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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.

References

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 The name of the base coordinates system the moving marker is defined in. Yes
biasCompensation false Switch bias compensation on or off. No
biasCompensationIterations 3 If bias compensation is used with this attribute the number of iterations can be defined. No
biasCompensationMaximumChange 10 If bias compensation is used and the different between the last two iteration is bigger than the given value in at least one component a warning is given. No
Condition A formula, which defines which frames are included in the functional calibration. If the formula value is 1 the frame is used. No
phase The name of the phases used for functional calibration. If this and the attribute Condtion are both not used the complete trials are used. 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>Radius Double Radius of the estimated sphere.
<name>FramesCount Integer Number of frames used for calibration.
<name>RadiusStd Double Std of the estimated radius of the sphere.

Comments

  • The current implementation is limited to cosider only one „moving“ marker.

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.

CoRChang2006

Attributes

Attribute Default Description Required
name name of the element Yes
coordinateSystem The name of the base coordinates system the moving marker is defined in. Yes

CoRNewton

Attributes

Attribute Default Description Required
name name of the element Yes
coordinateSystem The name of the base coordinates system the moving marker is defined in. Yes

Axis of rotation estimation

AoRChang2007

Attributes

Attribute Default Description Required
name name of the element Yes
coordinateSystem The name of the base coordinates system the moving marker is defined in. Yes

AoRGamage2002

Attributes

Attribute Default Description Required
name name of the element Yes
coordinateSystem The name of the base coordinates system the moving marker is defined in. Yes

AoRSARA

Attributes

Attribute Default Description Required
name name of the element Yes
coordinateSystem The name of the base coordinates system the moving marker is defined in. Yes
modellingcomponents/functionalmethods.txt · Zuletzt geändert: 2018/01/22 09:25 von oliver