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#!/usr/bin/env python
"""Implementation of the I-VT 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, 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.centroid[0] - gaze_position.value[0])**2 + (self.centroid[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.centroid[0], self.centroid[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, image: numpy.array, color=(127, 127, 127), border_color=(255, 255, 255)):
"""Draw fixation into image."""
cv2.circle(image, (int(self.focus[0]), int(self.focus[1])), int(self.deviation_max), color, -1)
cv2.circle(image, (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, image: numpy.array, color=(255, 255, 255)):
"""Draw saccade into image."""
_, start_position = self.positions.first
_, last_position = self.positions.last
cv2.line(image, (int(start_position[0]), int(start_position[1])), (int(last_position[0]), int(last_position[1])), color, 2)
@dataclass
class GazeMovementIdentifier(GazeFeatures.GazeMovementIdentifier):
"""Implementation of the I-VT 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. [http://dx.doi.org/10.1145/355017.355028](http://dx.doi.org/10.1145/355017.355028)
"""
velocity_max_threshold: int|float
"""Maximal velocity 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.__last_ts = -1
self.__last_position = None
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
# Store first valid position
if self.__last_ts < 0:
self.__last_ts = ts
self.__last_position = gaze_position
return
# Check if too much time elapsed since last gaze position
if (ts - self.__last_ts) > self.duration_min_threshold:
# Remember last position
self.__last_ts = ts
self.__last_position = gaze_position
# Get last movement
last_movement = self.current_saccade if len(self.__fixation_positions) == 0 else self.current_fixation
# Clear all former gaze positions
self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
# Return last valid movement if exist
return last_movement
# Velocity
velocity = abs(gaze_position.distance(self.__last_position) / (ts - self.__last_ts))
# Remember last position
self.__last_ts = ts
self.__last_position = gaze_position
# Velocity is greater than threshold
if velocity > self.velocity_max_threshold:
# Append to saccade positions
self.__saccade_positions[ts] = gaze_position
# Does last fixation exist?
if len(self.__fixation_positions) > 0:
last_fixation = Fixation(self.__fixation_positions)
# Clear fixation positions
self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
# Output last fixation
return last_fixation
# Identification must stop: ends with current saccade
if terminate:
return self.current_saccade
# Velocity is less or equals to threshold
else:
# Append to fixation positions
self.__fixation_positions[ts] = gaze_position
# Does last saccade exist?
if len(self.__saccade_positions) > 0:
last_saccade = Saccade(self.__saccade_positions)
# Clear fixation positions
self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
# Output last saccade
return last_saccade
# Identification must stop: ends with current fixation
if terminate:
return self.current_fixation
@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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