Infrared Tracking
=================

During the loop execution of this example :ref:`code <codetracking>`, the
infrared sensor tracks the LEGO® beacon as it's moved from really close to the
sensor to about 50 centimeters away. Then the beacon is moved from side to side,
for about 50 centimeters as well.

.. image:: ../../images/Infrared-Example.png

.. note::
    Make sure the beacon is *ON* and on channel *1*, and placed in front of the
    sensor before you run the example.

.. _codetracking:

.. code-block:: python

    """ tracking.py 

    Use the infrared sensor to track the LEGO beacon.

    Setup:
        Connect infrared sensor to port number 1.

    """
    # Importing modules and classes
    import time
    import numpy as np
    from pyev3.utils import plot_line
    from pyev3.brick import LegoEV3
    from pyev3.devices import Infrared

    # Defining parameters
    tstop = 20 # Execution loop duration (s)
    tsample = 0.02 # Data sampling period (s)
    tdisp = 0.2 # Screen display period (s)

    # Pre-allocating output arrays
    t = []
    azymuth = []
    proximity = []

    # Creating LEGO EV3 objects
    ev3 = LegoEV3()
    ired = Infrared(ev3, portnum=1, inputmode='seeker')

    # Initializing current time stamp and starting clock
    tprev = 0
    tcurr = 0
    tstart = time.perf_counter()
    # Changing EV3 status light
    ev3.set_statuslight(mode='pulsing')
    # Running execution loop
    print('Running for', tstop, 'seconds ...')
    while tcurr <= tstop:
        # Getting current azymuth and proximity
        (azymcurr, proxcurr) = ired.output
        # Updating previous time and getting current time (s)
        tprev = tcurr
        tcurr = time.perf_counter() - tstart
        # Displaying azymuth and proximity every `tdisp` seconds
        if (np.floor(tcurr/tdisp) - np.floor(tprev/tdisp)) == 1:
            print('Azymuth =', azymcurr, ', Proximity =', proxcurr)
        # Acquiring data every `tsample` seconds
        # and appending values to output arrays
        if (np.floor(tcurr/tsample) - np.floor(tprev/tsample)) == 1:
            t.append(tcurr)
            azymuth.append(azymcurr)
            proximity.append(proxcurr)
    print('Done.')
    # Closing brick connection
    ev3.set_statuslight(mode='solid')
    ev3.close()

    # Plotting results
    plot_line([t]*2, [azymuth, proximity],
              yname=['Azymuth ( - )', 'Proximity ( - )'], axes='multi')