Add tool for plotting fft graphs of log entries

tools/fft.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+
+"""Show Fast Fourier Transform plot for log entry.
+
+Usage:
+  fft.py <csv_log_file> <log_entry>
+"""
+
+import docopt
+import csv
+import numpy as np
+import matplotlib.pyplot as plt
+
+args = docopt.docopt(__doc__)
+log_file = args['<csv_log_file>']
+log_entry = args['<log_entry>']
+
+csv_reader = csv.reader(open(log_file, 'r'), delimiter=',')
+header = next(csv_reader)
+log_entry_index = header.index(log_entry)
+
+data = [[float(value) for value in row] for row in csv_reader]
+data = sorted(data, key=lambda row: row[0])
+records = [row[log_entry_index] for row in data]
+duration = data[-1][0] - data[0][0]
+sample_rate = len(data) / duration
+
+print('Duration: ', duration)
+print('Mean sample rate: ', sample_rate)
+print('Mean dt: ', 1 / sample_rate)
+
+N = int(sample_rate * duration)
+
+yf = np.fft.rfft(records)
+xf = np.fft.rfftfreq(N, 1 / sample_rate)
+
+plt.plot(xf, np.abs(yf))
+plt.title('FFT of ' + log_entry)
+plt.xlabel('Frequency')
+plt.ylabel('Amplitude')
+plt.grid(True, which='both', color='#eeeeee')
+plt.minorticks_on()
+plt.get_current_fig_manager().set_window_title(log_entry)
+plt.show()