Merge pull request #1760 from joto/geom-add-reverse

Add reverse() function to reverse linestring (and other) geometries

Author: lonvia

src/flex-lua-geom.cpp

@@ -119,6 +119,20 @@ static int geom_is_null(lua_State *lua_state)
     return 1;
 }
 
+static int geom_reverse(lua_State *lua_state)
+{
+    auto const *const input_geometry = unpack_geometry(lua_state);
+
+    try {
+        auto *geom = create_lua_geometry_object(lua_state);
+        geom::reverse(geom, *input_geometry);
+    } catch (...) {
+        return luaL_error(lua_state, "Unknown error in 'reverse()'.\n");
+    }
+
+    return 1;
+}
+
 static int geom_line_merge(lua_State *lua_state)
 {
     auto const *const input_geometry = unpack_geometry(lua_state);
@@ -230,6 +244,7 @@ void init_geometry_class(lua_State *lua_state)
     luaX_add_table_func(lua_state, "geometry_type", geom_geometry_type);
     luaX_add_table_func(lua_state, "is_null", geom_is_null);
     luaX_add_table_func(lua_state, "line_merge", geom_line_merge);
+    luaX_add_table_func(lua_state, "reverse", geom_reverse);
     luaX_add_table_func(lua_state, "num_geometries", geom_num_geometries);
     luaX_add_table_func(lua_state, "segmentize", geom_segmentize);
     luaX_add_table_func(lua_state, "simplify", geom_simplify);

src/geom-functions.cpp

@@ -446,6 +446,62 @@ static void add_nodes_to_linestring(linestring_t *linestring, ITERATOR it,
     }
 }
 
+/****************************************************************************/
+
+static void reverse(geom::nullgeom_t * /*output*/,
+                    geom::nullgeom_t const & /*input*/) noexcept
+{}
+
+static void reverse(geom::point_t *output, geom::point_t const &input) noexcept
+{
+    *output = input;
+}
+
+static void reverse(point_list_t *output, point_list_t const &input)
+{
+    output->reserve(input.size());
+    std::reverse_copy(input.cbegin(), input.cend(),
+                      std::back_inserter(*output));
+}
+
+static void reverse(geom::polygon_t *output, geom::polygon_t const &input)
+{
+    reverse(&output->outer(), input.outer());
+    for (auto const &g : input.inners()) {
+        reverse(&output->inners().emplace_back(), g);
+    }
+}
+
+template <typename T>
+void reverse(geom::multigeometry_t<T> *output,
+             geom::multigeometry_t<T> const &input)
+{
+    output->reserve(input.num_geometries());
+    for (auto const &g : input) {
+        reverse(&output->add_geometry(), g);
+    }
+}
+
+void reverse(geometry_t *output, geometry_t const &input)
+{
+    output->set_srid(input.srid());
+
+    input.visit([&](auto const &geom) {
+        using inner_type =
+            std::remove_const_t<std::remove_reference_t<decltype(geom)>>;
+        return reverse(&output->set<inner_type>(), geom);
+    });
+}
+
+geometry_t reverse(geometry_t const &input)
+{
+    geometry_t output;
+    reverse(&output, input);
+    return output;
+}
+
+/****************************************************************************/
+
 void line_merge(geometry_t *output, geometry_t const &input)
 {
     if (input.is_linestring()) {

src/geom-functions.hpp

@@ -158,6 +158,22 @@ double area(geometry_t const &geom);
  */
 std::vector<geometry_t> split_multi(geometry_t &&geom, bool split_multi = true);
 
+/**
+ * Reverses the order of the vertices in geometry.
+ *
+ * \param output Pointer to output geometry.
+ * \param input Input geometry.
+ */
+void reverse(geometry_t *output, geometry_t const &input);
+
+/**
+ * Reverses the order of the vertices in geometry.
+ *
+ * \param input Input geometry.
+ * \returns Result geometry.
+ */
+geometry_t reverse(geometry_t const &input);
+
 /**
  * Merge lines in a multilinestring end-to-end as far as possible.
  *

tests/test-geom-linestrings.cpp

@@ -49,6 +49,19 @@ TEST_CASE("line geometry", "[NoDB]")
     REQUIRE(geometry_n(geom, 1) == geom);
 }
 
