, right-click on the wing object and select Curve Editor in the pop-up quadmenu that appears. This opens a Track View with the Rotation tracks selected. In the Track View, select Controller Out-of-Range Types to open the Param Out-of-Range Types dialog box, select the Loop option, and click OK. Then close the Track View.

   CROSS-REF 

   Working with the Track View is beyond the scope of this chapter, but you can find more information on the Track View in Chapter 33, "Working with Function Curves in the Track View."

5. Repeat Steps 3 and 4 for the second wing object. Press the Play Animation button to see both wings flap for the entire animation.

6. Select all parts that make up the bee in the Top viewport, select Group Group, and name the object bee. Then select the bee and the flower in the Left viewport, and press Z to zoom in on them.

7. With the bee group selected, click the Affect Pivot Only button in the Hierarchy panel and move the pivot point to the center of the flower in the Front viewport. Click the Affect Pivot Only button again to disable it.

8. Enable the Auto Key button (N) again, and drag to frame 35. With the Select and Rotate button (E), rotate the bee in the Top viewport a third of the way around the flower. Drag the Time Slider to frame 70, and rotate the bee another third of the way. With the Time Slider at frame 100, complete the rotation. Click the Auto Key button again to display key mode.

9. Click the Play button (/) to see the final rotating bee.

Figure 8.10 shows the bee as it moves around the flower where its pivot point is located.

Figure 8.10: By moving the pivot point of the bee, you can control how it spins about the flower.