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--- visual3d:documentation:modeling:segments:segment_overview [2025/03/13 20:38] – wikisysop
+++ visual3d:documentation:modeling:segments:segment_overview [2025/04/03 12:29] (current) – Cleaned up the Foot section. wikisysop
@@ Line 7: / Line 7: @@
   - Segments are defined by (among other things) their proximal and distal end points, which are located inside the body, but target markers can generally only be placed outside the body.
-To deal with the first complication, Visual3D makes use of the notion of segment-relative coordinate systems (usually called simply segment coordinate systems or SCS). The idea is that although the motion-tracking apparatus reports marker positions by their laboratory or LCS coordinates, and in general all markers are moving, it can safely be assumed that the target markers move with the body segments to which they are attached, i.e., each target’s coordinates in the appropriate segment coordinate system (SCS) do not change throughout the movement. Provided at least three target markers, not positioned in a line, are tracked for each body segment, Visual3D will have enough information to determine the model pose.
+To deal with the first complication, Visual3D makes use of the notion of segment-relative coordinate systems (usually simply called the [[visual3d:documentation:modeling:coordinate_system|segment coordinate systems]] or SCS). The idea is that although the motion-tracking apparatus reports marker positions by their [[visual3d:documentation:definitions:laboratory_coordinate_system|laboratory]] or LCS coordinates, and in general all markers are moving, it can safely be assumed that the target markers move with the body segments to which they are attached, i.e., each target’s coordinates in the appropriate SCS do not change throughout the movement. Provided at least three target markers, not positioned in a line, are tracked for each body segment, Visual3D will have enough information to determine the model pose.
 To deal with the second complication, Visual3D allows you to define the precise spatial relationships between each segment’s proximal and distal endpoints and the positions of target markers. This process is normally facilitated by capturing the position of extra calibration markers placed at points which, though not suitable for use in motion tracking, provide clear information about the location of joint centers within the body. Note that the choice of where and how to place target markers is itself a significant subject.
@@ Line 43: / Line 43: @@
 Kinematic-only segments are also called [[visual3d:documentation:modeling:segments:virtual_segments|virtual segments]]. The defining criterion for distinguishing a virtual segment from other segments in Visual3D is that these segments do not get included in the [[visual3d:documentation:kinematics_and_kinetics:inverse_dynamics|Inverse Dynamics]] calculations. These segments can not be [[visual3d:documentation:kinematics_and_kinetics:external_forces:force_assignment|assigned external forces]] and will not have [[visual3d:documentation:kinematics_and_kinetics:joint|joints]] created at their proximal end points.
-===== The Pelvis, a segment of note =====
+===== The Pelvis =====
 There are many ways to define a segment in Visual3D, which means there are many ways to define the Pelvis segment.
@@ Line 55: / Line 55: @@
 **NOTE**: the segment coordinate system for the CODA pelvis is the mid-point between the ASIS markers. The anatomical landmarks are actually posterior to the ASIS markers because the motion capture system tracks the center of the marker. This is a modest error, but it can be corrected by [[visual3d:documentation:modeling:segments:create_coda_pelvis_relative_to_anatomical_landmarks|creating landmarks that are posterior to the ASIS markers by the radius of the motion capture marker]].
-==== Hip_Joint_Landmarks ====
+==== Hip Joint Landmarks ====
 [[visual3d:documentation:modeling:segments:hip_joint_landmarks|Regression equations]] have been estimated for calculating the position of common hip joint landmarks relative to the pelvis segment coordinate system.
-== Pelvis Animation Models (obj, v3g, wrl) ==
+==== Pelvis Animation Models (obj, v3g, wrl) ====
 There are two common obj files used to animate the bones of the pelvis.
-== Normalizing the Pelvis Angle ==
-[[visual3d:documentation:modeling:segments:normalizing_the_pelvis_segment_angle_example]]
-Normalizing the Pelvis Segment Angle. The Coda and Helen Hayes pelvis are tilted forward approximately 20 degrees from the horizontal.
+==== Normalizing the Pelvis Angle ====
-In describing the orientation of the pelvis or for describing the hip joint angle,
-it is often convenient to define a pelvis angle that has a coronal plane parallel to the floor (eg a vertical segment with zero tilt).
-===== Thigh =====
+The CODA and Helen Hayes pelvis models are tilted forward approximately 20 degrees from the horizontal. In describing the orientation of the pelvis or for describing the hip joint angle, it is often convenient to define a pelvis angle that has a coronal plane parallel to the floor, e.g. a vertical segment with zero tilt.
