Warn on missing CRS (#395)

Closes #371

lonboard/_geoarrow/ops/reproject.py

@@ -5,6 +5,7 @@
 from concurrent.futures import ThreadPoolExecutor
 from functools import lru_cache, partial
 from typing import Callable, Optional, Tuple, Union
+from warnings import warn
 
 import numpy as np
 import pyarrow as pa
@@ -18,6 +19,13 @@
 TransformerFromCRS = lru_cache(Transformer.from_crs)
 
 
+def no_crs_warning():
+    warn(
+        "No CRS exists on data. "
+        "If no data is shown on the map, double check that your CRS is WGS84."
+    )
+
+
 def reproject_table(
     table: pa.Table,
     *,
@@ -44,6 +52,7 @@ def reproject_table(
 
     # geometry column exists in table but is not assigned a CRS
     if b"ARROW:extension:metadata" not in geom_field.metadata:
+        no_crs_warning()
         return table
 
     new_field, new_column = reproject_column(
@@ -70,6 +79,7 @@ def reproject_column(
     extension_type_name = field.metadata[b"ARROW:extension:name"]
     crs_str = get_field_crs(field)
     if crs_str is None:
+        no_crs_warning()
         return field, column
 
     existing_crs = CRS(crs_str)

tests/test_layer.py

@@ -7,7 +7,8 @@
 from pyogrio.raw import read_arrow
 from traitlets import TraitError
 
-from lonboard import BitmapLayer, Map, ScatterplotLayer, SolidPolygonLayer
+from lonboard import BitmapLayer, Map, ScatterplotLayer, SolidPolygonLayer, viz
+from lonboard._geoarrow.geopandas_interop import geopandas_to_geoarrow
 from lonboard.layer_extension import DataFilterExtension
 
 
@@ -93,6 +94,27 @@ def test_layer_wkb_geoarrow_wrong_geom_type():
         _layer = ScatterplotLayer(table=table)
 
 
+def test_warning_no_crs_shapely():
+    points = shapely.points([0, 1, 2], [2, 3, 4])
+    with pytest.warns(match="No CRS exists on data"):
+        _ = viz(points)
+
+
+def test_warning_no_crs_geopandas():
+    points = shapely.points([0, 1, 2], [2, 3, 4])
+    gdf = gpd.GeoDataFrame(geometry=points)
+    with pytest.warns(match="No CRS exists on data"):
+        _ = viz(gdf)
+
+
+def test_warning_no_crs_arrow():
+    points = shapely.points([0, 1, 2], [2, 3, 4])
+    gdf = gpd.GeoDataFrame(geometry=points)
+    table = geopandas_to_geoarrow(gdf)
+    with pytest.warns(match="No CRS exists on data"):
+        _ = viz(table)
+
+
 # Test layer types
 def test_bitmap_layer():
     layer = BitmapLayer(