Unity says there is Rigging and Skinning, but i see only Rigging inside Modelling tools?

Questions & Answers
1

Unity guide says:
Rigging - is a skeleton creation.
Skinning - mapping skin to skeleton bones.

But inside every modelling tool:
Rigging = skeleton creation + mapping skin to skeleton bones SIMULTANOUSLY.

What is going on?

  1. Does this mean that I CANT have Rigged model WITHOUT Skinning ??? (YES)
  2. Can model be animated without Rigging? Is rigging required for animations? I dont understand. (Answer: Rigging is not required for “Mecanim Generic” animations)
  3. Why Unity uses separate terms: Rigging + Skinning, while all other world using only Rigging, where Skinning is just a part of Rigging process? This makes me misunderstanding animation process. (Answer: Rigging and Skinning must never be mentioned separately for Animation process, look (1), whole world calling it just shortly “Rigging”)
2

Rigging without skinning is totally useless. Only the skinning information gives a relation between the bones (the rig) and the actual mesh (the skin). If a rig isn’t skinned it just consists of invisible bones which can be animated but have no influence on the Mesh around.

So if you want to use skeletal animations your model need to be rigged and skinned.

3

3d animation is complex - there is always confusion.

A 3d model is a collection of vertices. Typically called a mesh. One approach to animate it is called skeletal animation.

You create a 3d “skeleton” that consists of joints and bones. (The joints really just represent transformation and rotation matrices used to deform the vertices at render time) This skeleton is the rig. It can also contain ik controls to help pose it. The skeleton is posed in various keyframes to create animations. walking, running, jumping…

This is more efficient than keyframing the entire list of verts (like old quake md2) because the gpu can be used to perform the bone transformation and rotations. The verts are already stored on the gpu in a vbo - this is the t-pose. The gpu shader is the “skinned mesh renderer component”.

In order for the skeleton to be used to deform the mesh, each bone must be associated with the vertices it affects in the mesh. This process is sometimes called “skinning a mesh”.

In Mecanim, you can take an animation built for a different mesh/skeleton and retarget it to any mesh. This relies on the fact that both skeleton rigs are humanoid and similar. This is very useful and innovative.

Hope that helps clarify things for you.

The reason the vocabulary is so varied is because different tools have evolved that call it different things and use different approaches.