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EXAMPLE osmium_area_test
Create multipolygons from OSM data and dump them to stdout in one of two
formats: WKT or using the built-in Dump format.
* file input
* location indexes and the NodeLocationsForWays handler
* the MultipolygonManager and Assembler to assemble areas (multipolygons)
* your own handler that works with areas (multipolygons)
* the WKTFactory to write geometries in WKT format
* the Dump handler
* the DynamicHandler
SIMPLER EXAMPLES you might want to understand first:
* osmium_read
* osmium_count
* osmium_debug
* osmium_amenity_list
The code in this example file is released into the Public Domain.
#include <cstdlib> // for std::exit
#include <cstring> // for std::strcmp
#include <iostream> // for std::cout, std::cerr
// For assembling multipolygons
#include <osmium/area/assembler.hpp>
#include <osmium/area/multipolygon_manager.hpp>
// For the DynamicHandler class
#include <osmium/dynamic_handler.hpp>
// For the WKT factory
#include <osmium/geom/wkt.hpp>
// For the Dump handler
#include <osmium/handler/dump.hpp>
// For the NodeLocationForWays handler
#include <osmium/handler/node_locations_for_ways.hpp>
// Allow any format of input files (XML, PBF, ...)
#include <osmium/io/any_input.hpp>
// For osmium::apply()
#include <osmium/visitor.hpp>
// For the location index. There are different types of indexes available.
// This will work for all input files keeping the index in memory.
#include <osmium/index/map/flex_mem.hpp>
// The type of index used. This must match the include file above
using index_type = osmium::index::map::FlexMem<osmium::unsigned_object_id_type, osmium::Location>;
// The location handler always depends on the index type
using location_handler_type = osmium::handler::NodeLocationsForWays<index_type>;
// This handler writes all area geometries out in WKT (Well Known Text) format.
class WKTDump : public osmium::handler::Handler {
// This factory is used to create a geometry in WKT format from OSM
// objects. The template parameter is empty here, because we output WGS84
// coordinates, but could be used for a projection.
osmium::geom::WKTFactory<> m_factory;
// This callback is called by osmium::apply for each area in the data.
void area(const osmium::Area& area) {
try {
std::cout << m_factory.create_multipolygon(area) << "\n";
} catch (const osmium::geometry_error& e) {
std::cout << "GEOMETRY ERROR: " << e.what() << "\n";
}; // class WKTDump
void print_help() {
std::cout << "osmium_area_test [OPTIONS] OSMFILE\n\n"
<< "Read OSMFILE and build multipolygons from it.\n"
<< "\nOptions:\n"
<< " -h, --help This help message\n"
<< " -w, --dump-wkt Dump area geometries as WKT\n"
<< " -o, --dump-objects Dump area objects\n";
void print_usage(const char* prgname) {
std::cerr << "Usage: " << prgname << " [OPTIONS] OSMFILE\n";
int main(int argc, char* argv[]) {
if (argc > 1 && (!std::strcmp(argv[1], "-h") ||
!std::strcmp(argv[1], "--help"))) {
if (argc != 3) {
// Initialize an empty DynamicHandler. Later it will be associated
// with one of the handlers. You can think of the DynamicHandler as
// a kind of "variant handler" or a "pointer handler" pointing to the
// real handler.
osmium::handler::DynamicHandler handler;
if (!std::strcmp(argv[1], "-w") || !std::strcmp(argv[1], "--dump-wkt")) {
} else if (!std::strcmp(argv[1], "-o") || !std::strcmp(argv[1], "--dump-objects")) {
} else {
osmium::io::File input_file{argv[2]};
// Configuration for the multipolygon assembler. Here the default settings
// are used, but you could change multiple settings.
osmium::area::Assembler::config_type assembler_config;
// Set up a filter matching only forests. This will be used to only build
// areas with matching tags.
osmium::TagsFilter filter{false};
filter.add_rule(true, "landuse", "forest");
filter.add_rule(true, "natural", "wood");
// Initialize the MultipolygonManager. Its job is to collect all
// relations and member ways needed for each area. It then calls an
// instance of the osmium::area::Assembler class (with the given config)
// to actually assemble one area. The filter parameter is optional, if
// it is not set, all areas will be built.
osmium::area::MultipolygonManager<osmium::area::Assembler> mp_manager{assembler_config, filter};
// We read the input file twice. In the first pass, only relations are
// read and fed into the multipolygon manager.
std::cerr << "Pass 1...\n";
osmium::relations::read_relations(input_file, mp_manager);
std::cerr << "Pass 1 done\n";
// Output the amount of main memory used so far. All multipolygon relations
// are in memory now.
std::cerr << "Memory:\n";
osmium::relations::print_used_memory(std::cerr, mp_manager.used_memory());
// The index storing all node locations.
index_type index;
// The handler that stores all node locations in the index and adds them
// to the ways.
location_handler_type location_handler{index};
// If a location is not available in the index, we ignore it. It might
// not be needed (if it is not part of a multipolygon relation), so why
// create an error?
// On the second pass we read all objects and run them first through the
// node location handler and then the multipolygon collector. The collector
// will put the areas it has created into the "buffer" which are then
// fed through our "handler".
std::cerr << "Pass 2...\n";
osmium::io::Reader reader{input_file};
osmium::apply(reader, location_handler, mp_manager.handler([&handler](osmium::memory::Buffer&& buffer) {
osmium::apply(buffer, handler);
std::cerr << "Pass 2 done\n";
// Output the amount of main memory used so far. All complete multipolygon
// relations have been cleaned up.
std::cerr << "Memory:\n";
osmium::relations::print_used_memory(std::cerr, mp_manager.used_memory());
// If there were multipolgyon relations in the input, but some of their
// members are not in the input file (which often happens for extracts)
// this will write the IDs of the incomplete relations to stderr.
std::vector<osmium::object_id_type> incomplete_relations_ids;
mp_manager.for_each_incomplete_relation([&](const osmium::relations::RelationHandle& handle){
if (!incomplete_relations_ids.empty()) {
std::cerr << "Warning! Some member ways missing for these multipolygon relations:";
for (const auto id : incomplete_relations_ids) {
std::cerr << " " << id;
std::cerr << "\n";