Adding new identification algorithm.

2 files changed, 181 insertions, 1 deletions

diff --git a/src/argaze/GazeAnalysis/VelocityThresholdIdentification.py b/src/argaze/GazeAnalysis/VelocityThresholdIdentification.py
new file mode 100644
index 0000000..5e6ab26
--- /dev/null
+++ b/src/argaze/GazeAnalysis/VelocityThresholdIdentification.py
@@ -0,0 +1,180 @@
+#!/usr/bin/env python
+
+from typing import TypeVar, Tuple
+from dataclasses import dataclass, field
+import math
+
+from argaze import GazeFeatures
+
+import numpy
+
+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
+
+@dataclass(frozen=True)
+class Saccade(GazeFeatures.Saccade):
+    """Define dispersion based saccade."""
+
+    def __post_init__(self):
+        super().__post_init__()
+
+@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. [DOI=http://dx.doi.org/10.1145/355017.355028](DOI=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):
+        """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:
+
+            # Clear all former gaze positions
+            self.__last_ts = ts
+            self.__last_position = gaze_position
+
+            self.__fixation_positions = GazeFeatures.TimeStampedGazePositions()
+            self.__saccade_positions = GazeFeatures.TimeStampedGazePositions()
+
+            return
+        
+        # Velocity
+        velocity = 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 if not terminate else 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 if not terminate else 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)
diff --git a/src/argaze/GazeAnalysis/__init__.py b/src/argaze/GazeAnalysis/__init__.py
index 287425f..7603693 100644
--- a/src/argaze/GazeAnalysis/__init__.py
+++ b/src/argaze/GazeAnalysis/__init__.py
@@ -2,4 +2,4 @@
 .. include:: README.md
 """
 __docformat__ = "restructuredtext"
-__all__ = ['DispersionThresholdIdentification', 'TransitionProbabilityMatrix']
\ No newline at end of file
+__all__ = ['DispersionThresholdIdentification', 'VelocityThresholdIdentification', 'TransitionProbabilityMatrix']
\ No newline at end of file