def setUp(self):
self.init_probs = [0.5, 0.5]
self.transition_probs = [
[0.9, 0.1],
[0.1, 0.9],
]
self.emission_probs = [
[0.7, 0.3],
[0.3, 0.7],
]
self.decoder = viterbi.SimpleViterbiDecoder(
init_probs=self.init_probs,
transition_probs=self.transition_probs,
emission_probs=self.emission_probs)
def _compute_flight(self):
"""Adds boolean flag .flying to self.fixes."""
emissions = self._flying_emissions()
decoder = viterbi.SimpleViterbiDecoder(
# More likely to start the log standing, i.e. not in flight
init_probs=[0.80, 0.20],
transition_probs=[
[0.9926, 0.0074], # transitions from standing
[0.0003, 0.9997], # transitions from flying
],
emission_probs=[
[0.974, 0.026], # emissions from standing
[0.031, 0.969], # emissions from flying
])
output = decoder.decode(emissions)
for fix, output in zip(self.fixes, output):
fix.flying = (output == 1)
def _compute_circling(self):
"""Adds .circling to self.fixes."""
emissions = self._circling_emissions()
decoder = viterbi.SimpleViterbiDecoder(
# More likely to start in straight flight than in circling
init_probs=[0.80, 0.20],
transition_probs=[
[0.982, 0.018], # transitions from straight flight
[0.030, 0.970], # transitions from circling
],
emission_probs=[
[0.942, 0.058], # emissions from straight flight
[0.093, 0.907], # emissions from circling
])
output = decoder.decode(emissions)
for i in range(len(self.fixes)):
self.fixes[i].circling = (output[i] == 1)
def _compute_flight(self):
"""Adds boolean flag .flying to self.fixes.
Two pass:
1. Viterbi decoder
2. Only emit landings (0) if the downtime is more than
_config.min_landing_time (or it's the end of the log).
"""
# Step 1: the Viterbi decoder
emissions = self._flying_emissions()
decoder = viterbi.SimpleViterbiDecoder(
# More likely to start the log standing, i.e. not in flight
init_probs=[0.80, 0.20],
transition_probs=[
[0.9995, 0.0005], # transitions from standing
[0.0005, 0.9995], # transitions from flying
],
emission_probs=[
[0.8, 0.2], # emissions from standing
[0.2, 0.8], # emissions from flying
])
outputs = decoder.decode(emissions)
# Step 2: apply _config.min_landing_time.
ignore_next_downtime = False
apply_next_downtime = False
for i, (fix, output) in enumerate(zip(self.fixes, outputs)):
if output == 1:
fix.flying = True
# We're in flying mode, therefore reset all expectations
# about what's happening in the next down mode.
ignore_next_downtime = False
apply_next_downtime = False
else:
if apply_next_downtime or ignore_next_downtime:
if apply_next_downtime:
fix.flying = False
else:
fix.flying = True
else:
# We need to determine whether to apply_next_downtime
# or to ignore_next_downtime. This requires a scan into
# upcoming fixes. Find the next fix on which
# the Viterbi decoder said "flying".
j = i + 1
while j < len(self.fixes):
upcoming_fix_decoded = outputs[j]
if upcoming_fix_decoded == 1:
break
j += 1
if j == len(self.fixes):
# No such fix, end of log. Then apply.
apply_next_downtime = True
fix.flying = False
else:
# Found next flying fix.
upcoming_fix = self.fixes[j]
upcoming_fix_time_ahead = upcoming_fix.rawtime - fix.rawtime
# If it's far enough into the future of then apply.
if upcoming_fix_time_ahead >= self._config.min_landing_time:
apply_next_downtime = True
fix.flying = False
else:
ignore_next_downtime = True
fix.flying = True