to_compamp()

trappist1_6_April_2017_analysis.py

packet_header_size = 64
packet_data_size = 4096
packet_size = packet_header_size + packet_data_size

def to_compamp(segment):  # convert measurement data to timestamp & numpy array
    segment_name = segment[0]
    segment_data = segment[1]
    bytes_per_segment = len(segment_data)
    
    # example:  0:u:e5sdfb0c-3012-49f4-fe9d-12341ecacc91-000001
    segment_nr = int(segment_name.split('-')[-1])
    segment_byte_start = (segment_nr - 1) * bytes_per_segment
    # the number of full packets preceding this segment
    full_packets = int(np.floor(segment_byte_start / packet_size))
    
    remainder = segment_byte_start - (full_packets * packet_size)
    # position where first full packet starts in segment
    start_pos = packet_size - remainder
    
    if remainder == 0:
        start_pos = 0
    # amount of full packets in segment
    packets = (bytes_per_segment - start_pos) // packet_size  
    
    raw = segment_data[start_pos:(start_pos + packets*packet_size)]
    timestamp = unpack('BBBBIBBBBIIIddffQII',
                       segment_data[start_pos:start_pos+packet_header_size])[16]
    
    arr = np.frombuffer(raw, dtype=np.int8)
    arr = arr.reshape((packets, packet_size))[:, packet_header_size:]
             .reshape((packets * packet_data_size))
    n = len(arr) / 2
    
    coef = np.empty(n, complex)
    coef.real = arr[::2].reshape(n)
    coef.imag = arr[1::2].reshape(n)
    
    return timestamp, coef