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An OpenSim model represents the neuromuscular and musculoskeletal dynamics of a human or animal that is of interest to study within a computer simulation. The OpenSim model is made up of components corresponding to parts of the physical system that combine to generate or describe movement. These parts are: reference frames, bodies, joints, constraints, forces, contact geometry,   markers and controllers

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Code Block
languagexml
titleExample XML Code from Model Arm26 to Represent a Body
<Body name="r_humerus">
	<attached_geometry>...</attached_geometry>
	<WrapObjectSet>...</WrapObjectSet>
	<mass>1.8645719999999999</mass>
	<mass_center>0 -0.18049599999999999 0</mass_center>
	<inertia>0.01481 0.0045510000000000004 0.013193 0 0 0</inertia>
</Body>

Every model comes with a Ground body, which exists as a property of a Model, not in the BodySet.

Geometry

In version 4.0, OpenSim supports more types/shapes than in previous versions. You don't have to specify a mesh file to use most analytical shapes (Brick, Sphere, Cylinder, Cone, Ellipsoid). In addition you can specify Mesh to indicate geometry read from a mesh file. You can use .vtp, .stl, or .obj files to visualize geometry. All these types are kinds of Geometry. Check the units of your model and the units of the exported geometry (e.g., from Solidworks) if you are experiencing size/display issues. 

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