Inverse Kinematics Tasks for Scale

The topics covered in this section include:

The inverse kinematics (IK) tasks file <IKTaskSet> referred to from the main Scale Setup File is shown in the example below. The IK tasks file specifies properties associated with error terms. A brief description of the tags used to describe these properties is given below. The section on Inverse Kinematics provides more details.

Marker Tasks

The <IKMarkerTask> tags are used to specify the weights associated with the marker error terms in the IK formulation. See the IK chapter (Inverse Kinematics) for more details.

Example: XML markup for an inverse kinematics tasks set

<IKTaskSet name="gait2354_Scale"> 

  <objects> 
    <IKMarkerTask name="Sternum"> <weight>1</weight> </IKMarkerTask> 
    <IKMarkerTask name="R.Acromium"> <weight>1</weight> </IKMarkerTask> 
    <IKMarkerTask name="L.Acromium"> <weight>1</weight> </IKMarkerTask> 
    <IKMarkerTask name="Top.Head"> <weight>1</weight> </IKMarkerTask> 
    <!– . . additional <IKMarkerTask> tags cut for brevity . . –> 

    <!– Coordinates –> 
    <IKCoordinateTask name="subtalar_angle_r"> <value>0</value> </IKCoordinateTask> 
    <IKCoordinateTask name="mtp_angle_r"> <value>0</value> </IKCoordinateTask> 
    <IKCoordinateTask name="subtalar_angle_l"> <value>0</value> </IKCoordinateTask> 
    <IKCoordinateTask name="mtp_angle_l"> <value>0</value> </IKCoordinateTask> 
    <IKCoordinateTask name="lumbar_extension"> 
    <value>0</value> 
    <weight>1000.0</weight> 
    </IKCoordinateTask> 

  </objects> 
</IKTaskSet> 

Coordinate Tasks

The <IKCoordinateTask> tags are optional and are used to specify properties associated with the coordinate error terms in the IK formulation. See the IK chapter (Inverse Kinematics) for more details. In the example above, the subtalar and mtp angles are locked, and are assigned to the constant value of 0 radians. Additionally, we have a task which attempts to keep the (unprescribed) lumbar_extension coordinate close to 0 by setting its desired value to 0 and giving it a large weight.