What is rigging in 3D animation?

A skeleton is a hierarchy of bones connected at joints. Each bone is a transform that moves its children, so rotating the upper arm carries the forearm and hand with it. The top of the hierarchy — for a character, usually the hips — is the root, and moving it moves everything.

A bone does not render. It is a handle with a position and an orientation, and its job is to tell the mesh how to move. Bones are placed inside the body at the points where it bends, and getting the joints in the right places — elbows at the elbow, knees at the knee — decides how natural the deformation can ever look.

Skinning binds the mesh to the skeleton. Every vertex gets a weight for each bone that influences it, and the weights usually sum to one: a vertex on the forearm might follow the forearm bone fully, while one at the elbow is split between the upper and lower arm so the joint bends smoothly. Real-time engines commonly allow up to four bone influences per vertex.

Most bad deformation is bad weighting: an elbow that collapses, a shoulder that pinches, a hat that drifts away from the head. The standard method, linear blend skinning, also loses volume when a joint twists — the candy-wrapper effect — which is why rigs add twist bones or use dual-quaternion skinning. Weights are set by painting, by automatic methods such as Blender's bone heat or Maya's geodesic voxel binding, or by a mix of the two.

With forward kinematics (FK), you pose a chain by rotating each bone in turn from the root outwards: shoulder, then elbow, then wrist. It gives natural arcs and full control, and it is how swinging arms and flowing tails are usually animated.

With inverse kinematics (IK), you place the end of the chain — a hand or a foot — and a solver works out the rotations of the bones above it. IK is what keeps a planted foot on the floor while the hips move. A pole target sets which way the elbow or knee points. Rigs usually give animators controls for both and let them blend between FK and IK.

An auto-rigger fits a skeleton to a character and solves the skin weights without manual placement. Most want the character in a T-pose — arms straight out to the sides, legs slightly apart — because it makes the anatomy measurable: the arms run along one axis, the limbs are separated from the body, and the elbows and knees are not hidden inside a bend. Some tools accept an A-pose, with the arms angled down, instead.

Mixamo made this familiar: upload a humanoid, mark a few points, and get back a rigged character. Auto-rigging works best on humanoids with clearly separated limbs, and a character in a pose, holding a prop or wearing a long coat usually needs manual fixes to the joints or weights.

Retargeting transfers animation from one skeleton to another — a motion-capture walk onto your character, or one character's clip onto another with different proportions or bone names. The retargeter maps bones by role (this is the left forearm, this is the spine) and adapts the motion to the new lengths so feet still reach the floor.

Studio's Rigging panel, in the Animation section, covers the whole chain. Auto-rig from T-pose measures the character — joint heights, arm span, shoulder width, crotch, ankles and leg spacing are read off the mesh — fits a 21-joint humanoid skeleton and solves the weights, running on your own machine with nothing uploaded. A mesh that does not read as a T-posed person is refused rather than rigged badly. For anything else there are humanoid, quadruped and chain templates to place by hand before binding.

Bind mesh to skeleton solves weights through the character's volume, so a body, armor and hair bound together as one group move together. Add control rig puts IK on both arms and legs plus a head look-at, and Bake IK writes the solved pose back to keyframes. The Motion library previews over 2,500 motion-capture clips from the CMU database on your character before you commit one; adding it writes ordinary keyframes you can retime. Characters that arrive already rigged, as GLB or FBX, keep their skeleton as ordinary, keyable bones.