Implement save/load methods for RegionOfInterest objects

Author: Tushar7012

movement/roi/base.py

@@ -2,8 +2,10 @@
 
 from __future__ import annotations
 
+import json
 from abc import ABC, abstractmethod
 from collections.abc import Callable, Hashable, Sequence
+from pathlib import Path
 from typing import TYPE_CHECKING, Any, Generic, TypeAlias, TypeVar, cast
 
 import matplotlib.pyplot as plt
@@ -560,3 +562,81 @@ def plot(
         if fig is None or ax is None:
             fig, ax = plt.subplots(1, 1)
         return self._plot(fig, ax, **matplotlib_kwargs)
+
+    def to_file(self, path: str | Path) -> None:
+        """Save the region of interest to a file.
+
+        Parameters
+        ----------
+        path : str | Path
+            Path to save the ROI file. The file will be saved in JSON format.
+
+        See Also
+        --------
+        from_file : Load a region of interest from a file.
+
+        Examples
+        --------
+        >>> from movement.roi import PolygonOfInterest
+        >>> roi = PolygonOfInterest([(0, 0), (1, 0), (1, 1)], name="triangle")
+        >>> roi.to_file("my_roi.json")  # doctest: +SKIP
+
+        """
+        data = {
+            "name": self._name,
+            "geometry_wkt": self.region.wkt,
+            "dimensions": self.dimensions,
+            "roi_type": self.__class__.__name__,
+        }
+        Path(path).write_text(json.dumps(data, indent=2))
+
+    @classmethod
+    def from_file(cls, path: str | Path) -> BaseRegionOfInterest:
+        """Load a region of interest from a file.
+
+        Parameters
+        ----------
+        path : str | Path
+            Path to the ROI file to load. Must be a JSON file saved by
+            :meth:`to_file`.
+
+        Returns
+        -------
+        BaseRegionOfInterest
+            The loaded region of interest object. The specific subclass
+            (LineOfInterest or PolygonOfInterest) is determined from the file.
+
+        Raises
+        ------
+        FileNotFoundError
+            If the specified file does not exist.
+
+        See Also
+        --------
+        to_file : Save a region of interest to a file.
+
+        Examples
+        --------
+        >>> from movement.roi import PolygonOfInterest
+        >>> roi = PolygonOfInterest.from_file("my_roi.json")  # doctest: +SKIP
+
+        """
+        file_path = Path(path)
+        if not file_path.exists():
+            raise FileNotFoundError(f"ROI file not found: {path}")
+
+        data = json.loads(file_path.read_text())
+        geometry = shapely.from_wkt(data["geometry_wkt"])
+
+        # Import here to avoid circular imports
+        from movement.roi import LineOfInterest, PolygonOfInterest
+
+        roi_type = data.get("roi_type", "")
+        if roi_type == "LineOfInterest" or data["dimensions"] == 1:
+            return LineOfInterest._from_geometry(
+                geometry, name=data.get("name")
+            )
+        else:
+            return PolygonOfInterest._from_geometry(
+                geometry, name=data.get("name")
+            )

movement/roi/line.py

@@ -84,6 +84,31 @@ def __init__(
         line = shapely.normalize(line)
         super().__init__(line, name=name)
 
+    @classmethod
+    def _from_geometry(
+        cls,
+        geometry: "shapely.LineString | shapely.LinearRing",
+        name: str | None = None,
+    ) -> "LineOfInterest":
+        """Construct a LineOfInterest from a shapely geometry.
+
+        Parameters
+        ----------
+        geometry : shapely.LineString | shapely.LinearRing
+            The shapely geometry to construct from.
+        name : str, optional
+            Name for the LineOfInterest.
+
+        Returns
+        -------
+        LineOfInterest
+            A new LineOfInterest instance.
+
+        """
+        points = geometry.coords
+        loop = isinstance(geometry, shapely.LinearRing)
+        return cls(points=points, loop=loop, name=name)
+
     def _plot(
         self, fig: Figure | SubFigure, ax: Axes, **matplotlib_kwargs
     ) -> tuple[Figure | SubFigure, Axes]:

movement/roi/polygon.py

@@ -85,6 +85,35 @@ def __init__(
         )
         super().__init__(geometry=polygon, name=name)
 