-There are several approaches to create a thigh segment in Visual3D. We have outlined a few for you on the linked pages that are found below.
+A demonstration of this is provided in our example of [[visual3d:documentation:modeling:segments:normalizing_the_pelvis_segment_angle_example|normalizing the pelvis segment angle]].
-==== Thigh using Greater Trochanter ====
+===== Thigh =====
-This page shows how to define the thigh segment using the greater trochanter as the proximal-lateral marker.
+There are several approaches to create a thigh segment in Visual3D, a few are outlined below.
-==== Thigh using Hip Joint Landmark ====
-[[#Create_Right_Thigh_Segment|Create Right Thigh Segment]] shows how to construct the right thigh segment based on the Hip Joint Landmark and medial/lateral knee markers.
+^ Approach ^ Description ^
-Another example can be found on [[Visual3D:Documentation:Modeling:Segments:Using_a_model_metric_in_an_expression|Segment Examples 2]]
+| Using the Greater Trochanter | A thigh can be [[visual3d:documentation:modeling:segments:thigh_using_greater_trochanter|defined]] using the greater trochanter as the proximal-lateral marker. |
-==== Using the Knee Alignment Device ====
+| Using Hip Joint Landmarks | A thigh segment can be [[visual3d:tutorials:modeling:building_a_6_dof_model#Create_the_Right_Thigh_Segment|constructed]] based on hip joint [[visual3d:documentation:modeling:landmarks:landmarks_overview|landmarks]] and medial/lateral knee markers. See also this [[Visual3D:Documentation:Modeling:Segments:Using_a_model_metric_in_an_expression|example]]. |
+| Using the Knee Alignment Device | A thigh can be [[visual3d:documentation:modeling:segments:knee_alignment_device#step_5create_a_right_thigh_segment|modelled]] using the Knee Alignment Device (KAD) manufactured by Motion Lab Systems. This approach uses the KAD to assist in defining the front plane of the thigh segment. |
-This page will create the thigh segment using a Knee Alignment Device. The Knee Alignment Device (KAD) is manufactured by Motion Lab Systems. The KAD is used to assist in defining the frontal plane of the thigh segment.
 ===== Shank =====
-[[Visual3D:Documentation:Modeling:Segments:Modeling_the_Shank|Example: Shank]]
+When modelling the shank it is possible to encounter difficulties related to tibial torsion. This can be [[[[Visual3D:Documentation:Modeling:Segments:Modeling_the_Shank|accomodated]] by defining two shank segments:
+  - one to calculate the knee joint angles; and
+  - the other to calculate the ankle joint angles.
-This page shows an example of accommodating for tibial torsion by defining two shank segments; using one to calculate the knee joint angles and the other to calculate the ankle joint angles.
 ===== Foot =====
-There are several approaches to creating segments at the foot. We illustrate a few below. The [[Visual3D:Tutorials:Kinematics_and_Kinetics:Foot_and_Ankle_Angles_|Tutorial: Foot and Ankle Angles]] page discusses the creation of segments at the foot and their angles. Several examples are shown: kinetic foot, heel-toe, Normalized to the proximal segment, and projected landmarks.
+There are several approaches to creating segments at the foot.
-==== Orthotrack Foot ====
+^ Model ^ Description ^
+| Oxford Foot | Our interpretation of the [[Visual3D:Tutorials:Modeling:Oxford_Foot_Model|Oxford foot model]] implemented in Vicon Nexus. |
+| IOR Foot | How to create the multi-segment [[[[Visual3D:Tutorials:Modeling:IOR_Foot_Model|IOR foot model]].|
+| OrthoTrack Foot | OrthoTrack's [[visual3d:documentation:modeling:segments:example_-_orthotrack_foot|foot model]].|
-This page shows an example of how Orthotrak defines the foot segment coordinate system.
-==== Oxford Foot ====
-[[Visual3D:Tutorials:Modeling:Oxford_Foot_Model|Tutorial: Oxford Foot Model]] is a tutorial on the oxford foot model.
+The [[Visual3D:Tutorials:Kinematics_and_Kinetics:Foot_and_Ankle_Angles_|Foot and Ankle Angles tutorial]] discusses general considerations for creating segments at the foot and computing associated joint angles. Several examples are shown, including:
-==== IOR Foot ====
+  - kinetic foot;
+  - heel-toe;
+  - normalized to the proximal segment; and
+  - using projected landmarks.
-[[Visual3D:Tutorials:Modeling:IOR_Foot_Model|Tutorial: IOR Foot Model]] shows how to create the multisegment IOR foot model.
 ==== Skeleton doesn't look right? ====