Get body tracking results

Article
06/26/2019

Body Tracking SDK uses a body tracker object to process Azure Kinect DK captures and generates body tracking results. It also maintains global status of the tracker, processing queues and the output queue. There are three steps in using the body tracker:

Create a tracker
Capture depth and IR images using Azure Kinect DK
Enqueue the capture and pop the results.

Create a tracker

The first step in using body tracking is to create a tracker and requires passing in the sensor calibration k4a_calibration_t structure. The sensor calibration can be queried using the Azure Kinect Sensor SDK k4a_device_get_calibration() function.

k4a_calibration_t sensor_calibration;
if (K4A_RESULT_SUCCEEDED != k4a_device_get_calibration(device, device_config.depth_mode, K4A_COLOR_RESOLUTION_OFF, &sensor_calibration))
{
    printf("Get depth camera calibration failed!\n");
    return 0;
}

k4abt_tracker_t tracker = NULL;
k4abt_tracker_configuration_t tracker_config = K4ABT_TRACKER_CONFIG_DEFAULT;
if (K4A_RESULT_SUCCEEDED != k4abt_tracker_create(&sensor_calibration, tracker_config, &tracker))
{
    printf("Body tracker initialization failed!\n");
    return 0;
}

Capture depth and IR images

Image capture using Azure Kinect DK is covered in the retrieve images page.

Note

K4A_DEPTH_MODE_NFOV_UNBINNED or K4A_DEPTH_MODE_WFOV_2X2BINNED modes are recommended for best performance and accuracy. Do not use the K4A_DEPTH_MODE_OFF or K4A_DEPTH_MODE_PASSIVE_IR modes.

The supported Azure Kinect DK modes are described in the Azure Kinect DK hardware specification and k4a_depth_mode_t enumerations.

// Capture a depth frame
switch (k4a_device_get_capture(device, &capture, TIMEOUT_IN_MS))
{
case K4A_WAIT_RESULT_SUCCEEDED:
    break;
case K4A_WAIT_RESULT_TIMEOUT:
    printf("Timed out waiting for a capture\n");
    continue;
    break;
case K4A_WAIT_RESULT_FAILED:
    printf("Failed to read a capture\n");
    goto Exit;
}

Enqueue the capture and pop the results

The tracker internally maintains an input queue and an output queue to asynchronously process the Azure Kinect DK captures more efficiently. Use the k4abt_tracker_enqueue_capture() function to add a new capture to the input queue. Use the k4abt_tracker_pop_result() function to pop a result from the output queue. Use of the timeout value is dependent on the application and controls the queuing wait time.

No Wait processing

Use this pattern for single-threaded applications that need immediate results and can accommodate dropped frames (e.g. viewing live video from a device). The simple_3d_viewer sample located in GitHub Azure-Kinect-Samples is an example of no wait processing.

k4a_wait_result_t queue_capture_result = k4abt_tracker_enqueue_capture(tracker, sensor_capture, 0);
k4a_capture_release(sensor_capture); // Remember to release the sensor capture once you finish using it
if (queue_capture_result == K4A_WAIT_RESULT_FAILED)
{
    printf("Error! Adding capture to tracker process queue failed!\n");
    break;
}

k4abt_frame_t body_frame = NULL;
k4a_wait_result_t pop_frame_result = k4abt_tracker_pop_result(tracker, &body_frame, 0);
if (pop_frame_result == K4A_WAIT_RESULT_SUCCEEDED)
{
    // Successfully popped the body tracking result. Start your processing
    ...

    k4abt_frame_release(body_frame); // Remember to release the body frame once you finish using it
}

Wait processing

Use this pattern for applications that do not need results for every frames (e.g. processing a video from a file). The simple_sample.exe sample located in GitHub Azure-Kinect-Samples is an example of wait processing.

k4a_wait_result_t queue_capture_result = k4abt_tracker_enqueue_capture(tracker, sensor_capture, K4A_WAIT_INFINITE);
k4a_capture_release(sensor_capture); // Remember to release the sensor capture once you finish using it
if (queue_capture_result != K4A_WAIT_RESULT_SUCCEEDED)
{
    // It should never hit timeout or error when K4A_WAIT_INFINITE is set.
    printf("Error! Adding capture to tracker process queue failed!\n");
    break;
}

k4abt_frame_t body_frame = NULL;
k4a_wait_result_t pop_frame_result = k4abt_tracker_pop_result(tracker, &body_frame, K4A_WAIT_INFINITE);
if (pop_frame_result != K4A_WAIT_RESULT_SUCCEEDED)
{
    // It should never hit timeout or error when K4A_WAIT_INFINITE is set.
    printf("Error! Popping body tracking result failed!\n");
    break;
}
// Successfully popped the body tracking result. Start your processing
...

k4abt_frame_release(body_frame); // Remember to release the body frame once you finish using it

Next steps

Access data in body frame

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