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The Scale Tool alters the anthropometry of a model so that it matches a particular subject as closely as possible. Scaling is typically performed by comparing experimental marker data to virtual markers placed on a model. In addition to scaling a model, the Scale Tool can be used to adjust the locations of virtual markers so that they better match the experimental data.

The Scale Tool is accessed by selecting Tools → Scale Model… from the OpenSim main menu bar. Like all tools, the operations performed by the Scale Tool apply to the current model.

Overview

The figure below shows the required inputs and outputs for the Scale Tool. Each is described in more detail in the following sections.

Inputs and Outputs of the Scale Tool. Experimental data are shown in green; OpenSim files (.osim) are shown in red; settings files are shown in blue.

Settings Files

The subject01_Setup_Scale.xml file is the setup file for the Scale Tool. It contains settings, described in detail in How Scaling Works. The setup file can include the following information:

• ScaleTasks: Inverse kinematics tasks for the Scale Tool. In addition to scaling the model, the Scale Tool moves the virtual markers on the model so that their positions match the experimental marker locations. To do this, the Scale Tool must position the model so that it best matches the position of the subject. This requires an inverse kinematics problem to be solved. This file contains the inverse kinematics tasks describing which virtual and experimental markers should be matched up during the inverse kinematics phase. The file also contains marker weights, which are relative and determine how "well" the virtual markers track experimental markers (a larger weight will result in less error between the corresponding virtual and experimental marker positions).
• ScaleMeasurementSet: Measurement set for the Scale Tool. It contains pairs of experimental markers, the distance between which are used to scale the generic musculoskeletal model. 
• ScaleScaleSet Scale set for the Scale Tool. It contains a set of manual scale factors to be applied to the generic musculoskeletal model.

ScaleMarkerSet.xml: Marker set for the Scale Tool. It contains the set of virtual markers that are placed on the body segments of the model.

Inputs

Two data files are required by the Scale Tool:

subject01_static.trc: Experimental marker trajectories for a static trial. A static trial is usually several seconds of data with the subject posed in a known static position. A segment of a regular motion file can be used as a static trial if desired, but this is not typically done. The static pose should include the subject wearing the full marker set. The marker trajectories are specified in the global frame. You can find more information about collecting and preparing motion data in the section on Preparing Your Data.

gait2354_simbody.osim: OpenSim musculoskeletal model. This generic model will be scaled to match the anthropometry of your subject.

You can also provide an additional, optional file:

subject01_static.mot: Experimental generalized coordinate values (joint angles) for a trial obtained from alternative motion capture devices or other specialized algorithms. You can specify coordinate weights in the Tasks file, if joint angles are known a priori. Coordinate weights are also relative and determine how "well" a joint angle will track the specified angle.

Outputs

The Scale Tool generates a single file:

subject01_simbody.osim: OpenSim musculoskeletal model scaled to the dimensions of the subject.

Best Practices and Troubleshooting

Video Tutorials

Setting up the scale tool:

Evaluating your results: