Understanding hierarchies

- [Instructor] In chapter 10 we'll look at hierarchies or connecting objects together, especially for animation. You will need to have objects connected to one another. For example we've got our little artist mannequin here and we can pose that mannequin by rotating the various parts. If I select his shoulder for example, I can rotate that. Before I do I just want to make it a little bit easier to see by disabling these selection brackets. That's the J key on the keyboard. And also turning on the selection highlighting with edged faces.

A selected object can be displayed in an edged faces mode. That's done from the view port menu here. The right most entry on that menu; click on that. go down to display selected and enable display selected with edged faces, and that way it's a little easier to see what we've selected because we've got the wire frame superimposed. With that shoulder selected now I can go to the rotate tool and then rotate and we can see that the other parts of the character are actually following it.

And this is how hierarchies work. The shoulder here is the parent of the elbow here. And the elbow is, again in turn, the parent of this wrist object here. The rule with hierarchies is that the transforms of the child are inherited from the parent. That is, the position or the end result of where this elbow is, is going to be inherited from the position rotation and scale of the shoulder.

Children inherit the transforms of their parents. Same thing with position. If I use the move tool and move the shoulder, we'll see that its children are going to follow. I'll undo that. Control Z. And again likewise with scale. Scale is inherited too. Undo that with control Z. Pretty simple. Pretty basic stuff. The other rule to keep in mind is that a child can only have one parent. A parent can have many children. And in this model for example, I have a pelvis and it's the center of the hierarchy.

And everything else is a child of that pelvis. All right? We've got the thigh joints here. You've got the hip left and hip right. Those are children of the pelvis. And we've got the chest here. That is additionally a child of the pelvis. That means if I select the pelvis and transform it, position, rotate, or scale it then those objects will all inherit that transform. We can see the hierarchical structure in the scene explorer. That's one way to do it. I'll open up that scene explorer.

Here it is. And what we've got is one object, the pelvis and a little right-facing arrow there. If we open that up it's going to show us all the child objects. And there's a nested hierarchy here. Children can have other children. In this example, all the links or the parent-child relationships are already created. Later in the chapter we'll look at how to make and break links between the objects. That's just a basic introduction to the concept of hierarchies in 3D.