Point Modeling
Up ] [ Point Modeling ] Segment Modeling ] Segment Group Modeling ] Joint Modeling ]


The first step in body modeling is to define the points. Points can be classified into two groups: primary points and secondary points. Primary points are those to be digitized while secondary points are those to be computed based on the coordinates of the primary points. The joint centers are the typical secondary points. Secondary points are necessary when markers are attached to the body surface in a 3-D analysis since it is impossible to locate markers at the joint centers. If the image plane coordinates of the joint centers are to be obtained directly from manual digitizing, they must be defined as primary points.

One question here is how to compute the coordinates of the secondary points defined. There are two possible ways: (1) using the joint center computation algorithm described in the Computation of the Joint Center in the Joint Kinematics section, and (2) adding additional programs that specifically compute the coordinates of the secondary points. Method 2 is more complex because the computation algorithm may be study-specific so that one will need different add-on programs for different studies. Method 1 can be incorporated in a standard motion analysis program thus discarding the need to add the add-on programs.

In Kwon3D, a point can have the following properties:

Name: generic name of the point
Description: details about the point
Type: primary or secondary
Color: point color to be used in the stick-figure graphics
Connected-Points List: points to be connected to the current point in the stick-figure graphics
Connected Point: each previously defined point connected to this point
Line Color: each line color

The stick-figure graphics requires the information about how to connect the points. The connected-point list will sufficiently provide this information. Several points can be connected to the current point in the stick-figure graphics. The stick-figure graphics is very useful at least in the digitizing process. More sophisticated graphics can be added in the later stages for more effective feedback and presentation.


Young-Hoo Kwon, 1998-