[geos-commits] [SCM] GEOS branch main updated. 9bc6ca8716552f8d35e90cd22be433123c06b175

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- Log -----------------------------------------------------------------
commit 9bc6ca8716552f8d35e90cd22be433123c06b175
Author: Paul Ramsey <pramsey at cleverelephant.ca>
Date:   Fri Feb 6 11:47:36 2026 -0800

    Fix: Preserve dimension and type for empty geometries during snap/simplify
    
    Closes https://github.com/libgeos/geos/issues/1356
    
    When performing operations like Snap on empty geometries (e.g., POINT EMPTY, LINESTRING EMPTY, POLYGON EMPTY), the GEOS library was incorrectly modifying their coordinate dimension (e.g., adding a Z dimension) and sometimes changing their type (e.g., POLYGON EMPTY becoming a LinearRing or GeometryCollection).
    
    This fix modifies GeometryTransformer to short-circuit the transformation process if the input geometry is already empty. Instead of transforming it, it now returns a direct clone of the empty input geometry. This ensures that the original type and coordinate dimension (e.g., 2D) are preserved, aligning with the expected behavior for empty geometries.

diff --git a/src/geom/util/GeometryTransformer.cpp b/src/geom/util/GeometryTransformer.cpp
index acec018bf..afa01ce32 100644
--- a/src/geom/util/GeometryTransformer.cpp
+++ b/src/geom/util/GeometryTransformer.cpp
@@ -79,6 +79,11 @@ GeometryTransformer::transform(const Geometry* nInputGeom)
     inputGeom = nInputGeom;
     factory = inputGeom->getFactory();
 
+    // If the input geometry is empty, return a clone of it to preserve its type and dimension
+    if (inputGeom->isEmpty()) {
+        return inputGeom->clone();
+    }
+
     if(const Point* p = dynamic_cast<const Point*>(inputGeom)) {
         return transformPoint(p, nullptr);
     }
diff --git a/tests/unit/operation/overlay/snap/GeometrySnapperTest.cpp b/tests/unit/operation/overlay/snap/GeometrySnapperTest.cpp
index ef82353e3..9e5245436 100644
--- a/tests/unit/operation/overlay/snap/GeometrySnapperTest.cpp
+++ b/tests/unit/operation/overlay/snap/GeometrySnapperTest.cpp
@@ -76,5 +76,56 @@ void object::test<3> ()
     ensure_equals_geometry(expected.get(), result.get());
 }
 
+// Test snapping of empty geometries -- POINT EMPTY
+template<>
+template<>
+void object::test<4> ()
+{
+    std::string wkt = "POINT EMPTY";
+    auto src = reader.read(wkt);
+    GeometrySnapper snapper(*src);
+    auto snap = reader.read(wkt); // Snap against itself
+    auto result = snapper.snapTo(*snap, 1);
+    auto expected = reader.read(wkt);
+
+    ensure_equals_geometry(expected.get(), result.get());
+    ensure_equals(result->getCoordinateDimension(), 2);
+    ensure_equals(result->getGeometryType(), "Point");
+}
+
+// Test snapping of empty geometries -- LINESTRING EMPTY
+template<>
+template<>
+void object::test<5> ()
+{
+    std::string wkt = "LINESTRING EMPTY";
+    auto src = reader.read(wkt);
+    GeometrySnapper snapper(*src);
+    auto snap = reader.read(wkt); // Snap against itself
+    auto result = snapper.snapTo(*snap, 1);
+    auto expected = reader.read(wkt);
+
+    ensure_equals_geometry(expected.get(), result.get());
+    ensure_equals(result->getCoordinateDimension(), 2);
+    ensure_equals(result->getGeometryType(), "LineString");
+}
+
+// Test snapping of empty geometries -- POLYGON EMPTY
+template<>
+template<>
+void object::test<6> ()
+{
+    std::string wkt = "POLYGON EMPTY";
+    auto src = reader.read(wkt);
+    GeometrySnapper snapper(*src);
+    auto snap = reader.read(wkt); // Snap against itself
+    auto result = snapper.snapTo(*snap, 1);
+    auto expected = reader.read(wkt);
+
+    ensure_equals_geometry(expected.get(), result.get());
+    ensure_equals(result->getCoordinateDimension(), 2);
+    ensure_equals(result->getGeometryType(), "Polygon");
+}
+
 
 } // namespace tut

-----------------------------------------------------------------------

Summary of changes:
 src/geom/util/GeometryTransformer.cpp              |  5 +++
 .../operation/overlay/snap/GeometrySnapperTest.cpp | 51 ++++++++++++++++++++++
 2 files changed, 56 insertions(+)


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