Contributions:XsensMTwLogger: Difference between revisions
Wengelhardt (talk | contribs) Implementation of XSensMTwLogger |
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===MTw1X, MTw1Y, MTw1Z=== | ===MTw1X, MTw1Y, MTw1Z=== | ||
The three rotational data values recorded per MTw. See the “Coordinate System” section to see how X, Y, and Z are defined. If more than one MTw is connected, their label will continue to increase by 1, i.e. MTw2X, MTw3X, etc . | The three rotational data values recorded per MTw. See the “Coordinate System” section to see how X, Y, and Z are defined. If more than one MTw is connected, their label will continue to increase by 1, i.e. MTw2X, MTw3X, etc . The MTw’s connect in order of lowest serial code to highest serial code, so MTw1 will always have the lowest serial code number. The serial codes and their respective id’s are printed in the operator log for clarity’s sake. | ||
The MTw’s connect in order of lowest serial code to highest serial code, so MTw1 will always have the lowest serial code number. The serial codes and their respective id’s are printed in the operator log for clarity’s sake. | |||
==Converting back to Degrees== | ==Converting back to Degrees== | ||
Revision as of 20:58, 13 July 2021
An BCI2000 extension that records synchronized rotational data into states, using XSens’s MTw motion tracking sensors.
Location
http://www.bci2000.org/svn/trunk/src/contrib/Extensions/XSensMTwLogger
Versioning
Authors
Alex Belsten (belsten@neurotechcenter.org)
William Engelhardt (engelhardt@neurotechcenter.org)
Version History
- 2021-07-06: Initial public release by Alex Belsten (belsten@neurotechcenter.org)
Source Code Revisions
- Initial development: 6329
- Tested under: 6329
- Known to compile under: 6330
- Broken since: --
Functional Description
Records the X, Y, and Z positions of multiple Xsens MTw (Motion Tracking - wireless) IMUs (Inertial Measurement Units) to events.
Integration into BCI2000
To enable the extension in your CMake configuration, enable EXTENSIONS_XSENSMTWLOGGER=On in the Extensions folder of the CMake GUI and then generate the BCI2000 Visual Studio solution in CMake. Next, open the solution with Visual Studio and rebuild the BCI2000FrameworkSigSrcModule, and then rebuild any signal source module you want to use the extension with.
Once the extension is built into the source module, you can enable it by appending --LogXsensMTw=1 to the source module start executable command in your batch file. Also, --NumberOfMTws=1 needs to be appended as well. Set this equal to the exact number of MTw's you want connected.
Installation and Set-Up
To install the drivers for the MTw Awinda, go to their Software Downloads Page and download the latest stable software package for your operating system for "MTw Awinda". This installs the needed drivers; now BCI2000 can connect to the MTw's. Mtw's are wireless, so plug in one of the signal receivers provided into your USB port to be able to receive the signal. This receiver should be blinking in sync with the MTw's when they are recording.
Coordinate System
In the figure below, the orange rectangle is the MTw. Three axes are defined, the X, Y, and Z. X and Z range from -180 to 180 degrees, while Y spans from -90 to 90. All three coordinates are rotational, which means MTw’s do not directly measure translational movement.
Parameters
User configurable Parameters
The motion trackers are configured in the Source tab within the MTw section.
LogXsensMTw
Set to 0 (uncheck) to disable the MTw logger, or 1 (checked) to enable the logger. This should be set in your batch file by appending --LogXsensMTw=1 to the source module start executable command.
NumberOfMTws
The exact number of MTw's that will be connected. 1 is the default, but this number can go up to as many MTw's as you have. This parameter needs should be set in your batch file by appending --NumberOfMTws=1, just as LogXsensMTw is. It also doesn't appear in the Source tab, but rather can only be set in the batch file.
MasterUpdateRate
A default value of 80 Hz. This is the frequency that data is updated from the MTw’s to BCI2000. Below is a table provided by their MTw Awinda User Manual of the maximum update rates relative to the number of MTw’s connected.
| Amount of MTw’s | Update Rate (Hz) |
|---|---|
| 1-5 | 120 |
| 6-9 | 100 |
| 10 | 80 |
| 11-20 | 60 |
| 21-32 | 40 |
DataPrescaler
A default value of 10,000,000. The most efficient prescaler is 11,930,464, but for simplicity’s sake this value is rounded. Details about what this value does is located in “Converting Back to Degrees” below.
State Variables
MTw1X, MTw1Y, MTw1Z
The three rotational data values recorded per MTw. See the “Coordinate System” section to see how X, Y, and Z are defined. If more than one MTw is connected, their label will continue to increase by 1, i.e. MTw2X, MTw3X, etc . The MTw’s connect in order of lowest serial code to highest serial code, so MTw1 will always have the lowest serial code number. The serial codes and their respective id’s are printed in the operator log for clarity’s sake.
Converting back to Degrees
The MTw’s record data in units of degrees, with two of the axes going up to 180, and the other going to 90. They also record a high precision of 6 decimal places. BCI2000 records integers to states, which means that anything after the decimal point will be cut off. If the data is kept as is, this would greatly reduce the quality of the data we are collecting.
BCI2000 can record states with up to 32 bits, which is the resolution we need to record the high quality data from the MTw’s. To do this, the original data will be multiplied by the parameter DataPrescaler, and shifted up by 2^31.
To convert the data back into degrees, use Matlab or a similar program to
- Subtract 2^31 from every value.
- Divide the data by the
DataPrescaler.
This should now leave you with data between -180 and 180!