fix get_dimensions()

Return values that are consistent with shapely for collections.

src/geography.cpp

@@ -8,6 +8,7 @@
 #include <s2/s2point.h>
 #include <s2/s2polygon.h>
 #include <s2/util/coding/coder.h>
+#include <s2geography/accessors.h>
 #include <s2geography/geography.h>
 #include <s2geography/predicates.h>
 #include <s2geography/wkt-writer.h>
@@ -228,7 +229,11 @@ std::int8_t get_type_id(PyObjectGeography obj) {
 }
 
 int get_dimensions(PyObjectGeography obj) {
-    return obj.as_geog_ptr()->dimension();
+    // note: in case of a collection with features of different dimensions:
+    // - Geography::dimension() returns -1
+    // - s2geography::s2_dimension(geog) returns the max value found in collection
+    // => we want the latter here.
+    return s2geog::s2_dimension(obj.as_geog_ptr()->geog());
 }
 
 /*
@@ -340,15 +345,18 @@ void init_geography(py::module &m) {
     m.def("get_dimensions", py::vectorize(&get_dimensions), py::arg("geography"), R"pbdoc(
         Returns the inherent dimensionality of a geography.
 
-        The inherent dimension is 0 for points, 1 for linestrings and 2 for
-        polygons. For geometrycollections it is the max of the containing elements.
-        Empty collections and None values return -1.
-
         Parameters
         ----------
         geography : :py:class:`Geography` or array_like
             Geography object(s)
 
+        Returns
+        -------
+        dimensions : int or array
+            The inherent dimension is 0 for points, 1 for linestrings and 2 for
+            polygons. For geometrycollections it is either the max of the containing
+            elements or -1 for empty collections.
+
     )pbdoc");
 
     // Geography utils

tests/test_geography.py

@@ -85,6 +85,26 @@ def test_get_dimensions() -> None:
     assert spherely.get_dimensions(spherely.create_point(5, 40)) == 0
 
 
+@pytest.mark.parametrize(
+    "empty_geog, expected",
+    [
+        (spherely.create_point(), 0),
+        (spherely.create_linestring(), 1),
+        (spherely.create_polygon(), 2),
+        (spherely.create_collection([]), -1),
+    ],
+)
+def test_get_dimensions_empty(empty_geog, expected) -> None:
+    assert spherely.get_dimensions(empty_geog) == expected
+
+
+def test_get_dimensions_collection() -> None:
+    geog = spherely.create_collection(
+        [spherely.create_point(0, 0), spherely.create_polygon([(0, 0), (1, 1), (2, 0)])]
+    )
+    assert spherely.get_dimensions(geog) == 2
+
+
 def test_prepare() -> None:
     # test array
     geog = np.array(