Added Geometry Validation, Geometry Metadata, and WKT instead of Python str() to GeoDataFrame Loader (#9466)

@rlancemartin The current implementation within `Geopandas.GeoDataFrame`
loader uses the python builtin `str()` function on the input geometries.
While this looks very close to WKT (Well known text), Python's str
function doesn't guarantee that.

In the interest of interop., I've changed to the of use `wkt` property
on the Shapely geometries for generating the text representation of the
geometries.

Also, included here:
- validation of the input `page_content_column` as being a GeoSeries.
- geometry `crs` (Coordinate Reference System) / bounds
(xmin/ymin/xmax/ymax) added to Document metadata. Having the CRS is
critical... having the bounds is just helpful!

I think there is a larger question of "Should the geometry live in the
`page_content`, or should the record be better summarized and tuck the
geom into metadata?" ...something for another day and another PR.

libs/langchain/langchain/document_loaders/geodataframe.py

@@ -29,19 +29,43 @@ class GeoDataFrameLoader(BaseLoader):
                 f"Expected data_frame to be a gpd.GeoDataFrame, got {type(data_frame)}"
             )
 
+        if page_content_column not in data_frame.columns:
+            raise ValueError(
+                f"Expected data_frame to have a column named {page_content_column}"
+            )
+
+        if not isinstance(data_frame[page_content_column].iloc[0], gpd.GeoSeries):
+            raise ValueError(
+                f"Expected data_frame[{page_content_column}] to be a GeoSeries"
+            )
+
         self.data_frame = data_frame
         self.page_content_column = page_content_column
 
     def lazy_load(self) -> Iterator[Document]:
         """Lazy load records from dataframe."""
 
+        # assumes all geometries in GeoSeries are same CRS and Geom Type
+        crs_str = self.data_frame.crs.to_string() if self.data_frame.crs else None
+        geometry_type = self.data_frame.geometry.geom_type.iloc[0]
+
         for _, row in self.data_frame.iterrows():
-            text = row[self.page_content_column]
+            geom = row[self.page_content_column]
+
+            xmin, ymin, xmax, ymax = geom.bounds
+
             metadata = row.to_dict()
+            metadata["crs"] = crs_str
+            metadata["geometry_type"] = geometry_type
+            metadata["xmin"] = xmin
+            metadata["ymin"] = ymin
+            metadata["xmax"] = xmax
+            metadata["ymax"] = ymax
+
             metadata.pop(self.page_content_column)
-            # Enforce str since shapely Point objects
-            # geometry type used in GeoPandas) are not strings
-            yield Document(page_content=str(text), metadata=metadata)
+
+            # using WKT instead of str() to help GIS system interoperability
+            yield Document(page_content=geom.wkt, metadata=metadata)
 
     def load(self) -> List[Document]:
         """Load full dataframe."""

libs/langchain/tests/integration_tests/document_loaders/test_geodataframe.py

@@ -17,6 +17,7 @@ else:
 def sample_gdf() -> GeoDataFrame:
     import geopandas
 
+    # TODO: geopandas.datasets will be deprecated in 1.0
     path_to_data = geopandas.datasets.get_path("nybb")
     gdf = geopandas.read_file(path_to_data)
     gdf["area"] = gdf.area