IAC

Modeling for Animation Guidelines - by Tal Flint

Some of the things written here may be obvious and some my not. Just keep in mind that usually we tend not to pay attention to the most obvious things. Before you start modeling take a look at the reference pictures and the character sheet. Spend some time looking at the story boards and the animatic. This will help you to get to know the character. What it looks like from all angles, what's his roll in the movie, his range of motion and emotions. The way it moves, talks and feels will give you some guidelines as to how it should be modeled. A character that moves a lot needs more detail in the parts that deform – joints, neck , etc` . A character with a lot of facial expressions needs more detail then one that just stares into the distance.

Always remember – a modeling reference drawing is just what it sounds like – it's a reference not a template. Many reference drawings are not accurate or done by artists who have no understanding of 3D animation. If something doesn’t look right it probably isn't. It's better to go and ask about it before modeling than to have to fix or remodel it later.

To create a good model you need some basic anatomy knowledge. It doesn’t matter if it's a realistic character or a cartoon one – it still has to be able to move realistically in the 3D world. The modeler has to have some understanding of the muscles and skeletal structure and how the work. Looking at the character you are modeling in various poses will help you understand how it moves and deforms. One of the most important rules in modeling is keeping your edge loops right. In other words it's a way of keeping a smooth flow of the geometry. Keeping the smooth flow of geometry along the natural lines of the model will result in a better looking model and will make it easier to animate.

The next two samples show the same model before and after smoothing. Even in the non-smoothed model you can see that the basic structure and the flow of the geometry are kept.

Mimicking the anatomy helps in various ways – The muscle structure is cleaner and smoother, you have better flow of geometry, during the animation you'll get better deformations in the body.

The structure of the leg is kept during the bend, the muscles stretch and deform to the new position in a natural way and the joint keeps its normal structure. The model should look good but efficient. There should be enough geometry so it looks and deforms well, but not too much so it can still be animatable. Places that don't deform much during the animation should have less polygons then places that deform (joint, face, etc`).

Modeling body parts

Unless you are modeling all the muscles in the chest and abdomen, try to keep it as simple as possible. There is no need for too much geometry in that area. Depending on the character, 3-5 polygon loops are enough. The loops should follow the curvy contour of the body. Keeping this contour will help the body to bend correctly when animated.

Chest and shoulders

As in the torso the mesh should follow the contour of the body and the muscles. The edges flow from the chest area over the shoulders and down the back There are 3 places in the mesh where we get 5 polys that share a single point. This is done so we can change the direction of the flow of the polygons. The polys in the shoulder are built like a fan with the base in the armpit and spreading left and right across the shoulder.

Arms, elbows and wrists

The elbow should be modeled in a "V" shape, with the narrow part in the soft tissue area (the inside of the elbow). From there the edges keep the "V" shape, and slowly getting parallel as the get closer to the middle of the bicep and forearm. Because the wrist can bend in all directions the edges are kept almost parallel to each other.

Legs and butt

When modeling the upper leg, hips and butt keep the mesh simple as [possible and flowing along the curves of the body. The edges should form a wave shape starting in the front of the body, going up on the sides and down again in the back.

The next few pictures show the body in motion. Watching how the muscles deform will help you understand how the mesh should be build so it can smoothly deform into these positions.

The head

Modeling a head for animation requires more then just getting it to look like the reference images. You can get to the exact shape of the head with a bad topology structure. The final model should look like your reference, but it should also be able to get to all the different facial expressions. There are two major issues that should be considered when modeling the head:
1) Geometry - refers to the overall structure of the mesh – how many polygons are used, where they are placed etc'.
2) Topology – refers to HOW the polygons are laid.

The model should have enough data in it to allow it to animate well, but also be efficient enough so you don’t have too many polygons. The structure of the mesh should reflect the bone structure of the skull, the muscles that deform the face, the fat areas and the personality lines.

The skull determines the basic shape of the head and the muscles determine how the softer areas will look and deform. The fat areas and the wrinkles show the "character" and personality of the model. One way of achieving this is by modeling in "layers". Try to think of it as deconstructing the head into its elements and then rebuilding it according to the order in which they are layered.

First start modeling the bone structure of the head. That will give it its basic shape. After that is done start adding all the muscle loops to control the movement of the mesh.
Add the fat tissue (in the cheeks, under the eyes etc'.)
Add all the character details – skin folds, wrinkles……..

By deconstructing the head and modeling in layers you get more control over the final shape of the head and all the edge loops. Looking at the muscle structure of the face you can see that there are 2 main groups that are connected by other muscles: The mouth and the eyes. These are circular muscles that are connected by the linear muscles of the cheeks and the jaw.

Modeling edge loops is extremely important when modeling heads. The face area is crowded with muscles that move and deform to create all the facial expressions. Improper structure of the model will cause some expressions to look bad and some may not be doable. Modeling the edge loops according the shape and flow of the muscles will make the mesh look better and deform well when animated.

No muscle works alone. Every muscle that contracts pulls another group of muscles that deforms part of the face. To get good deformations the deferent parts of the face need to connect smoothly to each other.

The colored parts show the main muscle groups of the face. Eyes and eyebrows, cheeks, jaw and lips. A movement of one of these muscle groups will make another group deform as well. You can model a head that will look good in a static position, but will move unnaturally when you try to animate it.

This model looks good, but you can see the muscle structure is incorrect. There edge loops are wrong and the different parts of the face don't connect smoothly. In the next picture the edge loops are correct and the connections between the different parts of the face are natural and smooth.

Both models look almost the same, but the correct topology of the second model creates a better structure and enables a better and more natural facial animation.