Cache reprojection objects in flex output

Author: joto

src/flex-lua-geom.cpp

@@ -223,10 +223,8 @@ static int geom_transform(lua_State *lua_state)
             throw std::runtime_error{
                 "Can not transform already transformed geometry."};
         }
-        auto const proj = reprojection::create_projection(srid);
-
         auto *geom = create_lua_geometry_object(lua_state);
-        geom::transform(geom, *input_geometry, *proj);
+        geom::transform(geom, *input_geometry, get_projection(srid));
     } catch (...) {
         return luaL_error(lua_state, "Unknown error in 'transform()'.\n");
     }

src/flex-write.cpp

@@ -473,9 +473,8 @@ void flex_write_column(lua_State *lua_state,
                     expire->from_geometry_if_3857(*geom);
                     copy_mgr->add_hex_geom(geom_to_ewkb(*geom, wrap_multi));
                 } else {
-                    auto const proj =
-                        reprojection::create_projection(column.srid());
-                    auto const tgeom = geom::transform(*geom, *proj);
+                    auto const &proj = get_projection(column.srid());
+                    auto const tgeom = geom::transform(*geom, proj);
                     expire->from_geometry_if_3857(tgeom);
                     copy_mgr->add_hex_geom(geom_to_ewkb(tgeom, wrap_multi));
                 }
@@ -512,8 +511,7 @@ void flex_write_row(lua_State *lua_state, table_connection_t *table_connection,
     geom::geometry_t projected_geom;
     geom::geometry_t const *output_geom = &geom;
     if (srid && geom.srid() != srid) {
-        auto const proj = reprojection::create_projection(srid);
-        projected_geom = geom::transform(geom, *proj);
+        projected_geom = geom::transform(geom, get_projection(srid));
         output_geom = &projected_geom;
     }
 
@@ -543,11 +541,8 @@ void flex_write_row(lua_State *lua_state, table_connection_t *table_connection,
                 } else if (column.srid() == srid) {
                     area = geom::area(projected_geom);
                 } else {
-                    // XXX there is some overhead here always dynamically
-                    // creating the same projection object. Needs refactoring.
-                    auto const mproj =
-                        reprojection::create_projection(column.srid());
-                    area = geom::area(geom::transform(geom, *mproj));
+                    auto const &mproj = get_projection(column.srid());
+                    area = geom::area(geom::transform(geom, mproj));
                 }
                 copy_mgr->add_column(area);
             }

src/reprojection.cpp

@@ -86,3 +86,18 @@ std::shared_ptr<reprojection> reprojection::create_projection(int srs)
 
     return make_generic_projection(srs);
 }
+
+reprojection const &get_projection(int srs)
+{
+    // In almost all cases there will be only one or two projections used, so
+    // storing them in a vector and doing linear search is totally fine.
+    static std::vector<std::shared_ptr<reprojection>> projections;
+
+    for (auto const &p : projections) {
+        if (p->target_srs() == srs) {
+            return *p;
+        }
+    }
+
+    return *projections.emplace_back(reprojection::create_projection(srs));
+}

src/reprojection.hpp

@@ -71,4 +71,10 @@ class reprojection
 
 std::string get_proj_version();
 
+/**
+ * Get projection object for given srs. Objects are only created once and
+ * then cached.
+ */
+reprojection const &get_projection(int srs);
+
 #endif // OSM2PGSQL_REPROJECTION_HPP