Presentation About Anatomy- Based Joint Models for Virtual Humans Skeletons Prepared By Khloud Zain Al-Abdeen Najwa Al-Ghamdi

Introduction Addressed Problem Solution of this paper Pseudo-code Achievements of the Proposed Solution Comparison between this model & other models The weakness of this Model

Introduction The use of computer graphics in many applications was dramatically growing in the last decade, especially in area of medicine and virtual reality. Such applications are developed using human body models. The requirements of these models determine the degree of complexity and fidelity of these models to the human anatomy and the realism of movement.

Addressed Problem The Previous models lack in the ability to perform correct motion and need a complex control system to look like humans. And this is due to the simplification that the developers had been approached in building their models

Literature review 1.Hierarchy 3D (H3D) Model By Boulic et al. Specification 1.Each joint has only one rotational or translation DOF. I.e. building a joint of two DOFs, like a wrist, require creating of joints. 2.Each joint is associated with a matrix, which represents the relationship between this joint and its parent and the root joint of the model.

Literature review 2. Axis Position Joint (APJ) Model proposed by Zeltzer, and extended by Silva. Specification 1.Each joint in this model has its own local reference frame (coordinate system) to define position and orientation of it, in means of its parent coordinate system in the body. 2.Each joint has several DOFs. 3.A pointer to children is associated with each joint. 4."The position and orientation of any joint of the tree can be obtained by composing the homogeneous transformation matrices that define the reference frames of each joint."

Literature review 3. Animal Articulated Skeleton Specification  support muscles and simulated skin in a tree architecture  consist of segments that are linked through three rotational DOF joints, that has their own reference model  Note that the segment is a composition of  bones  muscles  And skin.

Literature review 4. Spine and Torso Model Developed by Monheit and Badler. Specification  Virtual human torso is built using medical measurement data that are driven from the motion of every individual elements of the body such as vertebrae, muscles and ligaments, and the properties of bones and cartilaginous discs, with an easy way to control motion, suitable for ergonomics applications.

Literature review 5. Human Shoulder Model By Maurel and Thalmann Specification  based on the specula movement relative to the thorax  the hierarchical representation is not adapted  scapula is linked to the thorax by a 5 DOFs joint.  The other shoulder joints are 3 DOFs joints. Specula thorax

Literature review – criticism 1.Not realistic The previous models proposed that rotational DOF of a joint is able to rotate 360 degrees, which means that there are no constraint among the motion range 2.Lack of anatomic correctness the displacement that occurred to the rotation axis from its original position while rotation in some joints, was ignored.

Literature review – criticism Lack of anatomic correctness

Literature review – criticism 3. Distortion in the movement Most of motion measurements were calculated for each joint and each DOF individually, with isolation of the other related joints' Impacts to the motion of that joint. 4. Models are monolithically structured ▫object-oriented (OO) modeling and UML are recommended to overcome the negative consequences on using the monolithic architecture

Approach of this paper Human body will be represented as a tree, each node in the tree is a joint and the edges correspond to the body segment Every joint has a 4x4 LIM (Local Instance Matrix), which include the relationship between the parent and the child joint Graphic objects represent the bones associated to each joint in the tree Each object has its own a LIM (Local Instance Matrix) which defines its position in relation to the joint

Approach of this paper We can calculate the position and orientation of the graphic object, by multiplying LIMs of all joints from the root to the current joint and the object's LIM. The result will give GIM (Global Instance Matrix) of that object The possible movement of the joint is given by its degree of freedom DOF

Approach of this paper Types of Joints ▫There are four basic types that are needed to describe any human joint: 1.a Uniaxial joint which is described by a joint with only one rotational DOF 2.a Biaxial Joint type, with two rotation DOFs 3.a Poliaxial Joint type, which presents three rotation DOFs 4.a Plane Joint, which includes translation DOFs

Proposed solution : data structure used // attribute Class Joint { joint *child, *parent; int LIM [4][4]; Graphic objects * object; Degree-Of-Freedome[] DOFs; int no_dofs; bool is_root; }

Proposed solution : data structure used // method Class Joint {Void Move () { For (int i =0 ; i< no_dofs; i++) LIM *= DOFs[i].LIM Compute_GIM (); Object ->GIM = GIM * Object->LIM} } ////////////////////////////////////////////////////////////////////////////////////// Int** Compute_GIM (joint * p) { if (p->is_root) return (P->LIM) else p->GIM = compute_GIM( P->parent)* p->LIM }

Proposed solution : data structure used Class Graphics Object { Mesh m; int LIM [4][4]; int GIM [4][4]; } Class DegreeOfFreedome { Float rest_postion ; Float max_ang_limit, min_ang_limit; Int axis; Int LIM[4][4]; ////////////////////////////////////////////////////////////////////////////////////// Void set_flex_pramaeter (float x) { rest_postion = (max_ang_limit + min_ang_limit ) * x ; } }

Approach of this paper The sliding Axis Joint Case ▫This approach use an evoluta ▫Every time the angular parameter of a Dof changes, the same parameter is used in the curve equations to determine its respective point on the curve. Then, the axis is translated to the calculated point

The Pseudo-code : for the basic model Create the human body as a tree node Initialize the LIM matrix with the relationship of a child & a parent joint Define each joint into its parent reference frame Create a graphic object for each joint Initialize the LIM object matrix with object position in relation to the associated joint Generate GIM matrix Initialize GIM by multiplying the LIM joints from the root to the current joint with the object LIM Define the DOF of each joint

The Pseudo-code : for the sliding Axis Joint IF DOFAngle ! = currentAngle THEN Calculate the new point of the curve Translate the axis to the new point END IF

The Pseudo-code : for the relations between two joints IF DOFAngle1 != currentAngle1 && DOFAngle2 != currentAngle2 THEN Calculate the new DOFAngle using the DOFAngle2 and DOFAngle1 Update the currentAngle1 by the new DOFAngle END IF

Achievements of the Proposed Solution The achievements were ▫ the ability to represent the all types of human joints ▫sliding axis approach ▫a mechanism to represent interference of one joint position and orientation in the motion ranges of others

Comparison between this model & other models ComparisonModels There are some limitations in the SIMM model which is the absence of some motion axis, the absence of menisci, and the very low resolution of the mesh that represents the bones. Simulation System SIMM There is a great similarity in the patella motion and the terminal rotation.Plastic Knee We find a great similarity between them Internal view of the real living knee

The Weakness of this model A lack in the validation process was the impossibility of measuring the geometry of the models used in the comparison, and the angles of the performed movements If that was possible, they could probably reproduce specific geometry and motion for the models, yielding better comparison

Conclusion