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--- visual3d:documentation:modeling:segments:segment_overview [2024/11/03 17:08] – [Examples] wikisysop
+++ visual3d:documentation:modeling:segments:segment_overview [2025/03/12 21:53] (current) – Started the clean-up. wikisysop
@@ Line 3: / Line 3: @@
 A Visual3D model consists of a set of rigid segments, each of which corresponds to a body segment (major bone structure) of the subject whose motion is under study. We use the terms model segment and body segment when it is necessary to distinguish between the conceptual/mathematical segments of a Visual3D model and the corresponding physical body segments of the subject. Most of the time, we will simply say ”segment” when the distinction is clear from context.
-The instantaneous position and orientation of all a segment is called the pose of the segment. The central function of Visual3D is translation of the target-marker positions (as reported by the motion-tracking apparatus) into the pose of the corresponding model. Two factors complicate this process:
+The instantaneous position and orientation of all a segment is called the pose of the segment. The central function of Visual3D is translation of the target-marker positions (as reported by the motion-tracking apparatus) into [[visual3d:documentation:kinematics_and_kinetics:pose_estimation|the pose of the corresponding model]]. Two factors complicate this process:
+  - The motion-tracking apparatus does not track segments; it tracks target markers attached to various chosen points on or near the subject’s body.
-The motion-tracking apparatus does not track segments; it tracks target markers attached to various chosen points on or near the subject’s body. 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.
+  - 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 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.\\
+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.
-The illustration below shows what you might see when defining just one segment—the right thigh. The graphic image, which is zoomed in to the right thigh region, reveals three calibration markers (yellow) which are used to define the thigh segment’s endpoints and dimensions. At the proximal (upper) end, the RHP (right hip) marker’s position is used together with an explicit radius of 0.081m (measured in the laboratory for this subject) to define the proximal endpoint. At the distal end, both medial and lateral knee markers (RMK, RLK) are available, and together define both the distal endpoint and the distal radius of the thigh segment. For mass- and moment-related computations, this segment is modeled as a truncated cone (this is one of many details you provide under the Segment Properties tab) and so both proximal and distal radii are needed.
-{{:AnnotatedModel.gif}}\\
-==== Segments ====
-=== Standard Anatomical Conventions ===
-The Visual3D model-building tool uses standard medical terminology to define the locations and configurations of segments.
+The illustration below shows what you might see when defining just one segment: the right thigh. The graphic image, which is zoomed in to the right thigh region, reveals three calibration markers (yellow) which are used to define the thigh segment’s endpoints and dimensions. At the proximal (upper) end, the RHP (right hip) marker’s position is used together with an explicit radius of 0.081m (measured in the laboratory for this subject) to define the proximal endpoint. At the distal end, both medial and lateral knee markers (RMK, RLK) are available, and together define both the distal endpoint and the distal radius of the thigh segment. For mass- and moment-related computations, this segment is modeled as a truncated cone (this is one of many details you provide under the Segment Properties tab) and so both proximal and distal radii are needed.
-=== Default Segment Names ===
-[[visual3d:documentation:modeling:segments:segment_default_names]]
+{{:AnnotatedModel.gif}}
-Visual3D provides general modeling tools that allow for the creation of any rigid segments. For convenience, we have pre-defined the properties of common segments, such as the foot, shank etc. The properties of these segments are explicit, and the user can modify the properties.
+===== Segments =====
-=== Default Joint Names ===
-[[visual3d:documentation:pipeline:model_based_data_commands:default_joint_names]]
+The Visual3D model-building tool uses standard medical terminology to define the locations and configurations of segments. As a general modelling tool, Visual3D allows for the creation of any rigid segment. Visual3D contains a number of [[[[visual3d:documentation:modeling:segments:segment_default_names|default segment names]] that are provided for the convenience of the user. These default segments contain geometry, the inertial properties, and the wire frame model. Users that create their own segment names need to add this information in the segment properties tab in Model Builder Mode. Visual3D also creates [[visual3d:documentation:pipeline:model_based_data_commands:default_joint_names|joint names]] automatically for the default segments.
-Visual3D creates joint names automatically for the default segments.
+==== Virtual Segments ====
-Visual3D contains a number of default segment names that are provided for the convenience of the user. These default segments contain geometry, the inertial properties, and the wire frame model. Users that create their own segment names need to add this information in the segment properties tab in Model Builder Mode
-=== Virtual Segments ===
-[[visual3d:documentation:modeling:segments:virtual_segments]]
+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.
-We have grown accustomed to referring to Kinematic Only Segments as 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 Inverse Dynamics calculations. These segments can not be assigned external forces and will not have Joints created at their proximal end points.
 ==== Joints ====
-The term [[Visual3D:Documentation:Kinematics_and_Kinetics:Joint|Joint]] is used periodically throughout Visual3D, and has several different meanings. This tutorial focuses on a joint that connects two kinetic segments.
+The term [[Visual3D:Documentation:Kinematics_and_Kinetics:Joint|joint]] is used periodically throughout Visual3D, and has several different meanings. This tutorial focuses on a joint that connects two kinetic segments.
 In [[Visual3D:Documentation:Kinematics_and_Kinetics:Six_Degrees_of_Freedom|6 DOF]] tracking there is no explicit linkage (or joint) connecting the segments. Visual3D explores the collection of segments and considers any two segments in proximity (the distal end of one segment and the proximal end of another segment within the radius of the segment ends) to be "linked" and references a **//Joint//** between them. The **//Joint//** does not constrain the segments, but is rather a bookkeeping tool that keeps track of which segments are assumed to have an equal and opposite Joint Reaction Force acting between their endpoints and an equal and opposite Joint Moments acting on the adjacent segments.