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Object Hierarchies
An object hierarchy lets you create relationships between objects.
A hierarchy adds structure to the objects in your scene. This can make arranging and animating objects much easier. When you're arranging objects, a hierarchy can make positioning and rotating easier since you can transform an entire hierarchy all at once instead of separately. The same is true for animating. You can quickly create motion animations by changing the position of a parent object, since all its children will move with it.
Hierarchies can be created by either grouping or linking objects.
Grouping vs. Linking
Both grouping and linking let you create functional or spatial relationships between objects. The difference is how the objects within each hierarchy work.
Within a group all the objects act as one. When you resize a group of objects, you are resizing all objects in the group simultaneously. This type of hierarchy is good for creating complex objects with static parts, like a tree or a large terrain.
Within a linked hierarchy objects behave differently depending on which object within the hierarchy is being transformed. Any transformation you apply to the parent object is applied to all its children. However, transformations applied to a child object do not affect the parent. This type of hierarchy is good for creating objects that have moving parts or animating two objects simultaneously.
You can control exactly which transformations are applied to a child object using the options on the Linking tab in the Object Attributes dialog.
Hierarchical Structure
A hierarchical structure consists of a parent object or objects and its descendants. In the case of linking, the parent object is at the top of the hierarchy and its children are below it. Children in the hierarchy can also have children creating a branched hierarchy.
In a hierarchy created using links, the parent object is the primary object in the link. The children are any objects linked to the parent. If you have multiple linked objects in a hierarchy, the parent object at the top of the hierarchy is the parent object in the first link you created.
In this link hierarchy, the parent object has one child and that child has two children one of which also has a child. So if you were to transform this hierarchy, any operation you perform on the Parent at the top of the hierarchy is applied to all its children.
In a hierarchy created using groups, the parent object is the group. All the objects within the group are the children. If you have multiple groups within a group, the parent object is the final group you create.
In this group hierarchy the parent group has four children one of which is a group that contains three children. If you were to transform this hierarchy, any operation you perform on the parent group would be applied to all the children.
A hierarchy can be made up of both linked and grouped objects. One way of creating this type of hierarchy is by grouping the parent objects from different link hierarchies together. In this case, the final group you create would become the parent object of the hierarchy.
You cannot create a group using a child object. Only parent objects can be part of a group. When the parent is in a group all its children are also part of the group since they must follow the parent.
You could also create a hierarchy where a group is linked to a parent object. In this case, the parent object of the hierarchy would be the parent from the first link you created.
In this hierarchy the parent object is a group that has four children one of which is the parent object of a link hierarchy that has two children.
Viewing Object Hierarchies
The Hierarchy List area of the Advanced Motion Lab lets you see a list of all the objects in your scene. Object hierarchies are indicated by indents. A parent object is listed at the far left of the area; its children appear indented beneath it.
The name of an object that appears in the Hierarchy List can be set using the Object Attributes dialog. If no name is set, a default name is used (for example Sphere 1).
These names are unique for each item in the scene, and are not reused regardless of the number of objects you create or whether the object has been deleted.
To view a listing of the hierarchy:
1 In the Working window, make sure there are no objects selected. This will let you see all the hierarchies in your scene.
2 Click the Advanced Motion Lab button at the bottom of the window. The Advanced Motion Lab appears.
The Hierarchy List area, located along the bottom-left side of the lab, displays all the hierarchies in your scene.
Expanding and Collapsing a Hierarchy
The arrow buttons next to an object's listing indicate whether the hierarchy is expanded or collapsed. A collapsed hierarchy shows only the parent objects in the hierarchy. An expanded hierarchy shows a listing for all the children.
To expand/collapse a hierarchy listing:
Click the arrow again to collapse the listing.
Linking Objects
When you link two objects, you connect them in a Parent-Child link.
In a parent-child link, the parent controls the actions of the child. This means that when the parent object moves, so does the child object. However, when the child object moves, the parent object does not.
A child object will start its movement from its original position and always maintain a constant distance from the parent. The distance is determined by the original positions of the objects before they were linked.
The movement of the child object depends entirely on the type of transformations you apply to the parent object.
