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Motion Capture Data Export Format

  • Updated

Some active tasks capture detailed motion data. For example, the fitness check, short walk, and range of motion tasks can record details about the device motion and acceleration during the test.

Table of Contents

Data File Organization

Motion capture data is stored separately from other exported data. There are separate motion capture files for each survey step that recorded motion data. These files are stored within the "SurveyData" folder using the following path:

SurveyData/{ParticipantIdentifier}/{SurveyResultKey}/{StepIdentifier}/{DataFile}

For example:

SurveyData/264b2a09-3ff0-4668-8a0a-bd0ee59bf9584/24be41e0-a2e2-40ce-871e-9ffa7e685926/GAIT_TEST/Accelerometer.json

The ParticipantIdentifier, SurveyResultKey, and StepIdentifier all correspond to the values in the Survey Step Results export file.

Data file names are shown in the table below:

Data File Name
Accelerometer Data Accelerometer.json
Pedometer Data Pedometer.json
Device Motion Data DeviceMotion.json
If you do not see the detailed motion data files for a survey, contact us to see if it is available for the active task you're using.

Accelerometer Data

Accelerometer data captures device motion at a set frequency (100Hz by default). 

Field Description
x, y, z The acceleration, in g-force (G's), recorded along the x-, y-, and z-axes.
timestamp

A device timestamp marking the time the reading was recorded.

 
{
  "items": [
    {
      "y": -0.440582275390625,
      "timestamp": 867.9697944999999,
      "z": -0.888946533203125,
      "x": 0.0896148681640625
    },
    {
      "y": -0.4400634765625,
      "timestamp": 867.9797424999999,
      "z": -0.8815765380859374,
      "x": 0.0867767333984375
    },
    ...
}

Pedometer Data

Pedometer data captures a summary of the participant's movement, as reported by the device.

Field Description

floorsAscended
floorsDescended

 Number of floors ascended or descended.
startDate
endDate 		The start and end date of the time period represented by the data capture.
numberOfSteps The number of steps taken.
distance
 		The distance traveled, in meters. 
{
  "items": [
    {
      "floorsAscended": 0,
      "floorsDescended": 0,
      "endDate": "2021-01-20T11:12:39-0600",
      "startDate": "2021-01-20T11:12:32-0600",
      "numberOfSteps": 9,
      "distance": 3.9248944195569493
    },
    {
      "floorsAscended": 0,
      "floorsDescended": 0,
      "endDate": "2021-01-20T11:12:42-0600",
      "startDate": "2021-01-20T11:12:32-0600",
      "numberOfSteps": 13,
      "distance": 5.865757531253621
    },
    ...
  ]}

Device Motion Data

This data file captures general device orientation and motion at a set frequency (100Hz by default). 

Field Description
attitude

Device attitude, recorded as a quaternion (q) representing a rotation of theta radians about the unit vector {x,y,z}.

{q.x, q.y, q.z, q.w} satisfies the following:

q.x = x * sin(theta / 2)
q.y = y * sin(theta / 2)
q.z = z * sin(theta / 2)
q.w = cos(theta / 2)
timestamp A device timestamp marking the time the reading was recorded.
rotationRate Device rotation acceleration, in g-force (G's), recorded along the x-, y-, and z-axes.
userAcceleration Device user acceleration, in g-force (G's), recorded along the x-, y-, and z-axes.
gravity
 		Acceleration of gravity, in g-force (G's), recorded along the x-, y-, and z-axes.
magneticField

Measure of magnetic field, in microteslas, for the x-, y-, and z-axes. The accuracy field reflects the accuracy of the measurement:

  • -1 = Uncalibrated
  • 0 = Low
  • 1 = Medium
  • 2 = High
 
{
  "items": [
    {
      "attitude": {
        "y": 0.04419703935756934,
        "w": 0.9729538185300793,
        "z": 0,
        "x": 0.22673223719225216
      },
      "timestamp": 867.9772564999998,
      "rotationRate": {
        "x": -0.04906965792179108,
        "y": 0.005430211313068866,
        "z": 0.0395255722105503
      },
      "userAcceleration": {
        "x": 0.002985894680023193,
        "y": 0.0006634891033172609,
        "z": 0.006300091743469239
      },
      "gravity": {
        "x": 0.08600335568189622,
        "y": -0.4411999881267547,
        "z": -0.8932782411575315
      },
      "magneticField": {
        "y": 0,
        "z": 0,
        "x": 0,
        "accuracy": -1
      }
    },
    {
      "attitude": {
        "y": 0.04417244199634487,
        "w": 0.9730006423304092,
        ...
    },
    ...
  ]}

 

 

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