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Now that we understand the Joint tool and how to use it, let's take a look at tools that allow us to manipulate joints more easily. Now this chapter is basically just going to go through some of the tools, and then we'll use them later to rig the character. So the first tool I want to look at is probably one of the most important tools you need to know in character animation, and that's the IK Handle tool. In this one we're just going to take a look at inverse kinematics and how it works, and basically how to set it up.
So inverse kinematics is one of two ways to manipulate joints in a skeleton. The first way is called forward kinematics, and that is basically rotation. So you rotate the joints into place, and that's probably the more natural way to manipulate joints, because the bones in your body basically just rotate around each other. Every motion in your body is in some way a rotation of joints.
Inverse kinematics introduces the concept of a goal, in other words, a place where all the joints need to rotate to, so this allows you to position the end of a joint. So the easiest way to remember it is, forward kinematics is when you rotate joints, inverse kinematics is based on position. So you tell the joints where you want to be in space, and then they rotate to that point. Let me give you a quick demonstration. I've got two sets of joints, they are identical joint chains.
One is unencumbered, it has no inverse kinematics on it, so this is manipulated using forward kinematics. The one on the right has this little IK handle on it, and that allows us to manipulate the joint using inverse kinematics. So I'm going to go out to a side view here, and I'm going to zoom in a little, so that we can see what we're doing, and forward kinematics again, is rotation. So if I wanted to take the end of this joint chain and place it on the origin, I would have to rotate all the joints into place, so let's do that very quickly, I'm going to hit E, to get into Rotate mode.
As you can see, when we start rotating, it's kind of hard to actually hit that target, so I have to rotate this one away, and maybe this will towards it, and this one towards it again, and then maybe we rotate this one in. I'm basically estimating, I'm not really being very accurate in the way that I place these joints, because rotation and position, they don't match up really well. But inverse kinematics, it makes it much more easily.
If we want to be exactly on the origin with this inverse kinematics chain, all I have to do is select this little cross at the bottom, and that's called ikHandle1, then just hit W to go into Move mode, and just translate this to the origin, and it was just simple as that. Maya automatically rotates the joints evenly to make them hit that target. Now if I go beyond the target, obviously we're going to have a problem with that not going as far as we want, but generally within the range of the lengths of the joints, everything will sync up.
So as you can see, each one has a different purpose. Typically, forward kinematics is a little bit more natural, because it's based on rotation, so will naturally give you those arcs you want to see in character animation, but they both have their place. So now that we understand how this works, let's show you how to set it up very quickly. So I'm just going to do a File > New Scenes, so that way we'll just clear out what we have, and again I'm just going to go into my side viewport, and select Skeleton > Joint Tool, and let's just do a very simple joint chain and I'm just going to do a two-bone chain, so I'm going to go ahead left click here, left click a little bit ahead of this middle line here, and then click again to give it that nice bend. And the reason we're giving it a bend is to tell it which way we want inverse kinematics to bend the joint.
Now we did this a little bit before in the previous chapter, and let's show you why we do this. So now that we have a joint chain, we can set up inverse kinematics. So all we have to do is do Skeleton > IK Handle Tool, or if you're on your shelf you can select it using this icon, either way it'll work, and then what we want to do is select the first joint we want in the IK chain, in this case, it's the top joint, and then the last joint, and in this case it's the bottom joint.
We don't have to -- we can actually have IK chains in the middle of a string of joints, but in this case we want it to the end. And what it does is it creates this IK Handle, and once we have that we can select it, hit W, go into Move mode, and as you can see the joint is bending in that direction. Now if I were to draw the joints straight, it wouldn't understand what direction the joint is in, and it won't be able to bend it, that's why we give it a little bit of a bend.
Now if we take a look at this in the Outliner, you'll see we have our joints here, but the IK Handle is actually a separate object that's outside of that joint chain, and this is what allows it to move it separately, so that it can position the end of that joint. So those are some of the basics of IK Handles and inverse kinematics in Maya, so just remember we have two ways to manipulate joints: forward and inverse kinematics, and each has their place.
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