Attachments are just regular objects, either Prims, Sculpties or Meshes which have been “attached” to an avatar. Furthermore, meshes can be either static (similar to Prims and Sculpties) or rigged (can be animated similar to the default SL Avatar)

Rigged Mesh attachments

Rigged Mesh attachments are like any other attachments, but they additionally contain extra data which makes them fully controlled (animated) by the Avatar skeleton.

Fitted Mesh attachments

Fitted Mesh Attachments are a special form of rigged mesh attachments which additionally use a specific subset of the Avatar’s skeleton (the Collision Volume Bones)

Attachment points are hooks where you can tie objects to your avatar. In Second Life we have 32 attachment points where other objects can be attached. These attachment points are distributed all over the avatar (marked as red spots in the image). And each attachment point is “glued” to one of the 26 bones of the SL skeleton. Technically attachment points are regular Bones (for more about Bones see further down).

History

Before Mesh objects have become available, we had only static attachments: either rigid Prim objects or flexi Prim objects. These attachments only move along strictly in parallel to the movement of their attachment point. Thus something attached to a hand attachment point will move with the hand, something attached to a head attachment point will move with the head, etc.

Static Mesh Attachments

Meshes are by default rigid Objects which behave exactly in the same way as regular Prims and Sculpted Prims. A Mesh object can be attached to a single attachment point exactly like Prims or Sculpties. So by default they move along with the Avatar like Prims do.

However, besides static Mesh Objects we can also create Rigged Meshes…

Rigged mesh and Skeleton

Meshes can be animated in exactly the same way as the SL Avatar itself is animated, by using a Skeletal Animation technique. In the context of SL this technique is named Rigged Mesh. So Rigged Meshes follow the movement of the Avatar in a more natural way. Like a dress can bend when the Avatar sits down, or a jacket follows exactly the arm movements.

In very general terms a Rig is the animation system that is used later for animating the meshes. Rigging is the construction of such an animation system. In the context of SL the Rig is equivalent to what we know as the Avatar Skeleton.

The SL Default Rig

When we create attachments for the SL Avatar, then we actually have to use the SL Rig without changes. When we later upload a mesh to SL then -by default- the SL Importer assumes that the correct Rig was used, thus it does not even upload any skeleton information, even if it was modified in Blender (see below)!

The Second Life Basic Skeleton defines 84 bones for very different usages. Though you might only know about the 26 SL Defrom bones (mBones).

Avastar’s Basic Skeleton provides the complete set of bones that are also defined by SL. Plus a couple of extra bones mainly for animation purposes.

(1): The cBones are used for collision detection and for Fitted Mesh Attachments

Bones in the Basic SL Avatar:

• 26 Deform Bones (mBones).
• 26 Collision Volumes (fitted mesh).
• 32 Attachment points (hooks).

Bones in the Basic Avastar:

• 26 Deform Bones (mBones).
• 26 Collision Volumes (cBones) (1).
• 32 Attachment Bones (hooks).
• 29 Animation Bones.
• 14 IK Bones.
• 9 Extra- and Structure Bones.

The SL Avatar has been extended with a large set of extra bones for face, hands, wings, tail and hind limbs. You find a detailed description in the SL Skeleton page

 Read more about The SL Skeleton

• Copy weights.
• Clean weights.
• Find unweighted.
• …