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#!/usr/bin/env python
import math
from argaze import DataStructures
import numpy
FIXATION_MAX_DURATION = 1000
class GazePosition(DataStructures.DictObject):
"""Define gaze position"""
def __init__(self, x, y):
super().__init__(type(self).__name__, **{'x': x, 'y': y})
class TimeStampedGazePositions(DataStructures.TimeStampedBuffer):
"""Define timestamped buffer to store gaze positions"""
def __setitem__(self, key, value: GazePosition):
"""Force value to be a GazePosition"""
if type(value) != GazePosition:
raise ValueError('value must be a GazePosition')
super().__setitem__(key, value)
class Fixation(DataStructures.DictObject):
"""Define fixation"""
def __init__(self, duration, dispersion, cx, cy):
super().__init__(type(self).__name__, **{'duration': duration, 'dispersion': dispersion, 'centroid': [cx, cy]})
class TimeStampedFixations(DataStructures.TimeStampedBuffer):
"""Define timestamped buffer to store fixations"""
def __setitem__(self, key, value: Fixation):
"""Force value to be a Fixation"""
if type(value) != Fixation:
raise ValueError('value must be a Fixation')
super().__setitem__(key, value)
class FixationIdentifier():
"""Abstract class to define what should provide a fixation identifier"""
fixations = TimeStampedFixations()
saccades = DataStructures.TimeStampedBuffer()
def identify(self, ts_gaze_positions):
raise NotImplementedError('identify() method not implemented')
def __init__(self, ts_gaze_positions: TimeStampedGazePositions):
if type(ts_gaze_positions) != TimeStampedGazePositions:
raise ValueError('argument must be a TimeStampedGazePositions')
# do identification on a copy
self.identify(ts_gaze_positions.copy())
class DispersionBasedFixationIdentifier(FixationIdentifier):
"""Implementation of the I-DT algorithm as described in:
Dario D. Salvucci and Joseph H. Goldberg. 2000. Identifying fixations and
saccades in eye-tracking protocols. In Proceedings of the 2000 symposium
on Eye tracking research & applications (ETRA '00). ACM, New York, NY, USA,
71-78. DOI=http://dx.doi.org/10.1145/355017.355028
"""
def __init__(self, ts_gaze_positions, dispersion_threshold = 10, duration_threshold = 100):
self.__dispersion_threshold = dispersion_threshold
self.__duration_threshold = duration_threshold
super().__init__(ts_gaze_positions)
# euclidian dispersion
def __getEuclideanDispersion(self, ts_gaze_positions_list):
x_list = [gp.x for (ts, gp) in ts_gaze_positions_list]
y_list = [gp.y for (ts, gp) in ts_gaze_positions_list]
cx = numpy.mean(x_list)
cy = numpy.mean(y_list)
c = [cx, cy]
points = numpy.column_stack([x_list, y_list])
dist = (points - c)**2
dist = numpy.sum(dist, axis=1)
dist = numpy.sqrt(dist)
return max(dist), cx, cy
# basic dispersion
def __getDispersion(self, ts_gaze_positions_list):
x_list = [gp.x for (ts, gp) in ts_gaze_positions_list]
y_list = [gp.y for (ts, gp) in ts_gaze_positions_list]
return (max(x_list) - min(x_list)) + (max(y_list) - min(y_list))
def identify(self, ts_gaze_positions):
# while there are 2 gaze positions at least
while len(ts_gaze_positions) >= 2:
# copy remaining timestamped gaze positions
remaining_ts_gaze_positions = ts_gaze_positions.copy()
# select timestamped gaze position until a duration threshold
(ts_start, gaze_position_start) = remaining_ts_gaze_positions.pop_first()
(ts_current, gaze_position_current) = remaining_ts_gaze_positions.pop_first()
ts_gaze_positions_list = [(ts_start, gaze_position_start)]
while (ts_current - ts_start) < self.__duration_threshold:
ts_gaze_positions_list.append( (ts_current, gaze_position_current) )
if len(remaining_ts_gaze_positions) > 0:
(ts_current, gaze_position_current) = remaining_ts_gaze_positions.pop_first()
else:
break
# how much gaze is dispersed ?
dispersion, cx, cy = self.__getEuclideanDispersion(ts_gaze_positions_list)
# little dispersion
if dispersion <= self.__dispersion_threshold:
# remove selected gaze positions
for gp in ts_gaze_positions_list:
ts_gaze_positions.pop_first()
# are next gaze positions not too dispersed ?
while len(remaining_ts_gaze_positions) > 0:
# select next gaze position
ts_gaze_positions_list.append(remaining_ts_gaze_positions.pop_first())
new_dispersion, new_cx, new_cy = self.__getEuclideanDispersion(ts_gaze_positions_list)
# dispersion too wide
if new_dispersion > self.__dispersion_threshold:
# remove last gaze position
ts_gaze_positions_list.pop(-1)
break
# store new dispersion data
dispersion = new_dispersion
cx = new_cx
cy = new_cy
# remove selected gaze position
ts_gaze_positions.pop_first()
# we have a new fixation
ts_list = [ts for (ts, gp) in ts_gaze_positions_list]
duration = ts_list[-1] - ts_list[0]
if duration > FIXATION_MAX_DURATION:
duration = FIXATION_MAX_DURATION
if duration > 0:
# append fixation to timestamped buffer
self.fixations[ts_list[0]] = Fixation(duration, dispersion, cx, cy)
# dispersion too wide : consider next gaze position
else:
ts_gaze_positions.pop_first()
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