The limb-orientation geometries - used to model poses and action

Action can be seen as a sequence of coordinated changes in limp positions. Each limb has its own geometry of possible movements. I simplify the geometry of limb positions in the following way:

• I use polar coordinates with its origin at the centre of the joint closest to the centre of gravity.
• e.g. the hip-joint for the upper-leg, not the knee
• I use three orthogonal dimensions: forward, sideways, and twist
• I treat limbs as straight and rigid.
• I treat the hips, the chest, and the head as rigid, with the waist and the neck as joints.
• I treach hands and feet as single rigid limbs.
• I treat the line of vision as a straight limb, rotating about the eyes as a single joint.
• I use common terminology to describe the angles, forward, sideways, and twist.

• We simulate a stick-figure with scalable vector graphics image (SVG): a tabular representation for the limb-size information required for a simple representation.
• Ignoring changes in time, we simulate a pose with limb-angles relative to gravity: a tabular representation for the information required for a pose, by specifying the orientation angles for the limbs.
• The angles of rotation are frequently updated (using SVG and SMIL animation on the browser).
• Adding time to the SVG image, we simulate action with animation: a tabular representation for the information required for an action sequence, using the SMIL standard for animating an SVG image (SVG+SMIL).

Geometry is different for vision and action. For vision it makes sense to think of a 3D Cartesian space, with a viewpoint that depends on the line of sight. Action at the joints is in polar coordinates, with each joint in its own coordinate space which depends on the limb more directly connected to the waist or centre of gravity. Gravity depends neither on the line of sight nor on the current pose.

• Gravity can 'normalize' the 3D space of vision by defining the vertical axis.

Skills as stored instructions for an information-processing system: in general I don't care whether skills are hard-wired into the brain and neural system, whether they are software, or whether they are a combination of the two. However, since my background and experience is primarily with software, I shall use that as primary analogy. I shall focus on the system design, looking at architecture and feasibility. The hardware / software question then becomes an implementation issue.

Perception of gravity is 'always on', and does not appear to require any action. It provides a vector from approximately the eyes to the centre of the earth. (For modeling convenience, we shall also assume such a vector from the waist (centre of gravity) to the centre of the earth.