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--- visual3d:documentation:pipeline:model_based_data_commands:model_cog [2024/06/19 14:01] – created sgranger
+++ visual3d:documentation:pipeline:model_based_data_commands:model_cog [2024/11/05 14:15] (current) – [MODEL COG] wikisysop
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+===== Model COG =====
-Model of Center of Gravity
+This model-based item represents the Center of Gravity of the entire model. This center of gravity is calculated by first calculating the center of mass of each kinetic segment and then calculating the center of mass across all of the model's kinetic segments according to [[https://en.wikipedia.org/wiki/Center_of_mass|mechanical principles patterns]].
-The center of mass of each segment is calculated as follows: https://www.c-motion.com/v3dwiki/index.php?title=Segment_Inertia
+To express the MODEL COG item in the [[visual3d:documentation:definitions:laboratory_coordinate_system|laboratory coordinate system]], choose the LAB segment as the resolution coordinate system.
-The default values, however, can be modified by the user to include any equation already published.
+{{:MODEL_COGdlg.jpg}}
-The center of mass of the model is the center of mass of the kinetic segments (only segments kinematics are not included). The calculation is based on mechanical principles patterns: http://en.wikipedia.org/wiki/Center_of_mass
+==== Centre of Mass for a Segment ====
-The degree to which the center of mass of the segments and the center of mass of the individual agree is based on how well the individual is represented. For example, if the model includes only the lower end, the center of mass of the segments will be different enough from the center of mass of the individual.
+Visual3D calculates the centre of mass for a segment according to that [[visual3d:documentation:modeling:segments:segment_inertia|segment's inertia]]. Visual3D provides default values for segment inertia, but these can be modified by the user to reflect any desired equation.
-{{MODEL_COGdlg.jpg}}
+[[visual3d:documentation:modeling:segments:virtual_segments|Kinematic-only (or virtual) segments]] are not included in the calculation of a model's center of gravity.
+==== Representativeness ====
+The degree to which the center of mass of a model's segments agree with the center of mass of the participant being modelled will depend on how well the individual is represented.
+For example, if the model includes only segments from the lower extremity then the center of mass of the segments will deviate substantially from the center of mass of the individual.
+==== See Also ====
+There are also model-based items for [[visual3d:documentation:pipeline:model_based_data_commands:model_cog_velocity|MODEL_COG_VELOCITY]] and [[visual3d:documentation:pipeline:model_based_data_commands:model_cog_acceleration|MODEL_COG_ACCELERATION]]. Or return to [[visual3d:documentation:visual3d_signal_types:link_model_based_data_type#kinematic_items|LINK_MODEL_BASED items]].