Well, let's get started:
Parent + Child
This is a well known way of working within hierarchies. Hierarchies are an easier way of categorizing within a rig or the entire model. So, for example let's say the person who created the model rigged it and then named all the joints - the person animating can then see what joint is what and how they are connected.
Bones and Joints
Joints (or to name them correctly Joint Deformers) are places where the model can be bent or deformed. Clicking again while the joint tool is still selected and another joint is then created and that joint will then be the child of the previous joint.
Skeletons
You can create create another child joint from another joint (the wrist is the parent joint to the knuckles in the hand). This is for more complex hierarchies that are usually used for more detailed, complicated models. One of the things the chapter says (and something I learnt from my past experiences in this) NAME THE JOINTS! (properly I might add) - it will confuse you later on if you are not aware of what joint is which and what it moves. It's also worth knowing that you can mirror joints - which is a time saver if the joints are the same on the other half of the model.
Creating the Rig
Good knowledge of the sort of anatomy for the model you are going to be rigging is always good to know, if you're going to rig a human it's easier to use yourself or a friend as a reference to know where exactly the joints are going to be. When the rig is finished you;ll want to create a bind pose. A bind pose is basically a starting pose that you can easily go back too in case something happens. It's also said that it's good to usually have a starting pose in mind: T Pose or Y Pose.
- T Pose: standing with their arms outstretched looking like a T. This stops the overlapping of parts.
- Y Pose: where the arms are stretched at a 45 degree angle. This puts the shoulders in a more natural position while maintaining distance between arms and legs needed for skinning.
You will want to take into account alignment consideration when it comes to joints rotation axis. To simply put it - have the rotation points make sure the X Axis of the joint is in the direction of the length of the bones, have the Y and Z Axis pointing in the same direction, ideally with the Z rotation pointing to the back of the Y and the Y rotation pointing down.
When joints aren't properly oriented will lead to a Gimbal Lock. Gimbal Lock happens when two axis overlap. When joints are placed - SET THE VALUES OF ROTATIONS TO 0! And referring to an earlier point - when when building the skeleton use mirror and duplicate tools to help make it even.
Joint Limiting
Self explanatory, obviously your joints will only bend so far - unless you're double jointed (or flexible). So, when it comes to determining the limits of your joints in your model for a human character for example - use your body to determine where those limits are.
Kinematics
Kinematics are the study of how things move when forces act upon them. There are two approaches to this:
- Forward Kinematics (FK) - the case joints will move the child joints to the position you are looking for. Like how the right shoulder joint will move the other joints that follow down the rest of the right arm.
- Inverse Kinematics (IK) - makes the joint that would be the child become the parent joint to the joints that come before it.
To have your animation have good, natural movement - you will need to use both forms of kinematics.
Skinning
It's connecting the skeleton to the model - or binding as it is also known as.
Rigid Biding
Good for skinning things that only have one surface. One vertex is assigned to one joint and every vertex is influenced by that joint.
The problem you'll get with rigid binding is that you get strangely stretched and punched parts of the surface where the bend is. To avoid this you'd use a specialized lattice like a flexor (that rounds out the surface at a binding location) can improve appearances while flexing. The lattice is then bound to the surface so when you move the joint it is bound too - the model moves more well. Remember, rigid binding is different to rigid bodies:
- Rigid Binding: a type of influence of the joint deformer on the surface.
- Rigid Body: a surface that can't be deformed.
Smooth Binding
This is better for organic models as it offers you the chance to add weight to the influenced joint - this is so that the joint can influence some of the vertices more than others.
Muscles
This makes for better realism when simulating muscles under the skin. Muscle deformers take on the role of making animation look as if the muscles are doing the movement in the joint. When they're attached to the right places on the model, and change shape when it's translated onto the model.
Rigs can also be useful for things that don't need a skeleton - say you're animating a horse, you could easily use a rig on the tail to get the motion you are looking for.
Well, that pretty much the information I got from this chapter of the book - to be honest some of the things like kinematics I knew about previously but it's always good to refresh your memory on certain things every now and then so it can stick - all in all it was an interesting chapter. It's given me a lot to think about when it comes to my own - hopefully you will see all this in my own work.
Next blog post: will be the next chapter of this book - talking about animation principles and the like. Until then :)
Bibliography
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