Add function to create geometry collection from OSM data

Creates a geometry collection from relations, more specifically their
member nodes and ways. Member relations are ignored.

Author: joto

src/geom-from-osm.cpp

@@ -173,4 +173,38 @@ geometry_t create_multipolygon(osmium::Relation const &relation,
     return geom;
 }
 
+void create_collection(geometry_t *geom,
+                       osmium::memory::Buffer const &member_buffer)
+{
+    auto &collection = geom->set<collection_t>();
+
+    for (auto const &obj : member_buffer) {
+        if (obj.type() == osmium::item_type::node) {
+            auto const &node = static_cast<osmium::Node const &>(obj);
+            if (node.location().valid()) {
+                collection.add_geometry(create_point(node));
+            }
+        } else if (obj.type() == osmium::item_type::way) {
+            auto const &way = static_cast<osmium::Way const &>(obj);
+            geometry_t item;
+            auto &line = item.set<linestring_t>();
+            fill_point_list(&line, way.nodes());
+            if (line.size() >= 2U) {
+                collection.add_geometry(std::move(item));
+            }
+        }
+    }
+
+    if (collection.num_geometries() == 0) {
+        geom->reset();
+    }
+}
+
+geometry_t create_collection(osmium::memory::Buffer const &member_buffer)
+{
+    geometry_t geom{};
+    create_collection(&geom, member_buffer);
+    return geom;
+}
+
 } // namespace geom

src/geom-from-osm.hpp

@@ -142,6 +142,30 @@ void create_multipolygon(geometry_t *geom, osmium::Relation const &relation,
 geometry_t create_multipolygon(osmium::Relation const &relation,
                                osmium::memory::Buffer const &way_buffer);
 
+/**
+ * Create a geometry collection from a relation and node/way members.
+ *
+ * If the resulting geometry would be empty or invalid, a null geometry is
+ * returned.
+ *
+ * \param geom Pointer to an existing geometry which will be used as output.
+ * \param relation The input relation.
+ * \param way_buffer Buffer containing all member nodes and ways.
+ */
+void create_collection(geometry_t *geom,
+                       osmium::memory::Buffer const &member_buffer);
+
+/**
+ * Create a geometry collection from a relation and node/way members.
+ *
+ * If the resulting geometry would be empty or invalid, a null geometry is
+ * returned.
+ *
+ * \param way_buffer Buffer containing all member nodes and ways.
+ * \returns The created geometry.
+ */
+geometry_t create_collection(osmium::memory::Buffer const &member_buffer);
+
 } // namespace geom
 
 #endif // OSM2PGSQL_GEOM_FROM_OSM_HPP

src/geom-functions.cpp

@@ -554,7 +554,8 @@ geometry_t centroid(geometry_t const &geom)
     geom.visit(overloaded{
         [&](geom::nullgeom_t const & /*input*/) { output.reset(); },
         [&](geom::collection_t const & /*input*/) {
-            throw std::runtime_error{"not implemented yet"};
+            throw std::runtime_error{
+                "Centroid of geometry collection not implemented yet"};
         },
         [&](auto const &input) { boost::geometry::centroid(input, center); }});
 

tests/CMakeLists.txt

@@ -44,6 +44,7 @@ set_test(test-domain-matcher LABELS NoDB)
 set_test(test-expire-tiles LABELS NoDB)
 set_test(test-geom-box LABELS NoDB)
 set_test(test-geom-lines LABELS NoDB)
+set_test(test-geom-collections LABELS NoDB)
 set_test(test-geom-null LABELS NoDB)
 set_test(test-geom-points LABELS NoDB)
 set_test(test-geom-polygons LABELS NoDB)

tests/test-geom-collections.cpp

@@ -0,0 +1,78 @@
+/**
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * This file is part of osm2pgsql (https://osm2pgsql.org/).
+ *
+ * Copyright (C) 2006-2022 by the osm2pgsql developer community.
+ * For a full list of authors see the git log.
+ */
+
+#include <catch.hpp>
+
+#include "common-buffer.hpp"
+
+#include "geom-from-osm.hpp"
+#include "geom-functions.hpp"
+#include "geom.hpp"
+
+TEST_CASE("geometry collection with point", "[NoDB]")
+{
+    geom::geometry_t geom{geom::collection_t{}};
+    auto &c = geom.get<geom::collection_t>();
+
+    c.add_geometry(geom::geometry_t{geom::point_t{1, 1}});
+
+    REQUIRE(geometry_type(geom) == "GEOMETRYCOLLECTION");
+    REQUIRE(num_geometries(geom) == 1);
+    REQUIRE(area(geom) == Approx(0.0));
+    REQUIRE_THROWS(centroid(geom));
+}
+
+TEST_CASE("geometry collection with several geometries", "[NoDB]")
+{
+    geom::geometry_t geom{geom::collection_t{}};
+    auto &c = geom.get<geom::collection_t>();
+
+    c.add_geometry(geom::geometry_t{geom::point_t{1, 1}});
+    c.add_geometry(geom::geometry_t{geom::linestring_t{{1, 1}, {2, 2}}});
+    c.add_geometry(geom::geometry_t{geom::point_t{2, 2}});
+
+    REQUIRE(geometry_type(geom) == "GEOMETRYCOLLECTION");
+    REQUIRE(num_geometries(geom) == 3);
+    REQUIRE(area(geom) == Approx(0.0));
+    REQUIRE_THROWS(centroid(geom));
+}
+
+TEST_CASE("create_collection from OSM data", "[NoDB]")
+{
+    test_buffer_t buffer;
+    buffer.add_node("n1 x1 y1");
+    buffer.add_way("w20 Nn1x1y1,n2x2y1,n3x2y2,n4x1y2,n1x1y1");
+    buffer.add_way("w21 Nn5x10y10,n6x10y20");
+    buffer.add_relation("r30 Mw20@");
+
+    auto const geom = geom::create_collection(buffer.buffer());
+
+    REQUIRE(geometry_type(geom) == "GEOMETRYCOLLECTION");
+    REQUIRE(num_geometries(geom) == 3);
+
+    auto const &c = geom.get<geom::collection_t>();
+    REQUIRE(c[0] == geom::geometry_t{geom::point_t{1, 1}});
+    REQUIRE(c[1] == geom::geometry_t{geom::linestring_t{
+                        {1, 1}, {2, 1}, {2, 2}, {1, 2}, {1, 1}}});
+    REQUIRE(c[2] == geom::geometry_t{geom::linestring_t{{10, 10}, {10, 20}}});
+
+    REQUIRE(area(geom) == Approx(0.0));
+    REQUIRE_THROWS(centroid(geom));
+}
+
+TEST_CASE("create_collection from no OSM data returns null geometry", "[NoDB]")
+{
+    test_buffer_t buffer;
+    buffer.add_relation("r30 Mw20@");
+
+    auto const geom = geom::create_collection(buffer.buffer());
+
+    REQUIRE(geometry_type(geom) == "NULL");
+    REQUIRE(num_geometries(geom) == 0);
+}