+TEST_CASE("reverse line geometry", "[NoDB]")
+{
+    geom::geometry_t const geom{geom::linestring_t{{1, 1}, {2, 2}}};
+
+    auto reversed = geom::reverse(geom);
+    REQUIRE(num_geometries(reversed) == 1);
+    REQUIRE(geometry_type(reversed) == "LINESTRING");
+
+    auto const &line = reversed.get<geom::linestring_t>();
+    REQUIRE(line.size() == 2);
+    REQUIRE(line == geom::linestring_t{{2, 2}, {1, 1}});
+}
+
 TEST_CASE("create_linestring from OSM data", "[NoDB]")
 {
     test_buffer_t buffer;

tests/test-geom-multilinestrings.cpp

@@ -20,6 +20,7 @@
 TEST_CASE("create_multilinestring with single line", "[NoDB]")
 {
     geom::linestring_t const expected{{1, 1}, {2, 1}};
+    geom::linestring_t const expected_rev{{2, 1}, {1, 1}};
 
     test_buffer_t buffer;
     buffer.add_way("w20 Nn10x1y1,n11x2y1");
@@ -34,6 +35,10 @@ TEST_CASE("create_multilinestring with single line", "[NoDB]")
     auto const &ml = geom.get<geom::multilinestring_t>();
     REQUIRE(ml.num_geometries() == 1);
     REQUIRE(ml[0] == expected);
+
+    auto const rev = reverse(geom);
+    REQUIRE(rev.is_multilinestring());
+    REQUIRE(rev.get<geom::multilinestring_t>()[0] == expected_rev);
 }
 
 TEST_CASE("create_multilinestring with single line and no force_multi",

tests/test-geom-multipoints.cpp

@@ -30,6 +30,7 @@ TEST_CASE("multipoint_t with a single point", "[NoDB]")
     REQUIRE(geometry_type(geom) == "MULTIPOINT");
     REQUIRE(num_geometries(geom) == 1);
     REQUIRE(area(geom) == Approx(0.0));
+    REQUIRE(reverse(geom) == geom);
     REQUIRE(centroid(geom) == geom::geometry_t{std::move(point)});
 
     REQUIRE(mp[0] == expected);
@@ -51,6 +52,7 @@ TEST_CASE("multipoint_t with several points", "[NoDB]")
     REQUIRE(geometry_type(geom) == "MULTIPOINT");
     REQUIRE(num_geometries(geom) == 3);
     REQUIRE(area(geom) == Approx(0.0));
+    REQUIRE(reverse(geom) == geom);
     REQUIRE(centroid(geom) == geom::geometry_t{geom::point_t{2, 1}});
 
     REQUIRE(mp[0] == p0);

tests/test-geom-null.cpp

@@ -22,4 +22,5 @@ TEST_CASE("null geometry", "[NoDB]")
     REQUIRE(geometry_type(geom) == "NULL");
     REQUIRE(centroid(geom).is_null());
     REQUIRE(geometry_n(geom, 1).is_null());
+    REQUIRE(reverse(geom).is_null());
 }

tests/test-geom-points.cpp

@@ -54,6 +54,7 @@ TEST_CASE("create_point from OSM data", "[NoDB]")
     REQUIRE(area(geom) == Approx(0.0));
     REQUIRE(centroid(geom) == geom::geometry_t{geom::point_t{1.1, 2.2}});
     REQUIRE(geometry_n(geom, 1) == geom);
+    REQUIRE(reverse(geom) == geom);
     REQUIRE(geom.get<geom::point_t>() == geom::point_t{1.1, 2.2});
 }
 

tests/test-geom-polygons.cpp

@@ -66,6 +66,15 @@ TEST_CASE("geom::polygon_t", "[NoDB]")
     REQUIRE(area(geom) == Approx(8.0));
     REQUIRE(geometry_type(geom) == "POLYGON");
     REQUIRE(centroid(geom) == geom::geometry_t{geom::point_t{1.5, 1.5}});
+
+    auto const geom_rev = reverse(geom);
+    REQUIRE(geom_rev.is_polygon());
+    auto const &rev = geom_rev.get<geom::polygon_t>();
+    REQUIRE(rev.outer() ==
+            geom::ring_t{{0, 0}, {3, 0}, {3, 3}, {0, 3}, {0, 0}});
+    REQUIRE(rev.inners().size() == 1);
+    REQUIRE(rev.inners()[0] ==
+            geom::ring_t{{1, 1}, {1, 2}, {2, 2}, {2, 1}, {1, 1}});
 }
 
 TEST_CASE("create_polygon from OSM data", "[NoDB]")