mvnx

The mvnx file format

The MVNX (Moven Open XML format) files contains 3D position, 3D orientation, (and optionally; 3D acceleration, 3D velocity, 3D angular rate, 3D angular acceleration) of each segment (not the sensors) in XML format (ASCII). The following documentation is extracted partially from the XSens original documentation and by review of example files. There are still open point with unknow undocumented behavoir.

<mvnx>

The MVNX file starts with a version number
<mvnx version="2">

General

The <mvnxInfo> section contains information about the number of frames, the frame rate, recording date, original MVN file, and the contents of velocity, acceleration, angular velocity or angular acceleration data.
<mvnxInfo frameCount="1000"
 frameRate="100"
 recDate="0"
 originalFilename="c:\data\session‐001.mvn"
 velData="1"
 accData="0"
 angVelData="1"
 angAccData="0"/>
Attribute Default description
frameCount
count of frames
frameRate
frames per second
recDate
Unknow format, e.g. 1239100243 recorded 2009
originalFilename
absolute path to the original ".mvn" file
velData
0

set to "1" if position velocity data is available
accData
0

set to "1" if position acceleration data is available
angVelData
0

set to "1" if angular velocity data is available
angAccData
0

set to "1" if angular acceleration data is available

Events (markers)

The section <markers> contains the description of markers with frame number and marker name if present. In comparison with nomenclature of Vicon Workstation, markers are events. But there are no event types. It seems to be allowed to define more than one marker with the same name (event type) in a trial. Instead of the common c3d-format the position of the marker is defined by an integer instead of a double defining a real time point with optional definition of a range.
<markers>
    <marker frame="123" name="RHS"/>
    <marker frame="340" name="RTO"/>
</markers>
For compatiblity the following table shows the Vicon workstation event type names and its meaning, which must be used for correct gait cycle detection also for the XSens system to be compatible with the Nimue-Platform applications.
marker (event) name description
RHS
right foot strike
LHS
left foot strike
RTO
right foot off
LTO
left foot off
LG
special meaning in the gaitlab heidelberg: 1. between LHS and LTO to indicate that the kinetics is usable, 2. if there are more then one of this events between LHS and LTO first and last LG event defines start and end of a foot flat phase of the left side
RG
special meaning in the gaitlab heidelberg: 1. between RHS and RTO to indicate that the kinetics is usable, 2. if there are more then one of this events between RHS and RTO first and last RG event defines start and end of a foot flat phase of the right side
GG
general event of no specific side

Comments

The section <comment> contains the text which has been entered when creating a new recording session.

Mesh scale

The <meshScale> data is used for scaling of the visualization of the character in Moven Studio.

Segment Points

The section <segments> defines all positions of connecting joints and anatomical landmarks with respect to origin of that segment (in body frame B).
<segment id="16" label="RightUpperLeg">
 <point label="jRightHip" pos_s="0.000000 0.000000 0.000000"/>
 <point label="jRightKnee" pos_s="0.000000 0.000000 ‐0.417462"/>
 ...
</segment>

Security code???

In some exported .mvnx-files a tag with unknow meaning is found:
<securityCode code="0639359e" />

Frames

The section <frames> contains the actual motion capture data. Each time frame consists of one row, containing 23 segments with 7 channels per segment (4 quaternion, 3 position) = 161 columns of data.

All kinematic data is expressed in the global coordinates system (with Z up).

Format of the data:

Sample 1 <F v=" ^GBq_seg1 ^Gpos_seg1 ^GBq_seg2^Gpos_seg2
…^GBq_seg23^Gpos_seg23" />

Sample 2 <F v=" ^GBq_seg1 ^Gpos_seg1 ^GBq_seg2^Gpos_seg2
…^GBq_seg23^Gpos_seg23" />

…

Sample n <F v=" ^GBq_seg1 ^Gpos_seg1 ^GBq_seg2^Gpos_seg2
…^GBq_seg23^Gpos_seg23" />

^GBq_seg is the quaternion (q₀, q₁, q₂, q₃) describing the rotation of the segment in the global frame

^Gpos_seg is the position (x,y,z) of the origin of the segment in the global frame

When kinematic data other than position and orientation have been selected in the preference menuthey will be written after the <frames> section:
<velocity>
	Sample 1 <F v=" Gvseg1 Gvseg2 … Gvseg23 " />
	Sample 2 <F v=" Gvseg1 Gvseg2 … Gvseg23 " />
	…
	Sample n <F v=" Gvseg1 Gvseg2 … Gvseg23 " />
</velocity>
<ang_velocity>
	Sample 1 <F v=" Gwseg1 Gwseg2 … Gwseg23 " />
	Sample 2 <F v=" Gwseg1 Gwseg2 … Gwseg23 " />
	…
	Sample n <F v=" Gwseg1 Gwseg2 … Gwseg23 " />
</ang_velocity>
Gvseg is the 1x3 velocity vector (x, y, z) of the origin of the segment in the global frame in [m/s].
Gwseg is the 1x3 angular velocity vector (x, y, z) of the origin of the segment in the global frame in [rad/s].
<acceleration>
	Sample 1 <F v=" Gaseg1 Gaseg2 … Gaseg23 " />
  Sample 2 <F v=" Gaseg1 Gaseg2 … Gaseg23 " />
	…
	Sample n <F v=" Gaseg1 Gaseg2 … Gaseg23 " />
</acceleration>
Gaseg is the 1x3 acceleration vector (x, y, z) of the origin of the segment in the global frame in [m/(s*s)].
Gwaseg is the 1x3 angular acceleration vector (x, y, z) of the origin of the segment in the global frame in [rad/(s*s)].
<ang_acceleration>
	Sample 1 <F v=" Gwaseg1 Gwaseg2 … Gwaseg23 " />
  Sample 2 <F v=" Gwaseg1 Gwaseg2 … Gwaseg23 " />
	…
	Sample n <F v=" Gwaseg1 Gwaseg2 … Gwaseg23 " />
</ang_acceleration>

