Merge pull request #490 from roboflow/feature/update_line_zone

Add documentation and improvements to "LineZone" functionality

docs/detection/tools/line_zone.md

@@ -0,0 +1,3 @@
+## LineZone
+
+:::supervision.detection.line_counter.LineZone

mkdocs.yml

@@ -39,6 +39,7 @@ nav:
         - Core: detection/core.md
         - Utils: detection/utils.md
     - Tools:
+        - Line Zone: detection/tools/line_zone.md
         - Polygon Zone: detection/tools/polygon_zone.md
         - Inference Slicer: detection/tools/inference_slicer.md
     - Annotators: annotators.md

supervision/detection/line_counter.py

@@ -1,4 +1,4 @@
-from typing import Dict, Optional
+from typing import Dict, Optional, Tuple
 
 import cv2
 import numpy as np
@@ -10,42 +10,54 @@ from supervision.geometry.core import Point, Rect, Vector
 
 class LineZone:
     """
-    Count the number of objects that cross a line.
+    This class is responsible for counting the number of objects that cross a
+    predefined line.
+
+    !!! warning
+
+        LineZone utilizes the `tracker_id`. Read
+        [here](https://supervision.roboflow.com/trackers/) to learn how to plug
+        tracking into your inference pipeline.
+
+    Attributes:
+        in_count (int): The number of objects that have crossed the line from outside
+            to inside.
+        out_count (int): The number of objects that have crossed the line from inside
+            to outside.
     """
 
     def __init__(self, start: Point, end: Point):
         """
-        Initialize a LineCounter object.
-
-        Attributes:
+        Args:
             start (Point): The starting point of the line.
             end (Point): The ending point of the line.
-
         """
         self.vector = Vector(start=start, end=end)
         self.tracker_state: Dict[str, bool] = {}
         self.in_count: int = 0
         self.out_count: int = 0
 
-    def trigger(self, detections: Detections) -> np.ndarray:
+    def trigger(self, detections: Detections) -> Tuple[np.ndarray, np.ndarray]:
         """
-        Update the in_count and out_count for the detections that cross the line.
+        Update the `in_count` and `out_count` based on the objects that cross the line.
 
-        Attributes:
-            detections (Detections): The detections for which to update the counts.
+        Args:
+            detections (Detections): A list of detections for which to update the
+                counts.
 
         Returns:
-            np.ndarray: A boolean array indicating
-            which detection has crossed the line on the either sides
+            A tuple of two boolean NumPy arrays. The first array indicates which
+                detections have crossed the line from outside to inside. The second
+                array indicates which detections have crossed the line from inside to
+                outside.
         """
-        crossed = np.full(len(detections), False)
+        crossed_in = np.full(len(detections), False)
+        crossed_out = np.full(len(detections), False)
 
         for i, (xyxy, _, confidence, class_id, tracker_id) in enumerate(detections):
-            # handle detections with no tracker_id
             if tracker_id is None:
                 continue
 
-            # we check if all four anchors of bbox are on the same side of vector
             x1, y1, x2, y2 = xyxy
             anchors = [
                 Point(x=x1, y=y1),
@@ -55,30 +67,27 @@ class LineZone:
             ]
             triggers = [self.vector.is_in(point=anchor) for anchor in anchors]
 
-            # detection is partially in and partially out
             if len(set(triggers)) == 2:
                 continue
 
             tracker_state = triggers[0]
-            # handle new detection
+
             if tracker_id not in self.tracker_state:
                 self.tracker_state[tracker_id] = tracker_state
                 continue
 
-            # handle detection on the same side of the line
             if self.tracker_state.get(tracker_id) == tracker_state:
                 continue
 
             self.tracker_state[tracker_id] = tracker_state
             if tracker_state:
                 self.in_count += 1
-                crossed[i] = True
-
+                crossed_in[i] = True
             else:
                 self.out_count += 1
-                crossed[i] = True
+                crossed_out[i] = True
 
-        return crossed
+        return crossed_in, crossed_out
 
 
 class LineZoneAnnotator: