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Use Logged Sensor Data

This example shows how to plot orientation data. You can use the logged sensor data either during or after acquisition for plotting and other analyses.

This example assumes that you have already installed and set up MATLAB® Mobile™ on your iOS device and connected it to your computer running MATLAB or to the MathWorks Cloud. For information about these steps, see Get Started with iOS Sensors.

  1. Start MATLAB Mobile on your iOS device.

  2. On the Sensors screen, tap the Orientation sensor.

  3. Place the device where you want it for sending the sensor data.

  4. On your computer, in MATLAB, connect to the device.

    connector on

    Alternatively, if you are running MATLAB using MathWorks Cloud, log in to the Cloud.

  5. In MATLAB, create a mobiledev object, m.

    m = mobiledev
    mobiledev with properties:
    
                       Connected: 1
                         Logging: 0
                InitialTimestamp: ''
    
       AccelerationSensorEnabled: 0
    AngularVelocitySensorEnabled: 0
      MagneticFieldSensorEnabled: 0
        OrientationSensorEnabled: 1
           PositionSensorEnabled: 0
                                                                    
    Supported functions

    In the display that is shown when you create the object, a value of 1 means enabled or on, and 0 means not enabled or off. In this example, you can see that the device and computer are connected, and data is not being logged yet. The Orientation sensor is shown as enabled since you selected it on the device.

  6. Begin logging data from the selected sensor by enabling the Logging property.

    m.Logging = 1

    This action starts the transmitting of data from all selected sensors. You can also start transmission by tapping the Start button in MATLAB Mobile.

  7. You can see a display of the object properties any time, using the disp function. Now that you have started logging data, the display shows more information.

    disp(m)
    mobiledev with properties:
    
                       Connected: 1
                         Logging: 1
                InitialTimestamp: '06-08-2014 13:45:56.529'
    
       AccelerationSensorEnabled: 0
    AngularVelocitySensorEnabled: 0
      MagneticFieldSensorEnabled: 0
        OrientationSensorEnabled: 1
           PositionSensorEnabled: 0
    
    Current Sensor Values:
                    Acceleration: [0x3 double]  (m/s^2)
                 AngularVelocity: [0x3 double]  (rad/s)
                   MagneticField: [0x3 double]  (microtesla)
                     Orientation: [1.8102 0.0101 -0.0418]  (degrees)
    
           Position Data: 
                        Latitude: [0x1 double]  (degrees)
                       Longitude: [0x1 double]  (degrees)
                           Speed: [0x1 double]  (m/s)
                          Course: [0x1 double]  (degrees)
                        Altitude: [0x1 double]  (m)
              HorizontalAccuracy: [0x1 double]  (m)
                                                                     
    Supported functions

    In the display, you can see that the device and computer are connected, and data is being logged. The InitialTimestamp value shows the timestamp when the first packet of data was logged. The sensor values are displayed, indicating the current measurement value.

  8. After you have collected the amount of data you need, stop logging sensor data.

    m.Logging = 0
  9. You can see the entire log of all readings using the log functions. You can use these functions while you are still logging or after you stop. Each sensor type has a log function:

    accellog — Logged acceleration data

    angvellog — Logged angular velocity data

    magfieldlog — Logged magnetic field data

    orientlog — Logged orientation data

    poslog — Logged position data, including data points for latitude, longitude, speed, course, altitude, and horizontal accuracy.

    See Device Orientation for a diagram showing the X, Y, and Z axes relative to the device.

    To get the logged orientation data from object m, assign the variable o for the logged orientation data and t for the timestamps.

    [o, t] = orientlog(m);

    You can then plot the data.

    plot(t, o) 

    In this example, the Orientation data is from the device being moved a short distance for a few minutes. The plot shows the time (t) against orientation (o).

  10. You can keep the logs to access the data again, or discard them from your MATLAB session:

    discardlogs(m)
  11. When you are done with the session, delete the object.

    clear m
  12. Close the connection between MATLAB and the iOS device.

    connector off