ADD: Added a spline annotator

supervision/__init__.py

@@ -29,6 +29,7 @@ from supervision.annotators.core import (
     RichLabelAnnotator,
     RoundBoxAnnotator,
     TraceAnnotator,
+    SplineAnnotator,
     TriangleAnnotator,
 )
 from supervision.annotators.utils import ColorLookup

supervision/annotators/core.py

@@ -7,6 +7,7 @@ import cv2
 import numpy as np
 import numpy.typing as npt
 from PIL import Image, ImageDraw, ImageFont
+from scipy.interpolate import splprep, splev
 
 from supervision.annotators.base import BaseAnnotator, ImageType
 from supervision.annotators.utils import (
@@ -1908,6 +1909,7 @@ class TraceAnnotator(BaseAnnotator):
                 else custom_color_lookup,
             )
             xy = self.trace.get(tracker_id=tracker_id)
+
             if len(xy) > 1:
                 scene = cv2.polylines(
                     scene,
@@ -1918,6 +1920,86 @@ class TraceAnnotator(BaseAnnotator):
                 )
         return scene
 
+class SplineAnnotator(BaseAnnotator):
+    """
+    A class for drawing trace paths on an image based on detection coordinates.
+
+    !!! warning
+
+        This annotator uses the `sv.Detections.tracker_id`. Read
+        [here](/latest/trackers/) to learn how to plug
+        tracking into your inference pipeline.
+    """
+
+    def __init__(
+        self,
+        color: Color | ColorPalette = ColorPalette.DEFAULT,
+        position: Position = Position.CENTER,
+        trace_length: int = 30,
+        thickness: int = 2,
+        color_lookup: ColorLookup = ColorLookup.CLASS,
+    ):
+        """
+        Args:
+            color (Union[Color, ColorPalette]): The color to draw the trace, can be
+                a single color or a color palette.
+            position (Position): The position of the trace.
+                Defaults to `CENTER`.
+            trace_length (int): The maximum length of the trace in terms of historical
+                points. Defaults to `30`.
+            thickness (int): The thickness of the trace lines. Defaults to `2`.
+            color_lookup (ColorLookup): Strategy for mapping colors to annotations.
+                Options are `INDEX`, `CLASS`, `TRACK`.
+        """
+        self.color: Color | ColorPalette = color
+        self.trace = Trace(max_size=trace_length, anchor=position)
+        self.thickness = thickness
+        self.color_lookup: ColorLookup = color_lookup
+
+    @ensure_cv2_image_for_annotation
+    def annotate(self, scene: ImageType, detections: Detections, custom_color_lookup: np.ndarray | None = None) -> ImageType:
+        assert isinstance(scene, np.ndarray)
+
+        if detections.tracker_id is None:
+            raise ValueError(
+                "The `tracker_id` field is missing in the provided detections."
+                " See more: https://supervision.roboflow.com/latest/how_to/track_objects"
+            )
+        
+        detections = detections[detections.tracker_id != PENDING_TRACK_ID]
+
+        self.trace.put(detections)
+        
+        for detection_idx in range(len(detections)):
+            tracker_id = int(detections.tracker_id[detection_idx])
+            color = resolve_color(
+                color=self.color,
+                detections=detections,
+                detection_idx=detection_idx,
+                color_lookup=self.color_lookup
+                if custom_color_lookup is None
+                else custom_color_lookup,
+            )
+            xy = self.trace.get(tracker_id=tracker_id)
+            spline_points = None;
+
+            if len(xy) > 3:
+                x, y = xy[:, 0], xy[:, 1]
+                tck, u = splprep([x, y], s=100)
+                x_new, y_new = splev(np.linspace(0, 1, 100), tck)
+                spline_points = np.stack([x_new, y_new], axis=1).astype(np.int32)
+            else:
+                spline_points = xy.astype(np.int32)
+
+            if len(xy) > 1:
+                scene = cv2.polylines(
+                    scene,
+                    [spline_points],
+                    False,
+                    color=color.as_bgr(),
+                    thickness=self.thickness,
+                )
+        return scene
 
 class HeatMapAnnotator(BaseAnnotator):
     """