Human fingers are pliant and soft; the finger surfaces conform to some extent to the local object surface as it is being grasped. In order to be able to recognize the human grasp, we should be able to extract some contact information between the hand and the object. Contact between the hand and the object is represented by single effective points of contact; each effective point of contact represent the contact between a particular finger segment (the palm counts as a "finger segment") and the object. These points of contact are shown below:
The filled triangle represents the palm while the thick circle and square represent the fingertips. The thinner circles and squares represent the more proximal finger segments. The contact web is the 3D graphical structure connecting the palm contact with the rest of the contacts illustrated below:
Associated with each contact point are the 3D location and the object normal at the effective point of contact (the latter to approximate the force exerted). This structure is used as the basis for the construction of the grasp taxonomy, from which the human grasp used in the task is recognized.