I think of poses in terms of an actor on a stage. At the most basic level, there are two objects: a stage and an actor on the stage. Since we want to look at the poses and the action, we need an audience or a camera with a perspective, i.e. a viewpoint relative to the actor and the stage.
The stage is represented by a grid. Typical play productions use the actor's perspective, when facing the audience, to assign right and left. To make it less confusing, we shall use the audience perspective in assigning right and left. Considering the width of the stage, centre stage is 0. The width (also called 'x'), increases to the right, so that left of centre is described by negative numbers. The depth (also called 'y'), is 0 at front and increases to the back of the stage, i.e. away from the audience. The height of the stage is 0 at the stage floor and increases with height.
The actor is represented by rectangular boxes, cylinders, and balls. The balls represent joints that can rotate and twist. The actor is described by the size of boxes, cylinders, and balls that represent the major skeletal components that are involved in a pose.
Poses are described in terms of angles between limbs of the body. The angles are obtained by rotating relative to the joint connecting the limbs. The waist is seen as a joint and as the centre of the actor. Distances increase as they are further from the waist by direct connection. For example, the wrist is closer to the waist than the fingertips, however the hand is pointed.
Distances for the stage and for the actor are expressed in mm. Angles are expressed in degrees.
To model poses, we encourage the explicit control of stage dimensions, limb sizes and joint rotations.