Legend:

• Top most dot = the crown
• 2nd dot = sternum point (center of mass - upper control point)
• 3rd dot = dan tien (center of mass)
• 4th dot = perineum
• Top red circle = upper mass
• Bottom red circle = lower mass
• Top (horizontal) blue line = nipple line
• Middle (horizontal) blue line = elbow line
• Bottom (horizontal) blue line = "dan tien" line (corresponds to the nipple line)
• Left and right vertical lines = shoulder line / square of the body (Side Thrusting Routes)
• Middle vertical line = center line (Central Thrusting Route)
• The arcs = absorb and project from the the feet to the point
• The half circles = convex
• The full circles centered on the shoulder lines = concave

Thanks to Johnny Kuo for this excellent diagram.

More at the I Liq Chuan International Forum topic.