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visual3d:documentation:pipeline:model_based_data_commands:cop_path [2024/07/03 17:42] – created sgrangervisual3d:documentation:pipeline:model_based_data_commands:cop_path [2024/11/05 16:06] (current) – Clean up page and brought it in line with the Model-Based Item template. wikisysop
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-====== COP_Path ======+===== COP Path =====
  
-Creating a LINK_MODEL_BASED signal called the COP_PATH is a more general way to compute the center of pressure. The command checks all [[Visual3D:Documentation:Kinematics_and_Kinetics:External_Forces:Force_Assignment|force assignments to the specified segment]] and any force platform. The signal is then transformed (or resolved) into the specified local coordinate system). All occurrences (eg. all force platforms) are included to determine if the segment has been assigned to the force signal.+Creating a [[visual3d:documentation:visual3d_signal_types:link_model_based_data_type|LINK_MODEL_BASED]] signal called the COP_PATH is a general way to compute the center of pressure. This command checks all [[Visual3D:Documentation:Kinematics_and_Kinetics:External_Forces:Force_Assignment|force assignments to the specified segment]] and all force platforms, then resolves the resulting signal into the specified local coordinate system.
  
-By default, normalization is by segment width and length.+For example, to calculate the center of pressure path for the left foot with respect to the left virtual foot, choose LFT as your segment and Left Virtual Foot as your resolution coordinate system:
  
-==== Model Based Item ====+{{:ModelBasedCop_Path.png}}
  
-{{ModelBasedCop_Path.png}} +==== Normalization ====
-==== Pipeline Command ====+
  
-**Compute_Model_Based_Data** +Four options exist to normalize the computed value for the joint moment.
-/RESULT_NAME=RT_COP +
-/FUNCTION=COP_PATH +
-/SEGMENT=RFT +
-/REFERENCE_SEGMENT= +
-/RESOLUTION_COORDINATE_SYSTEM=RFT +
-/USE_CARDAN_SEQUENCE=FALSE +
-/NORMALIZATION=TRUE +
-/NORMALIZATION_METHOD=DEFAULT_NORMALIZATION +
-/NORMALIZATION_METRIC= +
-! /NEGATEX=FALSE +
-! /NEGATEY=FALSE +
-! /NEGATEZ=FALSE +
-! /AXIS1=X +
-/AXIS2=Y +
-! /AXIS3=Z +
-**;** +
-==== Resolution Coordinate System ====+
  
-The coordinate system used by the model based items is precisely the coordinate system you see in the animation viewer. The length of the segment is defined from the proximal end to the distal end of the segment regardless of what axis you call this, and the proximal and distal radius are defined by the segment definition. +  - Normalization Off: The computed value is not normalized. 
- +  - Normalize using default normalization: The computed value is normalized according to the segment width and length. 
-==== Sign Convention ==== +  - Normalize to local file metric value: The user specifies the METRIC value in the local file with which to normalize the computed value. 
- +  - Normalize to global metric value: The user specifies the METRIC value in the GLOBAL workspace with which to normalize the computed value.
-As mentioned in the previous answer you can't really set up Abd and ExtRot so they have the same sign on both sides because Visual3D strictly follows the right hand rule. (This is done by design because some Visual3D users analyse things other than people/animals and thus the terms flexion/extension, ab/aduction and axial rotation have no meaning to them. Thus we simply always following the right hand rule to supply consistency for all users.) +
- +
-In order to get the signs of the COP_PATH to be consistent between the left and right leg (e.g. how to get around the fact that Visual3D enforces the right hand rule), you can select the check boxes in the dialog to negate one or more components. +
- +
-This is described in this tutorial: +
- +
-[[Visual3D:Tutorials:Kinematics_Kinetics:Model_Based_Computations#Understanding_the_Knee_Angle_Signal|Tutorial:_Model_Based_Computations#Understanding_the_Knee_Angle_Signal]] +
-==== Normalization ====+
  
-The standard normalization is relative to length (distance between proximal and distal ends of the segment) and width (distal radius) of the segment that is assigned to the force vector.+Note that the default normalization is relative to length (distance between proximal and distal ends of the segment) and width (distal radius) of the segment that is assigned to the force vector. If the foot segment defined from the ankle to the metatarsals is assigned to the force, then the range of motion might be on the order -1 to 2 in the axial direction, which may seem strange for a normalized value. In this case a negative axial value means the COP is behind the ankle and a positive axial value means the COP is in front of the ankle joint center. An axial value greater than 1 would mean that the COP was more distal than the metatarsals (e.g. under the toes)
  
-If the foot segment is assigned to the force, and the foot segment is defined from the ankle to the metatarsals, that range of motion might be on the order -1 to 2 in the axial direction, which may seem strange for a normalized value.+==== The Right-Hand Rule ====
  
-A negative axial value means the COP is behind the ankle and a positive axial value means the COP is in front of the ankle joint center.+It is not quite possible to set up model-based items so that their components have the same sign on both sides of the body because Visual3D strictly follows the right hand rule. This is done by design because some Visual3D users analyse things other than people/animals where the terms flexion/extension, ab/aduction and axial rotation have no specific meaning.
  
-An axial value greater than 1 would mean that the COP was more distal than the metatarsals (e.g. under the toes)+In order to get the signs of the COP_PATH to be consistent between the left and right leg, i.e., to get around the fact that Visual3D enforces the right-hand rule, you can select the check boxes in the dialog to negate one or more components. This process is described in [[Visual3D:Tutorials:Kinematics_and_Kinetics:Model_Based_Computations#Understanding_the_Knee_Angle_Signal|the tutorial explaining Knee Angle Signals]].
  
