Skeleton layout part 2

Since my intital post on skeleton layout I've figured out how to use Google Documents... so here is a basic biped skeleton:
Biped skeleton

Things of note:

• There are two stored poses on the skeleton for use with the Pose Manager tool - the model pose and T pose.
• It has two roll joints in the upper arm, two in the forearm and two in the upper leg. You can get away with a single roll joint in each area if you have to, but two is what I'd consider the minimum for nice twist deformation. If you want to implement stretchy limbs for a game engine (so no joint scaling, just rotate/translate) you need more. Anyway, I'll come to all of that over the coming posts.
• The root joint at world orgin is a requirement of the runtime animation system, so unless you're producing game assets you won't need it.
• COG (center of gravity) position overlaps with spine_01. The reasons for this will become clear when I post on spine control set up.
• The top of the legs have the same tY and tZ position as the COG joint, creating a T-bar configuration in the hips area. I'm a big fan of this kind of layout as it means you can rotate the COG of the character without legs raising off the floor. It's also the preferred layout if your skeleton is to be used for motion capture.
• Fingers are not fully articulated

Skeleton layout

Generally I have some kind of joint budget I have to work within when starting out with a new character. For a standard NPC (none playable character) where we are aiming for ten or so on screen at once the aim is to come in under 50. There's generally a bit of wiggle room there; some come in comfortably under that and others are a touch over. Joint count isn't the only factor in how efficient a character is; the number of animated channels per joint has an impact on animation data footprint, number of skinWeight influences per vertex on skinning processing... I'll come onto these things in later posts but for now the point I'm making is that this is the point where you need to identify how to best use your joint budget; do I really need a fully articulated hand or will it be more noticeable in game if I use a more basic joint layout there and use the joints saved for extra roll joints in the arms and legs? It can be helpful at this stage to print out a front/side view of the model and draw your skeletal hierarchy over the top.

Initial layout is done in a relaxed model pose as it's not practical for character artists to model in the T pose (also known as the Jesus pose) that you use as the starting point for a control rig. This tends to be with arms at around 45 degrees, elbows slightly bent, legs and feet pointing out slightly. Being able to manage and switch between model and T poses will really help your work flow and will be the subject of my next post where I'll cover the pose manager tool I use for this.

The same skeleton in model pose (initial layout) and T pose (ready for rig construction)