Fix GeoDataset pickling (#304)

* Fix GeoDataset pickling

* mypy fixes

tests/datasets/test_geo.py

@@ -2,6 +2,7 @@
 # Licensed under the MIT License.
 
 import os
+import pickle
 from pathlib import Path
 from typing import Dict
 
@@ -121,6 +122,14 @@ def test_str(self, dataset: GeoDataset) -> None:
         assert "bbox: BoundingBox" in out
         assert "size: 1" in out
 
+    def test_picklable(self, dataset: GeoDataset) -> None:
+        x = pickle.dumps(dataset)
+        y = pickle.loads(x)
+        assert dataset.crs == y.crs
+        assert dataset.res == y.res
+        assert len(dataset) == len(y)
+        assert dataset.bounds == y.bounds
+
     def test_abstract(self) -> None:
         with pytest.raises(TypeError, match="Can't instantiate abstract class"):
             GeoDataset()  # type: ignore[abstract]

torchgeo/datasets/geo.py

@@ -172,6 +172,41 @@ def __str__(self) -> str:
     bbox: {self.bounds}
     size: {len(self)}"""
 
+    # NOTE: This hack should be removed once the following issue is fixed:
+    # https://github.com/Toblerity/rtree/issues/87
+
+    def __getstate__(
+        self,
+    ) -> Tuple[
+        Dict[Any, Any],
+        List[Tuple[int, Tuple[float, float, float, float, float, float], str]],
+    ]:
+        """Define how instances are pickled.
+
+        Returns:
+            the state necessary to unpickle the instance
+        """
+        objects = self.index.intersection(self.index.bounds, objects=True)
+        tuples = [(item.id, item.bounds, item.object) for item in objects]
+        return self.__dict__, tuples
+
+    def __setstate__(
+        self,
+        state: Tuple[
+            Dict[Any, Any],
+            List[Tuple[int, Tuple[float, float, float, float, float, float], str]],
+        ],
+    ) -> None:
+        """Define how to unpickle an instance.
+
+        Args:
+            state: the state of the instance when it was pickled
+        """
+        attrs, tuples = state
+        self.__dict__.update(attrs)
+        for item in tuples:
+            self.index.insert(*item)
+
     @property
     def bounds(self) -> BoundingBox:
         """Bounds of the index.