 ==== Example: a foot segment parallel to the floor ==== ==== Example: a foot segment parallel to the floor ====
  
-Commonly the center of pressure is computed relative to a ”r;special” foot coordinate system. A virtual foot is created that lies flat on the floor during the standing trial. The center of pressure is often scaled to the length and width of the foot segment. The following process can be used to create this signal:+Commonly the center of pressure is computed relative to a "special" foot coordinate system. A virtual foot is created that lies flat on the floor during the standing trial. The center of pressure is often scaled to the length and width of the foot segment. The following process can be used to create this signal:
  
-Given a Left Foot Segment defined as:+Given a Left Foot gegment defined as:
  
 +<code>
 Segment Name= Left Foot Segment Name= Left Foot
 +
 Define Proximal Joint and Radius Define Proximal Joint and Radius
 Lateral= LLA Joint= none Medial= LMA Lateral= LLA Joint= none Medial= LMA
 +
 Define Distal Joint and Radius Define Distal Joint and Radius
 Lateral= LMET5 Joint= none Medial= LMET1 Lateral= LMET5 Joint= none Medial= LMET1
 +
 Extra Target To Define Orientation (if needed) Extra Target To Define Orientation (if needed)
 Location Lateral= none Location Lateral= none
-Select Tracking Markers +Select Tracking Markers: LFT1 LFT2 LFT3 
-LFT1 LFT2 LFT3 +</code> 
-\\ + 
-'**Create Landmarks** by projecting the anatomical markers used to define the foot onto the floor of the laboratory.+Create [[visual3d:documentation:modeling:landmarks:landmarks_overview|landmarks]] by projecting the anatomical markers used to define the foot onto the floor of the laboratory.
  
 +<code>
 Landmark Name= LLA_FLOOR Landmark Name= LLA_FLOOR
 Define Orientation Using Define Orientation Using
Line 75: Line 54:
 X= LLA::X Y= LLA::Y Z= 0 X= LLA::X Y= LLA::Y Z= 0
 Calibration Only Landmark= Checked Calibration Only Landmark= Checked
 +
 Landmark Name= LMA_FLOOR Landmark Name= LMA_FLOOR
 Define Orientation Using Define Orientation Using
Line 82: Line 62:
 X= LMA::X Y= LMA::Y Z= 0 X= LMA::X Y= LMA::Y Z= 0
 Calibration Only Landmark= Checked Calibration Only Landmark= Checked
-\\ 
- 
  
 Landmark Name= LMET5_FLOOR Landmark Name= LMET5_FLOOR
Line 92: Line 70:
 X= LMET5::X Y= LMET5::Y Z= 0 X= LMET5::X Y= LMET5::Y Z= 0
 Calibration Only Landmark= Checked Calibration Only Landmark= Checked
-\\ 
- 
  
 Landmark Name= LMET1_FLOOR Landmark Name= LMET1_FLOOR
Line 102: Line 78:
 X= LMET1::X Y= LMET1::Y Z= 0 X= LMET1::X Y= LMET1::Y Z= 0
 Calibration Only Landmark= Checked Calibration Only Landmark= Checked
-\\+</code>
  
  
-**Virtual Foot Segment**+Define the virtual foot segment as follows:
  
 +<code>
 Segment Name= Left Virtual Foot Segment Name= Left Virtual Foot
 +
 Define Proximal Joint and Radius Define Proximal Joint and Radius
 Lateral= LLA_FLOOR Joint= none Medial= LMA_FLOOR Lateral= LLA_FLOOR Joint= none Medial= LMA_FLOOR
 +
 Define Distal Joint and Radius Define Distal Joint and Radius
 Lateral= LMET5_FLOOR Joint= none Medial= LMET1_FLOOR Lateral= LMET5_FLOOR Joint= none Medial= LMET1_FLOOR
 +
 Extra Target To Define Orientation (if needed) Extra Target To Define Orientation (if needed)
-Location Lateral =none +Location Lateral= none 
-Select Tracking Markers +Select Tracking Markers: LFT1 LFT2 LFT3 
-LFT1 LFT2 LFT3 +</code>
-\\ +
- +
- +
-Create the Center of Pressure signal as shown in the dialog above. +
- +
-Assuming the left foot segment has been assigned to a force platform. The segment is specified as the LFT. Visual3D interprets this as finding the contacts of the LFT segment on any of the force platforms. The resolution coordinate system is defined as the ”r;Left Virtual Foot” segment coordinate system, which is flat on the ground during standing posture. Normalization scales the COP_PATH signal to the length and width of the foot. This signal will appear in the data tree in the LINK_MODEL_BASED folder, and is available for graphing in the report. +
- +
  
 +Create the Center of Pressure signal as shown in the dialog above. Assuming the left foot segment has been assigned to a force platform and that the segment is specified as the LF,. Visual3D interprets this as finding the contacts of the LFT segment on any of the force platforms. The resolution coordinate system is defined as the "Left Virtual Foot" segment coordinate system, which is flat on the ground during standing posture. Normalization scales the COP_PATH signal to the length and width of the foot. This signal will appear in the data tree in the LINK_MODEL_BASED folder, and is available for graphing in the report.
visual3d/documentation/pipeline/model_based_data_commands/cop_path.1720028524.txt.gz · Last modified: 2024/07/03 17:42 by sgranger