===== Model COG Velocity =====

This model-based item represents the velocity of the [[visual3d:documentation:pipeline:model_based_data_commands:model_cog|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]].

To express the MODEL COG VELOCITY item in the [[visual3d:documentation:definitions:laboratory_coordinate_system|laboratory coordinate system]], choose the LAB segment as the resolution coordinate system. The Treadmill Data section of the dialog allows the user to account for the direction and speed of the treadmill's belt.

{{:model_cog_vel_dialog.png}}

==== Reasons for No Data ====

The velocity of the COG is calculated from the model's COG, which is the sum of the COM of all segments in the model. If a kinetic segment is missing during one frame then no COM can be calculated at that frame and [[visual3d:documentation:c3d_signal_types:data_not_found|NO_DATA]] will result.

As an additional factor, the MODEL COG VELOCITY model-based item was added in Visual3D v2022. If working with older CMZ files, it is necessary to [[visual3d:documentation:pipeline:general_information:recalc_pipeline|Recalc]] before running the Compute Model Based Data command since this creates the Kinetic_Kinematic::Model::CenterOfMassVelocity signal.

==== See Also ====

There is also a model-based item for [[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]].