+    @classmethod
+    def _from_geometry(
+        cls,
+        geometry: shapely.Polygon,
+        name: str | None = None,
+    ) -> PolygonOfInterest:
+        """Construct a PolygonOfInterest from a shapely geometry.
+
+        Parameters
+        ----------
+        geometry : shapely.Polygon
+            The shapely geometry to construct from.
+        name : str, optional
+            Name for the PolygonOfInterest.
+
+        Returns
+        -------
+        PolygonOfInterest
+            A new PolygonOfInterest instance.
+
+        """
+        exterior = geometry.exterior.coords
+        holes = (
+            [interior.coords for interior in geometry.interiors]
+            if geometry.interiors
+            else None
+        )
+        return cls(exterior_boundary=exterior, holes=holes, name=name)
+
     @property
     def _default_plot_args(self) -> dict[str, Any]:
         return {

tests/test_unit/test_roi/test_save_load.py

@@ -0,0 +1,86 @@
+"""Tests for saving and loading regions of interest to/from files."""
+
+import json
+
+import pytest
+
+from movement.roi import LineOfInterest, PolygonOfInterest
+
+
+class TestROISaveLoad:
+    """Tests for ROI save/load functionality."""
+
+    def test_save_and_load_polygon_roi(self, tmp_path, triangle):
+        """Test round-trip save and load for PolygonOfInterest."""
+        file_path = tmp_path / "triangle.json"
+
+        # Save
+        triangle.to_file(file_path)
+
+        # Verify file exists and has correct content
+        assert file_path.exists()
+        data = json.loads(file_path.read_text())
+        assert data["roi_type"] == "PolygonOfInterest"
+        assert data["dimensions"] == 2
+        assert data["name"] == "triangle"
+        assert "geometry_wkt" in data
+
+        # Load
+        loaded = PolygonOfInterest.from_file(file_path)
+
+        # Verify loaded ROI matches original
+        assert loaded.name == triangle.name
+        assert loaded.dimensions == triangle.dimensions
+        assert loaded.region.equals(triangle.region)
+
+    def test_save_and_load_line_roi(self, tmp_path, segment_of_y_equals_x):
+        """Test round-trip save and load for LineOfInterest."""
+        file_path = tmp_path / "line.json"
+
+        # Save
+        segment_of_y_equals_x.to_file(file_path)
+
+        # Verify file exists
+        assert file_path.exists()
+        data = json.loads(file_path.read_text())
+        assert data["roi_type"] == "LineOfInterest"
+        assert data["dimensions"] == 1
+
+        # Load
+        loaded = LineOfInterest.from_file(file_path)
+
+        # Verify loaded ROI matches original
+        assert loaded.dimensions == segment_of_y_equals_x.dimensions
+        assert loaded.region.equals(segment_of_y_equals_x.region)
+
+    def test_save_and_load_polygon_with_hole(
+        self, tmp_path, unit_square_with_hole
+    ):
+        """Test round-trip for polygon with interior holes."""
+        file_path = tmp_path / "square_with_hole.json"
+
+        # Save
+        unit_square_with_hole.to_file(file_path)
+
+        # Load
+        loaded = PolygonOfInterest.from_file(file_path)
+
+        # Verify holes are preserved
+        assert loaded.region.equals(unit_square_with_hole.region)
+        assert len(loaded.holes) == len(unit_square_with_hole.holes)
+
+    def test_load_nonexistent_file_raises(self, tmp_path):
+        """Test that loading a non-existent file raises FileNotFoundError."""
+        with pytest.raises(FileNotFoundError, match="ROI file not found"):
+            PolygonOfInterest.from_file(tmp_path / "nonexistent.json")
+
+    def test_save_with_none_name(self, tmp_path, triangle_pts):
+        """Test saving an ROI with no name."""
+        roi = PolygonOfInterest(triangle_pts)  # No name provided
+        file_path = tmp_path / "unnamed.json"
+
+        roi.to_file(file_path)
+        loaded = PolygonOfInterest.from_file(file_path)
+
+        # Name should be None in both
+        assert loaded._name is None