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modellingcomponents:functionalmethods

Functional joint center/axes estimation methods

The calculation of a functional joint is based on the movement of one segment relative to another segment. This allows to estimate knee- and elbow joint axes, hip- and glenohumeral joint centers.

The calibrations movements should have sufficient range of motion that the computation statistics produce a reasonable stationary point, but the range of motion should not be too large because soft tissue artifact (e.g. movement of markers relative to the underlying skeleton) should be minimized.

Typically specific calibration trials have to be executed.

Several cycles of movement should be included, but there is no study which analyses how many cycles is best. We recommend more than 3 cycles, others recomment a minimum of 5. The optimal number may depend on many issues, including the joint and the amount of soft tissue artfeacts. Each user should experiment with his own measurement procedure.

Centre of rotation estimation

References

A survey of formal methods for determining the centre of rotation of ball joints.
Ehrig RM, Taylor WR, Duda GN, Heller MO
J Biomech39p2798-809(2006)

CoRGamage2002

Attributes

Attribute Default Description Required
name name of the element Yes
coordinateSystem Yes
biasCompensation No
biasCompensationIterations 3 No
Condition
phase

Generated trajectories

Name Type
<name>Origin 3d vector

Generated parameters

Name Type Description
<name>OriginLocal 3d vector CoR in local coordinates of the parent system
<name>Radius Double radius of the estimated sphere
<name>FramesCount
<name>RadiusStd Double std of estimated radius of the sphere

References

Examples

<Phase name="RAbduk" startEvent="RHS" endEvent="RTO" process="post" 
       calibrateIncludes="dynamic_calibrate_right_shoulder"
       includes="dummy"/>
<CoRGamage2002 name="RGHJC"
               coordinateSystem="Right_Acromion"
               phase="RAbduk"
               biasCompensation="true"
               biasCompensationIterations="5"
               calibrateIncludes="dynamic_calibrate_right_shoulder"
               includes="dynamic,static">RHUMS</CoRGamage2002>
 

SCoRE - symmetrical centre of rotation estimation

Attributes

Attribute Description Required
name name of the element Yes
parentCoordinateSystem Yes
childCoordinateSystem Yes
condition If the attribute phase is not used and if it is set to a mathematical formula which is 1 or 0 it is used instead of defined events No
phase phase name, used if the phases are calculated elsewhere No

Generated trajectories

Name Type
<name>Origin 3d vector

Generated parameters

Name Type Description
<name>OriginLocal 3d vector CoR in local coordinates of the parent system
<name>FramesCount double count of frames used for the estimation
<name>Radius double radius of the sphere around the origin of the parent coordinate system on which the origin of the child coordinate system is assumed to move around.
<name>RadiusStd double standard deviation of the radien

References

A survey of formal methods for determining the centre of rotation of ball joints.
Ehrig RM, Taylor WR, Duda GN, Heller MO
J Biomech39p2798-809(2006)

Examples

   <CoRSCoRE name="RGHJC"
             condition="RAbdukAngle<30.0"
             parentCoordinateSystem="RClavicle"
             childCoordinateSystem="RHumerus"/>

Notes

A warining is given, if the count of frames selected by the defined phases is smaller than 30. Keep in mind that even 30 frames typically are too less to get a „good“ estimation of a center of rotation. In this case the frames of the complete trial are used, which also typically does not result in an good estimation.

modellingcomponents/functionalmethods.txt · Zuletzt geändert: 2017/04/04 11:54 von oliver