NHR-1 – Skeleton Structure

As already indicated the Avastar rig contains 139 Bones. These Bones are organized into groups for different purposes. And each group can be displayed or hidden depending on the current task. This is achieved by sorting the groups into Bone Layers. we have already seen the Bone Layers display in the Object data Properties window (in the Skeleton panel). And we have also seen the Avastar Visibility Panel further down in the same window.

The Bone Color scheme

You may have noticed that the bones follow a color scheme. Here is what it means:

• Green: Controllers, used for animation.
• Blue: The Base Skeleton normally used for weighting.
• Red: Attachment points, used for animation.
• Orange: Collision Volumes, used for calculating physics behavior and used for fitted Mesh.
• Yellow: IK Bones, used for Inverse Kinematic animation.

The main control Bones

Here is a more detailed description of the Bone Groups:

The main control bones are only used for posing and animating the character. These bones are divided into:

• Arms
• Legs
• Torso (include COG)
• Origin

The COG (Center Of Gravity) is used to move the character relative to the Origin. The COG can be used within your animation when you want your character to move around in space.

The IK Bones

The IK Bones are only used for inverse kinematic based animations. The bones are divided into:

• Hands
• Hand Pole targets
• Feet + Foot Pivots
• Foot Pole targets

Since IK animation is a very powerful animation method we will take care of this in a separate chapter (where we will setup IK for our working model, the Horse).

 The Extra Bones

The extra control bones are very similar to the main control bones. They have been separated only because SL does not use them in the default Avatar (see note below). However you are free to use these bones as you like. The bones are devided into:

• Skull
• Eyes
• Feet
• Toes

Note: eyes are actually used for eye movement. However eye movement is mostly controlled by the viewer. So in most animations the eyes are not included. Hence we added them to the extra category.

The SL Base

The 26 SL Base bones are the core bones of the Avastar rig. However you touch these bones only for skinning (attaching the animated mesh to the armature). Hence these bones will contain the weight information of the mesh (see note below).

However, each SL Base bone has a corresponding Control bone of the same size and at the same location. There relationship is best described as master/slave with different roles:

• The SL Base is for skinning
• The Control bones are for animating
• The SL Bones strictly follow the animations of the control bones

We have separated the blue skinning bones and the green animating bones for various reasons. Here are some:

• The SL Base bones do not follow the Blender name convention, making it hard to use Blender’s built in Mirror functions.
• The avatar skeleton is strictly specified by Linden Lab. Thus we must export the bones with the exact names and the exact configuration as specified. The SL Base bones are created according to the specifications and thus are fully compatible with SL.
• While the SL Base is fixed, we are free to use the Control bones as we like. They have been setup to work properly with Blender’s standards (also for X Mirror). We even can add more control bones if that helps our animation.

But whatever we do on the control bones side, at the end Avastar will break everything down to animate the SL Base bones. These animations will eventually be exported to Second Life.

Attachment Bones

The SL Avatar has 32 attachment points where you can attach items to the character. The Avastar rig provides these attachment points as well in form of bones. These bones are currently provided only for animation purposes.

In principle you could reuse these bones for weighting as well. But this is not at all supported by Second Life.

E.g. the weighting is not always recognized and sometimes the SL Importer will reject the import of weighted attachment points. Hence we recommend highly to not weight these bones unless you like experimenting.

Animating the attachment bones is fully supported by Avastar and by Second Life.

Volume Bones (Fitted Mesh)

The 26 volume bones (19 in Avastar 1.0) have originally been used for representing a very light weight model of the SL Avatar. This model was (and still is) used for calculating the interaction of the avatar with the environment.

Avastar provides these bones as well for supporting the “Fitted Mesh” development. Actually the Volume Bones are officially accepted (by Linden Lab) as additional deform bones (bones which may have weight information).

This is still a work in progress. We will provide an extra course about Fitted mesh once the specifications are settled and Avastar is optimized for the task.

Structure Bones

The structure bones have been first introduced to visualize the connections between the torso and the limbs (green bones) but otherwise they do not play an important role.

Later we added support bones for the IK animation of the feet (yellow bones).

In general you can use these bones for your animation purposes. We will refer to these bones during the ongoing course as needed.

Eye Target

The eye target is used to control the eye movement in a natural way. this target actually controls the eye control bones (yes!) which in turn drive the SL Base eye bones (yes!!)

So the eye target operates as focus point. That is, the avatar will always look at the eye target.When you move the eye target away from the avatar, then from a certain distance on it will look straight. On the other side when you move the target very close to the eyes, you will get cross eyes (see image)

All of those objects that contain, or control other objects in the scene at any extent, have a little plus (+) sign beside their name. As we can see, the Avatar has one. Click on that to open the Dependencies Tree under this object. Clicking on the Avatar plus (+) sign actually shows all immediate children of the Avastar rig And as you can see the children again have a rich sub structure.

I have expanded the UpperBodyMesh to see this object’s children as well. And here you see for example that even Modifiers and Vertex groups are organized as children of mesh Objects. Those are not actual Objects yet they are still in there because they are dependent by the existence of that mesh in the scene.

What we need for our skeleton editing is contained in “Pose” part of the Avastar hierarchy.

Hint: If the Pose entry does not show a plus sign, then left click on the pose icon, or on the text “Pose”. This will set your armature into Pose mode, from where you now can navigate down the bone hierarchy.

More about the Outliner Icons

Let’s take a look at those little signs on the right hand side of the Outliner:

• The first from the left, the Eye icon, means that the object is visible in the scene. Clicking on that will toggle between showing and hiding that object in the 3D Viewport.
• The icon in the middle toggles the selectability of an object. Clicking on that icon enables/disables the ability to select the object to which it refers.
• The third icon, the little Camera, toggles that object’s visibility upon RENDERING. Hence, unless you’re going to make actual renders of your scene, this one might be useless to us.

Hint: If you just left click on an icon, then only the directly associated object is affected. But when you use CTRL + LMB then all children of an object are also affected. This is useful for example when you want to select an Object with all its children

Now, in the Outliner, click on the Pose “+” sign to open the actual hierarchy of our avatar. In the picture on the right, I opened the Hierarchy tree a bit further. Always make sure to open the tree that belongs to the green Avastar Control Rig, the one that drives the SL skeleton for animation purpose:

The Control Rig

The root of the Control rig is the COG Bone. In the Outliner you find it as a child of the Origin. In the 3D View the COG Bone is the one that sticks out from the Avatar back (and has the little wheel icon). If we continue expanding the tree, under Chest, we can see the CollarLink Left and Right and….guess what? By default the selection toggle icon is disabled on those for selectability (the little arrow icons)!

That’s right, this is what we were looking for: we have to enable the selectability of these bones. After you have done the collar part, proceed with the HipLink bones that connect the Pelvis to the leg bones (below PelvisInv in the hierarchy). Now all Link bones are selectable, so that we’re ready to edit our skeleton efficiently and safely.

So, after this small excursion into the Outliner i am sure that you will step back to the Constraints panel in the Tool Shelf and just enable structure selectability from there.

Best Practice Tips

Use the Default Skeleton

When we are about to edit skeletons for any game engine that allows that, it is always a good practice to start your work with the default skeleton. Even if the size and/or shape of the default skeleton are not matching our custom character. We can do this matching while we are editing the skeleton.

Avoid Object scaling

In any case you must without any exception avoid mixing Armature Object scale and skeleton editing together. This might end up in unexpected and unwanted results (resulting in bad surprises…).

The use of the default avatar ensures a better comprehension of the skeleton’s values, SL side speaking. The resize process will be carried by the new offsets parameters we’re about to edit bone by bone for our character.