Tidy GeometryFlattener

include/geos/operation/cluster/GeometryFlattener.h

@@ -26,34 +26,18 @@ namespace cluster {
 
 class GEOS_DLL GeometryFlattener {
 public:
-    static std::unique_ptr<geom::Geometry>
-    flatten(std::unique_ptr<geom::Geometry>&& g) {
-        if (!g->isCollection()) {
-            return std::move(g);
-        }
-
-        const geom::GeometryFactory* factory = g->getFactory();
-
-        std::vector<std::unique_ptr<geom::Geometry>> components;
-        flatten(std::move(g), components);
-
-        return factory->buildGeometry(std::move(components));
-    };
-
-    static void
-    flatten(std::unique_ptr<geom::Geometry>&& g, std::vector<std::unique_ptr<geom::Geometry>> & components)
-    {
-        if (g->isCollection()) {
-            auto gc = static_cast<geom::GeometryCollection*>(g.get());
-
-            for (auto& gi : gc->releaseGeometries()) {
-                flatten(std::move(gi), components);
-            }
-        } else {
-            components.push_back(std::move(g));
-        }
-    };
-
+    /** Flatten a geometry such that it contains no nested components (e.g., MultiPolygons within
+     *  GeometryCollections, etc.). The flattened geometry will use the most narrow representation
+     *  possible (Polygon preferred to MultiPolygon, MultiPolygon preferred to GeometryCollection.)
+     *
+     * @brief flatten
+     * @param g a geometry to be flattened; consumed by the function
+     * @return a geometry with no nested components
+     */
+    static std::unique_ptr<geom::Geometry> flatten(std::unique_ptr<geom::Geometry>&& g);
+
+private:
+    static void flatten(std::unique_ptr<geom::Geometry>&& g, std::vector<std::unique_ptr<geom::Geometry>>& components);
 };
 
 

src/operation/cluster/GeometryFlattener.cpp

@@ -0,0 +1,56 @@
+/**********************************************************************
+ *
+ * GEOS - Geometry Engine Open Source
+ * http://geos.osgeo.org
+ *
+ * Copyright (C) 2022 ISciences LLC
+ *
+ * This is free software; you can redistribute and/or modify it under
+ * the terms of the GNU Lesser General Public Licence as published
+ * by the Free Software Foundation.
+ * See the COPYING file for more information.
+ *
+ **********************************************************************/
+
+#include <geos/operation/cluster/GeometryFlattener.h>
+
+namespace geos  {
+namespace operation {
+namespace cluster {
+
+std::unique_ptr<geom::Geometry>
+GeometryFlattener::flatten(std::unique_ptr<geom::Geometry>&& g) {
+    if (!g->isCollection()) {
+        return std::move(g);
+    }
+
+    if (g->isEmpty()) {
+        return std::move(g);
+    }
+
+    const geom::GeometryFactory* factory = g->getFactory();
+
+    std::vector<std::unique_ptr<geom::Geometry>> components;
+    flatten(std::move(g), components);
+
+    return factory->buildGeometry(std::move(components));
+}
+
+void
+GeometryFlattener::flatten(std::unique_ptr<geom::Geometry>&& g, std::vector<std::unique_ptr<geom::Geometry>>& components)
+{
+    if (g->isCollection()) {
+        auto gc = static_cast<geom::GeometryCollection*>(g.get());
+
+        for (auto& gi : gc->releaseGeometries()) {
+            flatten(std::move(gi), components);
+        }
+    } else {
+        components.push_back(std::move(g));
+    }
+}
+
+
+}
+}
+}

tests/unit/operation/cluster/ClusterTest.cpp

@@ -1,5 +1,5 @@
 //
-// Test Suite for geos::operation::cluster::Cluster class.
+// Test Suite for geos::operation::cluster::ClusterFinder classes
 
 // tut
 #include <tut/tut.hpp>

tests/unit/operation/cluster/GeometryFlattenerTest.cpp

@@ -0,0 +1,81 @@
+//
+// Test Suite for geos::operation::cluster::GeometryFlattener class.
+
+// tut
+#include <tut/tut.hpp>
+// geos
+#include <geos/operation/cluster/GeometryFlattener.h>
+#include <geos/io/WKTReader.h>
+
+namespace tut {
+//
+// Test Group
+//
+
+// Common data used by tests
+struct test_flattener_data {
+    geos::io::WKTReader reader;
+
+    void checkFlattener(const std::string& input_wkt, const std::string& expected_wkt) {
+        const auto& flattened = geos::operation::cluster::GeometryFlattener::flatten(reader.read(input_wkt));
+        const auto& expected = reader.read(expected_wkt);
+
+        ensure_equals(flattened->getGeometryType(), expected->getGeometryType());
+        ensure(flattened->equals(expected.get()));
+    }
+
+    void checkFlattenerUnchanged(const std::string& input_wkt) {
+        checkFlattener(input_wkt, input_wkt);
+    }
+};
+
+typedef test_group<test_flattener_data> group;
+typedef group::object object;
+
+group test_flattenerrtest_group("geos::operation::cluster::GeometryFlattener");
+
+// empty geometry unchanged
+template<>
+template<>
+void object::test<1>()
+{
+    checkFlattenerUnchanged("POINT EMPTY");
+    checkFlattenerUnchanged("LINESTRING EMPTY");
+    checkFlattenerUnchanged("POLYGON EMPTY");
+    checkFlattenerUnchanged("MULTIPOINT EMPTY");
+    checkFlattenerUnchanged("MULTILINESTRING EMPTY");
+    checkFlattenerUnchanged("MULTIPOLYGON EMPTY");
+    checkFlattenerUnchanged("GEOMETRYCOLLECTION EMPTY");
+}
+
+// single-part geometry unchanged
+template<>
+template<>
+void object::test<2>()
+{
+    checkFlattenerUnchanged("POINT (3 8)");
+    checkFlattenerUnchanged("LINESTRING (3 8, 2 2)");
+    checkFlattenerUnchanged("POLYGON ((0 0, 0 1, 1 1, 0 0))");
+}
+
+// single-part collections simplified
+template<>
+template<>
+void object::test<3>()
+{
+    checkFlattener("GEOMETRYCOLLECTION (POINT (1 1))", "POINT (1 1)");
+    checkFlattener("MULTIPOINT (1 1)", "POINT (1 1)");
+}
+
+// most narrow representation used
+template<>
+template<>
+void object::test<4>()
+{
+    checkFlattener("GEOMETRYCOLLECTION (POINT (1 1), MULTIPOINT (1 2, 1 3), GEOMETRYCOLLECTION (POINT (1 4), POINT EMPTY))",
+                   "MULTIPOINT ((1 1), (1 2), (1 3), (1 4), EMPTY)");
+    checkFlattener("GEOMETRYCOLLECTION(MULTILINESTRING ((1 1, 2 2)), MULTIPOINT ((3 3), (4 4)))",
+                   "GEOMETRYCOLLECTION(LINESTRING (1 1, 2 2), POINT (3 3), POINT (4 4))");
+}
+
+}