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"""Velocity threshold identification (I-VT) module."""
__author__ = "Théo de la Hogue"
__credits__ = []
__copyright__ = "Copyright 2023, Ecole Nationale de l'Aviation Civile (ENAC)"
__license__ = "BSD"
from typing import TypeVar, Tuple
import math
from argaze import GazeFeatures, DataFeatures
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
class Fixation(GazeFeatures.Fixation):
"""Define dispersion based fixation."""
def __init__(self, positions: GazeFeatures.TimeStampedGazePositions = (), finished: bool = False, message: str = None, **kwargs):
super().__init__(positions, finished, message, **kwargs)
if positions:
positions_array = numpy.asarray(self.values())
centroid = numpy.mean(positions_array, axis=0)
deviations_array = numpy.sqrt(numpy.sum((positions_array - centroid)**2, axis=1))
# Set focus as positions centroid
self.focus = (centroid[0], centroid[1])
# Set deviation_max attribute
self.__deviation_max = deviations_array.max()
@property
def deviation_max(self):
"""Get fixation's maximal deviation."""
return self.__deviation_max
def is_overlapping(self, fixation: FixationType) -> bool:
"""Does a gaze position from another fixation having a deviation to this fixation centroïd smaller than maximal deviation?"""
positions_array = numpy.asarray(fixation.values())
centroid = numpy.mean(self.focus, axis=0)
deviations_array = numpy.sqrt(numpy.sum((positions_array - centroid)**2, axis=1))
return min(deviations_array) <= self.deviation_max
def draw(self, image: numpy.array, deviation_circle_color: tuple = None, duration_border_color: tuple = None, duration_factor: float = 1., draw_positions: dict = None):
"""Draw fixation into image.
Parameters:
deviation_circle_color: color of circle representing fixation's deviation
duration_border_color: color of border representing fixation's duration
duration_factor: how many pixels per duration unit
"""
# Draw duration border if required
if duration_border_color is not None:
cv2.circle(image, (int(self.focus[0]), int(self.focus[1])), int(self.deviation_max), duration_border_color, int(self.duration * duration_factor))
# Draw deviation circle if required
if deviation_circle_color is not None:
cv2.circle(image, (int(self.focus[0]), int(self.focus[1])), int(self.deviation_max), deviation_circle_color, -1)
# Draw positions if required
if draw_positions is not None:
self.draw_positions(image, **draw_positions)
class Saccade(GazeFeatures.Saccade):
"""Define dispersion based saccade."""
def __init__(self, positions: GazeFeatures.TimeStampedGazePositions = (), finished: bool = False, message: str = None, **kwargs):
super().__init__(positions, finished, message, **kwargs)
def draw(self, image: numpy.array, line_color: tuple = None):
"""Draw saccade into image.
Parameters:
line_color: color of line from first position to last position
"""
# Draw line if required
if line_color is not None:
start_position = self[0]
last_position = self[-1]
cv2.line(image, (int(start_position[0]), int(start_position[1])), (int(last_position[0]), int(last_position[1])), line_color, 2)
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)
Parameters:
velocity_max_threshold: Maximal velocity allowed to consider a gaze movement as a fixation.
duration_min_threshold: Minimal duration allowed to wait valid gaze positions.
"""
def __init__(self, velocity_max_threshold: int|float, duration_min_threshold: int|float):
super().__init__()
self.__velocity_max_threshold = velocity_max_threshold
self.__duration_min_threshold = duration_min_threshold
self.__last_ts = -1
self.__last_position = None
self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
@property
def velocity_max_threshold(self):
"""Get identifier's velocity max threshold."""
return self.__velocity_max_threshold
@property
def duration_min_threshold(self):
"""Get identifier duration min threshold."""
return self.__duration_min_threshold
@DataFeatures.PipelineStepMethod
def identify(self, gaze_position, terminate=False) -> GazeMovementType:
# Ignore empty gaze position
if not gaze_position:
return GazeFeatures.GazeMovement() if not terminate else self.current_fixation().finish()
# Store first valid position
if self.__last_ts < 0:
self.__last_ts = gaze_position.timestamp
self.__last_position = gaze_position
return GazeFeatures.GazeMovement()
# Check if too much time elapsed since last gaze position
if (gaze_position.timestamp - self.__last_ts) > self.duration_min_threshold:
# Remember last position
self.__last_ts = gaze_position.timestamp
self.__last_position = gaze_position
# Get last movement
last_movement = self.current_gaze_movement().finish()
# 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) / (gaze_position.timestamp - self.__last_ts))
# Remember last position
self.__last_ts = gaze_position.timestamp
self.__last_position = gaze_position
# Velocity is greater than threshold
if velocity > self.velocity_max_threshold:
last_fixation = GazeFeatures.GazeMovement()
# Does last fixation exist?
if len(self.__fixation_positions) > 0:
# Copy most recent fixation position into saccade positions
self.__saccade_positions.append(self.__fixation_positions[-1])
# Create last fixation
last_fixation = self.current_fixation().finish()
# Clear fixation positions
self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
# Append to saccade positions
self.__saccade_positions.append(gaze_position)
# Output last fixation
return last_fixation if not terminate else self.current_saccade().finish()
# Velocity is less or equals to threshold
else:
last_saccade = GazeFeatures.GazeMovement()
# Does last saccade exist?
if self.__saccade_positions:
# Copy most recent saccade position into fixation positions
self.__fixation_positions.append(self.__saccade_positions[-1])
# Create last saccade
last_saccade = self.current_saccade().finish()
# Clear fixation positions
self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
# Append to fixation positions
self.__fixation_positions.append(gaze_position)
# Output last saccade
return last_saccade if not terminate else self.current_fixation().finish()
# Always return empty gaze movement at least
return GazeFeatures.GazeMovement()
def current_gaze_movement(self) -> GazeMovementType:
# It shouldn't have a current fixation and a current saccade at the same time
assert(not (self.__fixation_positions and self.__saccade_positions))
if self.__fixation_positions:
return Fixation(self.__fixation_positions)
if len(self.__saccade_positions) > 1:
return Saccade(self.__saccade_positions)
# Always return empty gaze movement at least
return GazeFeatures.GazeMovement()
def current_fixation(self) -> FixationType:
if self.__fixation_positions:
return Fixation(self.__fixation_positions)
# Always return empty gaze movement at least
return GazeFeatures.GazeMovement()
def current_saccade(self) -> SaccadeType:
if len(self.__saccade_positions) > 1:
return Saccade(self.__saccade_positions)
# Always return empty gaze movement at least
return GazeFeatures.GazeMovement()
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