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Skill Level Intermediate
- [Steve] Hi, this is Steve Wright welcoming you to this week's Nuke Nuggest, Faster Rotos with Hierarchical Animation Techniques. Your roto work can be faster, and the motions smoother, by building a hierarchical skeleton structure that matches the body segments and joins of your target. Here's what I mean. I've got this little walk cycle here, and I've done it all with hierarchical animation. So I've built a set of folders and linked them together in such a way that if I grab the thigh, for example, I move the entire leg, go and do that, then I can go to the knee, right here, and pivot there, and do that and the foot.
And in all cases, the pivot point is carefully positioned at the appropriate joint position of the target object. Now let me show you why transformation animation is superior to point twiddling. Let's go over here to this guy and open this guy up. What I have here is a simple rectangle. Using a transform, I've animated it to rotate 90-degrees. You'll notice that it maintains its shape just fine. However, let me hide that, turn on this one, and now, as I step through it, you can see the shape deforms, it's actually shrinking, and then it gets larger again at the end.
So what's going on here? Well I can show you with these guys. With the point interpolation, the point moves in a straight line between key frames, so here we go, watch this. See, every one of those points is moving in a straight line, and that explains why it gets deformed here in the middle. So, if you use point interpolation, the path of motion is a straight line. If you use transformations, the path of motion is an arc.
And for biological things, arcs are much more natural. Okay, we're done with that. Okay, let's go back to our original setup here, and I'll go to my mainframe here. What I'll do is I'm going to add a couple of more key frames in order to finish off the shot. So as I'm going forward, you see I do not have any animation on my thing, so, let's jump to the last frame. I'll pick the right thigh, I'll drag it over here, I'll rotate it there, and I'll finish up with 94 and minus-seven.
and for the rotate I want minus-15 degrees. Okay, that positions the thigh. Next we'll go to the knee. Set this guy for a rotation of one, then we'll go to the foot and set that guy for a rotation of six. We'll pull this down a little bit, so you can see a little bit more of what's going on. Okay, so that's frame 16. I'll come back to frame 13, put an in-between key frame here.
Okay, so we'll move this guy like so, and we'll set him for 45 minus nine, and the rotation I want on this frame is minus-seven. Then we'll go to the lower leg here, set that for minus-one. And then we'll go to the foot, and set that for about six. There. Okay, and we're done. So there's my last key frame on 16, 13, and then back to here where I left off.
So now let's just step through this, and you see we have very nice animation that stays on target because the motion is organic. So how do we make these folders, how do we build these hierarchical structures? I can show you that right over here with this guy. I'm going to jump the play head to my key frame. Okay, so here's how we build the hierarchical structure. I'll select the root folder, and click the plus sign, and we'll name this leg.
And starting at the top, we select the folder and the transform tab so we can see the pivot point. Remember, to move a pivot point, you have to hold down the command or control key. And now we need to move the pivot point to where it belongs on the hip. So I'm imagining that's where the hip is for the leg. Then we'll take all of these guys and put them inside the leg folder. Now, when I rotate my leg folder, it takes all of the shapes with it.
Alright, now let's add another folder under leg with a little plus, we'll name that knee. And we'll take the lower leg and the shoe and put them inside the knee folder, there we go. And now if I select the knee folder, there's my pivot point, command or control, move the pivot point to where it belongs on the physiology. Now, if I rotate the knee, it'll take the leg and the foot with it.
Next, under knee, we'll add one more folder and call it foot. Okay, and then we'll take the shoe and put it inside the foot folder like so. Okay, I now have a proper hierarchical structure. So now if I grab the leg, it all goes there. I grab the knee, there we go. And then I grab the foot, oops, I didn't do the foot pivot point.
Look at that, wrong wrong. So let's use command or control to move that pivot point, and we'll move it down to where the ankle belongs right there. Alright, now the foot rotates correctly. Got to remember our physiology, right? Now we can do a little cosmetic alignment here if you like, because these guys don't look like they're inside their folders, they really are. So we can take the thigh, for example, pick it up and move it right underneath the leg, you got to get right there.
And now it shows up right under the leg folder, which is kind of cosmetically nice. Again, this is just a cosmetic thing we're doing here. And then I'll grab the lower leg, and put that just under knee like so, there. And of course the shoe is under the foot folder. Alright, so there, that looks pretty. So now, we can select the leg, do our thing, select the knee, do another thing, and select the foot, and do the last thing.
So there you have it. Using hierarchically-linked folders to speed up your roto work and produce smoother animation. Be sure to check in next week so you don't miss out on my next new nugget.