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Comment: Clarify expected data from IMUs

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Once you have collected and pre-processed your data, you must convert it to OpenSim's file format and associate it with an OpenSim model. Data from IMUs can be in various formats: a single file with numbered sensor names (e.g., APDM) or multiple files with sensor-specific numbering (e.g., Xsens). Upon import, OpenSim will create a single, time synced, Storage (.sto) file format for orientations, converting the rotation matrices into quaternions. 

In this example, we will be using data from an Xsens system that has been pre-processed (e.g., time-syncing and sensor fusion has been performed)  and exported to an Xsens text format. You can find this data in the IMUData folder. Each Xsens sensor is represented by a single text (.txt) file with time histories of the internal sensor data. We assume the data reported by the IMU system to include orientations (in the case of XSens these are assumed to be direction-cosine-matrices).

To read your data, you first need to create a file that lets OpenSense know which sensor is associated with which body segment in the Model. In our example, this file is called myIMUMappings.xml. You can open and edit this file in any text editor. In this settings/XML file you specify the following information:

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