T-pose

The <tpose> section describes the positions and rotations of all segments during a T‐pose. All kinematic data is expressed in the global coordinate system.

Definition of segment axes

Be careful: The use of the colors in the Moven Software and its documentation is different from use in the Nimue modules. Last is defined the same as in showc4d from Jan Simon.
Axis Nimue (Show4d) and showc4d (MoMo) Moven
x
red

blue
y
green

green
z
blue

red
Segment Label

1 Pelvis

2 L5

3 L3

4 T12

5 T8

6 Neck

7 Head

8 RightShoulder

9 RightUpperArm

10 RightForeArm

11 RightHand

12 LeftShoulder

13 LeftUpperArm

14 LeftForeArm

15 LeftHand

16 RightUpperLeg

17 RightLowerLeg

18 RightFoot

19 RightToe

20 LeftUpperLeg

21 LeftLowerLeg

22 LeftFoot

23 LeftToe

Disadvantages of this file format

It is nice to have an xml export but the definition is not state of the art:

No well formed xml header
No .dtd or schema file is defined.
No namespace is defined.
Boolean attributes are defines by numbers 0 and 1 instead of "true" and "false.
No definition of the used character set even though not only ASCII characters are used
fix number of segments are assumed, no information about the count of segments in the mvnxinfo element

Disadvantages due to missing content:

Only segment data no sensor data is available
No information about incorrect measured data or quality of the data is available

Known bugs:

In most cases the end entity </mvnx> at the end of the document is missed.

Processing flags

Processing flags are used to specify which parts of the .mvnx file should be loaded (if available).

Attribute name	default value	Description
EVENTS	true
POSITION	false	position in local coordinates of a segments coordinate system
ORIGIN	true	position of the orign of a segments coordinate system
ORIENTATION	false	orientation of a segments coordinate system saved as quaternions
VELOCITY	false
ACCELERATION	false
TIMESERIES	true	timeseries (POSITION and/or ORIGIN) should be loaded. This flag is automatically set to true, if one of the flags POSITION or ORIGIN is set to true.
QUATERNIONS	false	If set to false the orientations are defined by column vectors of a 3x3 matrix instead of the original quaternions.

If trial loading is specified by a "labelset" a subset of timeseries can be specified to be loaded. For the label names suffix conventions are defined as follows:

Label suffix name	Description
Position	appended to specify position data with math type 3d-vector
Velocity
Acceleration
Rotation	appended to specify rotation data with math type 3x3-matrix or quaternion
AngularVelocity
AngularAcceleration

Attribute	Default	description
frameCount		count of frames
frameRate		frames per second
recDate		Unknow format, e.g. 1239100243 recorded 2009
originalFilename		absolute path to the original ".mvn" file
velData	0	set to "1" if position velocity data is available
accData	0	set to "1" if position acceleration data is available
angVelData	0	set to "1" if angular velocity data is available
angAccData	0	set to "1" if angular acceleration data is available

marker (event) name	description
RHS	right foot strike
LHS	left foot strike
RTO	right foot off
LTO	left foot off
LG	special meaning in the gaitlab heidelberg: 1. between LHS and LTO to indicate that the kinetics is usable, 2. if there are more then one of this events between LHS and LTO first and last LG event defines start and end of a foot flat phase of the left side
RG	special meaning in the gaitlab heidelberg: 1. between RHS and RTO to indicate that the kinetics is usable, 2. if there are more then one of this events between RHS and RTO first and last RG event defines start and end of a foot flat phase of the right side
GG	general event of no specific side

Axis	Nimue (Show4d) and showc4d (MoMo)	Moven
x	red	blue
y	green	green
z	blue	red

Segment	Label
1	Pelvis
2	L5
3	L3
4	T12
5	T8
6	Neck
7	Head
8	RightShoulder
9	RightUpperArm
10	RightForeArm
11	RightHand
12	LeftShoulder
13	LeftUpperArm
14	LeftForeArm
15	LeftHand
16	RightUpperLeg
17	RightLowerLeg
18	RightFoot
19	RightToe
20	LeftUpperLeg
21	LeftLowerLeg
22	LeftFoot
23	LeftToe