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Viewing Events

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Events occur during an acquisition at a particular time when a condition is met. These events include:

  • Error

  • FramesAcquired

  • Start

  • Stop

  • Timer

  • Trigger

All acquisitions consist of at least 3 events:

  • Starting the device

  • Triggering the device

  • Stopping the device.

Executing an Acquisition

Initiate a basic acquisition using a video input object.

% Access an image acquisition device.
vidobj = videoinput('winvideo', 1);

% Use a manual trigger to initiate data logging.
triggerconfig(vidobj, 'manual');

% Start the acquisition.
start(vidobj)

% Trigger the object to start logging and allow the acquisition to run for
% couple of seconds.
trigger(vidobj)
pause(2);

% Stop the acquisition
stop(vidobj)

Viewing Event Information

To view event information for the acquisition, access the EventLog property of the video input object. Events are recorded in chronological order. 

% View the event log.
events = vidobj.EventLog

events = 

1x3 struct array with fields:
    Type
    Data

Each event provides information on the state of the object at the time the event occurred.

% Display first event.
event1 = events(1)

event1 = 

    Type: 'Start'
    Data: [1x1 struct]


data1 = events(1).Data

data1 = 

             AbsTime: [2005 6 5 23 53 14.1680]
    FrameMemoryLimit: 341692416
     FrameMemoryUsed: 0
         FrameNumber: 0
       RelativeFrame: 0
        TriggerIndex: 0


% Display second event.
event2 = events(2)

event2 = 

    Type: 'Trigger'
    Data: [1x1 struct]


data2 = events(2).Data

data2 = 

             AbsTime: [2005 6 5 23 53 14.7630]
    FrameMemoryLimit: 341692416
     FrameMemoryUsed: 0
         FrameNumber: 0
       RelativeFrame: 0
        TriggerIndex: 1


% Display third event.
event3 = events(3)

event3 = 

    Type: 'Stop'
    Data: [1x1 struct]


data3 = events(3).Data

data3 = 

             AbsTime: [2005 6 5 23 53 16.9970]
    FrameMemoryLimit: 341692416
     FrameMemoryUsed: 768000
         FrameNumber: 5
       RelativeFrame: 5
        TriggerIndex: 1


% Once the video input object is no longer needed, delete
% it and clear it from the workspace.
delete(vidobj)
clear vidobj