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--- visual3d:documentation:pipeline:model_based_data_commands:cop_path [2024/06/19 12:51] – sgranger
+++ visual3d: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
@@ Line 1: / Line 1: @@
-{{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.
+===== COP Path =====
-by default, normalization is by segment width and length.
+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.
-===== model based item =====
+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:
-modelbasedcop_path.png
+{{:ModelBasedCop_Path.png}}
-===== pipeline command =====
-**compute_model_based_data**
+==== Normalization ====
-/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.
+Four options exist to normalize the computed value for the joint moment.
-===== sign convention =====
+  - Normalization Off: The computed value is not normalized.
+  - Normalize using default normalization: The computed value is normalized according to the segment width and length.
+  - 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.)
+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)
-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.
+==== The Right-Hand Rule ====
-this is described in this tutorial:
+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.
-[[visual3d:tutorials:kinematics_kinetics:model_based_computations#understanding_the_knee_angle_signal|tutorial:_model_based_computations#understanding_the_knee_angle_signal]]
+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]].
-===== 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.
+==== Example: a foot segment parallel to the floor ====
-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.
+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:
-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.
+Given a Left Foot gegment defined as:
-an axial value greater than 1 would mean that the cop was more distal than the metatarsals (e.g. under the toes)
+<code>
+Segment Name= Left Foot
-===== example: a foot segment parallel to the floor =====
+Define Proximal Joint and Radius
+Lateral= LLA Joint= none Medial= LMA
-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:
+Define Distal Joint and Radius
+Lateral= LMET5 Joint= none Medial= LMET1
-given a left foot segment defined as:
+Extra Target To Define Orientation (if needed)
+Location Lateral= none
+Select Tracking Markers: LFT1 LFT2 LFT3
+</code>
-segment name= left foot
+Create [[visual3d:documentation:modeling:landmarks:landmarks_overview|landmarks]] by projecting the anatomical markers used to define the foot onto the floor of the laboratory.
-define proximal joint and radius
-lateral= lla joint= none medial= lma
-define distal joint and radius
-lateral= lmet5 joint= none medial= lmet1
-extra target to define orientation (if needed)
-location lateral= none
-select tracking markers
-lft1 lft2 lft3
-\\
-'**create landmarks** by projecting the anatomical markers used to define the foot onto the floor of the laboratory.
-landmark name= lla_floor
+<code>
-define orientation using
+Landmark Name= LLA_FLOOR
-starting point=
+Define Orientation Using
-existing segment= lab
+Starting Point=
-offset using the following ml/ap/axial offsets
+Existing Segment= LAB
-x= lla::x y= lla::y z= 0
+Offset Using the Following ML/AP/AXIAL Offsets
-calibration only landmark= checked
+X= LLA::X Y= LLA::Y Z= 0
-landmark name= lma_floor
+Calibration Only Landmark= Checked
-define orientation using
-starting point=
-existing segment= lab
-offset using the following ml/ap/axial offsets
-x= lma::x y= lma::y z= 0
-calibration only landmark= checked
-\\
+Landmark Name= LMA_FLOOR
+Define Orientation Using
+Starting Point=
+Existing Segment= LAB
+Offset Using the Following ML/AP/AXIAL Offsets
+X= LMA::X Y= LMA::Y Z= 0
+Calibration Only Landmark= Checked
-landmark name= lmet5_floor
+Landmark Name= LMET5_FLOOR
-define orientation using
+Define Orientation Using
-starting point=
+Starting Point=
-existing segment= lab
+Existing Segment= LAB
-offset using the following ml/ap/axial offsets
+Offset Using the Following ML/AP/AXIAL Offsets
-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
+Define Orientation Using
+Starting Point=
+Existing Segment= LAB
+Offset Using the Following ML/AP/AXIAL Offsets
+X= LMET1::X Y= LMET1::Y Z= 0
+Calibration Only Landmark= Checked
+</code>
-landmark name= lmet1_floor
-define orientation using
-starting point=
-existing segment= lab
-offset using the following ml/ap/axial offsets
-x= lmet1::x y= lmet1::y z= 0
-calibration only landmark= checked
-\\
+Define the virtual foot segment as follows:
-**virtual foot segment**
+<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
-lateral= lmet5_floor joint= none medial= lmet1_floor
-extra target to define orientation (if needed)
-location lateral =none
-select tracking markers
-lft1 lft2 lft3
-\\
+Define Distal Joint and Radius
+Lateral= LMET5_FLOOR Joint= none Medial= LMET1_FLOOR
-create the center of pressure signal as shown in the dialog above.
+Extra Target To Define Orientation (if needed)
+Location Lateral= none
+Select Tracking Markers: LFT1 LFT2 LFT3
+</code>
-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.
-}}