To link objects in the Working window:
1 Select the object you want to set as the child object. A series of icons appear next to the object's bounding box.
2 Click the Link icon and drag the linking line to the object you want to use as the parent object.
You cannot create a link where the parent object is the child of its own child object (i.e. a loop).
To link objects using the Object Attributes dialog:
1 Select the object you want to use as the child object.
2 Click the A icon that appears next to the object's bounding box. The Object Attributes dialog appears.
4 Click the Object Parent Name menu and choose the name of the object you want to use as the parent object.
5 Click the OK icon to link the two objects.
To break a link:
2 Click the A icon that appears next to the object's bounding box. The Object Attributes dialog appears.
4 Click the Object Parent Name menu and choose None.
5 Click the OK icon to unlink the two objects.
Linking Options
Using the options available in the Linking tab on the Object Attributes dialog, you can control which parent object transformations are applied to child objects and how objects are constrained when they're linked to a path.
Parent to Child Transformations Options
Once you've created a link, you can determine exactly which transformations applied to the parent will affect the child.
To set which parent object transformations are applied to a child:
1 Display the Object Attributes dialog.
3 Disable the buttons for the transformation you don't want applied to the child.
Geometric Path Linking Options
A Geometric path is an object that acts like a track for controlling the motion of objects. Normally, when you link an object to a Geometric Path, it is constrained to the path. However, using the linking options in the dialog you can disable or enable constraining.
When an object is constrained to the path, it can only move along the path. When it's not constrained it acts like a regular child of the path. Its movement is not constrained to the path.
The options in this dialog also let you set where on the path an object begins its motion.
For more information about geometric paths, refer to "Creating Geometric Paths".
To constrain/unconstrain an object to a geometric path:
1 Select an object linked to a geometric path.
2 Display the Object Attributes dialog.
4 Enable the Constrain to path button to constrain the object to the path.
To set where the object sits on the path:
1 Select an object linked to a geometric path.
2 Display the Object Attributes dialog.
4 Enter a percentage in the Position field.
100% places the object at the end of the path, and 0% places it at the beginning.
Grouping Objects
As your scene becomes more complex, you'll need to group objects. Grouping lets you control a set of objects as a single unit. When you perform a transformation on a group, all the objects are equally affected. If you scale a group, all the objects change size, or if you rotate a group, all the objects rotate around a single axis.
Your choice of objects to place in a group depends on how you want to organize your scene. You may want to group the objects that comprise more complex objects, like the walls and turrets of a castle.
You can also create groups to maintain the spatial relationships between objects as you transform them.
You can place as many objects as you like in your group. You can even nest groups within groups. Nesting can be an easy way of managing more complex scenes.
Groups are essential to creating Boolean objects. Boolean operations will not work unless the objects are part of a group. Refer to "Boolean Operations" for more on Boolean objects.
You cannot create a group using a child object. If a child object is part of your selection the "G" icon will not appear.
To create a new group:
1 Select all the objects you want to group.
2 Choose Objects menu>Group Objects, or press Command/Ctrl+G.
You can also click the G button next to the selected objects' bounding box.
To select objects within a group:
1 Hold down Control/Ctrl and click on an object inside the group bounding box.
2 Select the object you want from the menu.
Families
Families are a way of creating "logical groups." Unlike regular groups, families are not treated as a single unit with regards to transformations. Families help you keep track of elements in your scene, and can be used for selection purposes. For example, you can put all the elements that make up the background of your scene in to one family, all the items with a particular material in another, all trees in another and so on.
Each family has a different object color. The color appears only when the object is not selected, since a selected object's bounding box appears red.
To create a new family:
1 Select all the objects you want in the family.
2 Click the dark gray box next to the selection's bounding box. The Family dialog appears.
3 Click on a color. The color is applied to the wireframes of all the objects in the family.
4 You adjust these colors by dragging the rectangular color swatch at the bottom of the dialog. Avoid using black or white since they are difficult to see, or red since it's the color of a selected object.
5 Enter a name for the family in the text field.
To select a family:
1 If the Animation controls are visible at the bottom of the Bryce window, click the Time/ Selection Palette toggle to display the Selection palette.
2 Click the Family button and choose the name of the family you want to select from the menu.
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