Xsens

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We have the Xsens MVN Biomech.

This is inertial sensors based full body motion capture equipment and consists of 17 sensors, which are attached to key areas of the human body. Each sensor consists of 3D gyroscopes, accelerometers and magnetometers.

Contents

MVN Studio (WIN)

The most straight forward way to use the Xsens system is with the MVN Studio software, which can be used to perform recordings, playback and advanced post-processing.

There exists two version, MVN Studio 2.6 and 3.0 (biomech). 2.6 is more specialized toward the animation industry while 3.0 contains more biomechanical analysis options. In the latter you can look at graphs of biomechanical data in recorded files.

Note: Recordings done in MVN Studio 3.0 can only be opened by 3.0. Since we only have 3 licenses (hardware locked) for MVN Studio 3.0, it may be better to do the recordings in MVN Studio 2.6. These recordings can be opened in both 2.6 and 3.0.

Output if the MVN Studio: The system outputs information about body motion by expressing body postures sampled at a rate up to 120Hz. The postures are modeled by 23 body segments interconnected with 22 joints. The system offer the information about the position, velocity, acceleration, orientation, angular velocity and angular acceleration of these segments.

Calibration

Before using Xsens you need to perform a calibration. This takes from 30 seconds to an hour depending on how precise one wants to be. We have found out that so-called N-pose and T-pose calibration are the most important. A hand touch calibration is recommended if a good relative position performance between the left and right hand is wanted. Refer to the tutorial files in Documentation\Tutorials in the Xsens folder for good video demonstrations on how to perform the calibrations.

MVN Studio network stream

MVN Studio 2.6 and 3.0 has the possibility to, in real time, stream the data over an UDP connection. To be able use this stream you need to decode the datagram’s packages. There are three data formats options for streaming: Body segments position and orientation either in Euler or Quaternion’s and an optical marker simulation stream.

We have implemented a simple (and slow) java mxj object for receiving the UDP datagram’s packages in MAX/MSP].

MVN Software Development Kit (SDK)

The Xsens SDK is a windows library which enables software to directly communicate with MVN engine. Xsens offer C++ examples files for Visual Studio.

MVN Export and Matlab

MVN Studio 3.0 can export recording as BVH, C3D, FBX and MVNX (2.6 do not support C3D export). There exists a toolbox for Matlab, the XML_IO_TOOL toolbox that can import MVNX files (XML based). Refer the Xsens MVN Biomech user manual section 18.16.2 page 118. The MoCap Toolbox can import the C3D files.

Note: The exported C3D files contains only position data from the MVN recordings (not acceleration, orientation, velocity etc.). The data are translated so that they look like a marker based optical motion capture files (based on 64 markes).

MT SDK for using "isolated" MTs

The MVN software demands a human body model to be able to track motions. If you want use isolated MT sensors, or track motions not connected to the human body, you will need to use the MT SDK.

OSC and Xsens

We have made two OSC implementations for the Xsens MVN system. These implementations can both stream real time data or recorded data to OSC applications.

1. We have made a simple terminal application that translates the UDP network packages (see above) from MVN Studio and resend the wanted data as OSC messages/bundles. In this way you can still benefit from the MVN Studio ease of use. However, the MVN Studio network stream suffers from frame losses when driven in real-time mode, making it a less ideal solution.

2. We have developed a simple terminal application with the SDK, which supports the basic Xsens features (calibration etc.). We have also implemented an internal function that can send the motion data in the same data format as the Network UDP Datagram stream. This stream can then be opened by MVN Studio (2.6 or 3.0) to get visual feedback of the MoCap data. This is our preferred implementation for real-time interaction use, since it offers more data directly from the MVN engine and does not suffer from frame loss.

For more help with using the Xsens system contact savskogs at ifi.uio.no.

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