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#!/usr/bin/env python
"""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.*
Proceedings of the 2000 symposium on Eye tracking research & applications (ETRA'00, 71-78).
[https://doi.org/10.1145/355017.355028](https://doi.org/10.1145/355017.355028)
"""
__author__ = "Théo de la Hogue"
__credits__ = []
__copyright__ = "Copyright 2023, Ecole Nationale de l'Aviation Civile (ENAC)"
__license__ = "BSD"
from typing import TypeVar, Tuple
from dataclasses import dataclass, field
import math
from argaze import GazeFeatures
import numpy
import cv2
GazeMovementType = TypeVar('GazeMovement', bound="GazeMovement")
# Type definition for type annotation convenience
FixationType = TypeVar('Fixation', bound="Fixation")
# Type definition for type annotation convenience
SaccadeType = TypeVar('Saccade', bound="Saccade")
# Type definition for type annotation convenience
@dataclass(frozen=True)
class Fixation(GazeFeatures.Fixation):
"""Define dispersion based fixation."""
deviation_max: float = field(init=False)
"""Maximal gaze position distance to the centroïd."""
def __post_init__(self):
super().__post_init__()
points = self.positions.values()
points_x, points_y = [p[0] for p in points], [p[1] for p in points]
points_array = numpy.column_stack([points_x, points_y])
centroid_array = numpy.array([numpy.mean(points_x), numpy.mean(points_y)])
deviations_array = numpy.sqrt(numpy.sum((points_array - centroid_array)**2, axis=1))
# Update frozen focus attribute using centroid
object.__setattr__(self, 'focus', (centroid_array[0], centroid_array[1]))
# Update frozen deviation_max attribute
object.__setattr__(self, 'deviation_max', max(deviations_array))
def point_deviation(self, gaze_position) -> float:
"""Get distance of a point from the fixation's centroïd."""
return numpy.sqrt((self.focus[0] - gaze_position.value[0])**2 + (self.focus[1] - gaze_position.value[1])**2)
def overlap(self, fixation) -> bool:
"""Does a gaze position from another fixation having a deviation to this fixation centroïd smaller than maximal deviation?"""
points = fixation.positions.values()
points_x, points_y = [p[0] for p in points], [p[1] for p in points]
points_array = numpy.column_stack([points_x, points_y])
centroid_array = numpy.array([self.focus[0], self.focus[1]])
deviations_array = numpy.sqrt(numpy.sum((points_array - centroid_array)**2, axis=1))
return min(deviations_array) <= self.deviation_max
def merge(self, fixation) -> FixationType:
"""Merge another fixation into this fixation."""
self.positions.append(fixation.positions)
self.__post_init__()
return self
def draw(self, frame: numpy.array, color=(127, 127, 127), border_color=(255, 255, 255)):
"""Draw fixation into frame."""
cv2.circle(frame, (int(self.focus[0]), int(self.focus[1])), int(self.deviation_max), color, -1)
cv2.circle(frame, (int(self.focus[0]), int(self.focus[1])), int(self.deviation_max), border_color, len(self.positions))
@dataclass(frozen=True)
class Saccade(GazeFeatures.Saccade):
"""Define dispersion based saccade."""
def __post_init__(self):
super().__post_init__()
def draw(self, frame: numpy.array, color=(255, 255, 255)):
"""Draw saccade into frame."""
_, start_position = self.positions.first
_, last_position = self.positions.last
cv2.line(frame, (int(start_position[0]), int(start_position[1])), (int(last_position[0]), int(last_position[1])), color, 2)
@dataclass
class GazeMovementIdentifier(GazeFeatures.GazeMovementIdentifier):
deviation_max_threshold: int|float
"""Maximal distance allowed to consider a gaze movement as a fixation."""
duration_min_threshold: int|float
"""Minimal duration allowed to consider a gaze movement as a fixation.
It is also used as maximal duration allowed to consider a gaze movement as a saccade."""
def __post_init__(self):
self.__valid_positions = GazeFeatures.TimeStampedGazePositions()
self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
def identify(self, ts, gaze_position, terminate=False) -> GazeMovementType:
"""Identify gaze movement from successive timestamped gaze positions.
The optional *terminate* argument allows to notify identification algorithm that given gaze position will be the last one.
"""
# Ignore non valid gaze position
if not gaze_position.valid:
return None if not terminate else self.current_fixation
# Check if too much time elapsed since last gaze position
if len(self.__valid_positions) > 0:
ts_last, _ = self.__valid_positions.last
if (ts - ts_last) > self.duration_min_threshold:
# Get last movement
last_movement = self.current_saccade if len(self.__fixation_positions) == 0 else self.current_fixation
# Clear all former gaze positions
self.__valid_positions = GazeFeatures.TimeStampedGazePositions()
self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
# Store valid gaze position
self.__valid_positions[ts] = gaze_position
# Return last valid movement if exist
return last_movement
# Store gaze positions until a minimal duration
self.__valid_positions[ts] = gaze_position
first_ts, _ = self.__valid_positions.first
last_ts, _ = self.__valid_positions.last
# Once the minimal duration is reached
if last_ts - first_ts >= self.duration_min_threshold:
# Calculate the deviation of valid gaze positions
deviation = Fixation(self.__valid_positions).deviation_max
# Valid gaze positions deviation small enough
if deviation <= self.deviation_max_threshold:
# Store last saccade
last_saccade = self.current_saccade
# Clear saccade positions
self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
# Copy valid gaze positions into fixation positions
self.__fixation_positions = self.__valid_positions.copy()
# Output last saccade
return last_saccade if not terminate else self.current_fixation
# Valid gaze positions deviation too wide while identifying fixation
elif len(self.__fixation_positions) > 0:
# Store last fixation
last_fixation = self.current_fixation
# Start saccade positions with current gaze position
self.__saccade_positions[ts] = gaze_position
# Clear fixation positions
self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
# Clear valid positions
self.__valid_positions = GazeFeatures.TimeStampedGazePositions()
# Output last fixation
return last_fixation if not terminate else self.current_saccade
# Valid gaze positions deviation too wide while identifying saccade (or not)
else:
# Move oldest valid position into saccade positions
first_ts, first_position = self.__valid_positions.pop_first()
self.__saccade_positions[first_ts] = first_position
@property
def current_fixation(self) -> FixationType:
if len(self.__fixation_positions) > 0:
return Fixation(self.__fixation_positions)
@property
def current_saccade(self) -> SaccadeType:
if len(self.__saccade_positions) > 0:
return Saccade(self.__saccade_positions)
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