Get all OSM trees into JSON using libosmium

get-trees.cpp

// g++ or clang++ -o get-trees get-trees.cpp -O3 -DNDEBUG -I../libosmium/include -std=c++11 -lz -lpthread

#include <exception>
#include <vector>
#include <iostream>
#include <iomanip>

#include <osmium/handler.hpp>
#include <osmium/io/pbf_input.hpp>
#include <osmium/visitor.hpp>

class TreeHandler : public osmium::handler::Handler {
    public:
    TreeHandler() {
    }

    void node(const osmium::Node& node) {
        auto const& tags = node.tags();
        const char * natural_char = tags.get_value_by_key("natural");
        if (natural_char) {
            std::string natural = std::string(natural_char);
            if (!natural.empty() && natural == "tree") {
                auto const& location = node.location();
                if (!first) std::cout << ",";
                std::cout << std::setprecision(8) << "[" << location.lon() << "," << location.lat() << "]";
                first = false;
                trees++;
                std::cerr << trees << "\r";
            }
        }
    }

    private:
    bool first = true;
    uint trees = 0;
};


int main(int argc, char** argv) {
    std::vector<std::string> args;
    for (int i=1;i<argc;++i) {
        args.push_back(argv[i]);
    }

    if (args.empty()) {
        std::clog << "please pass the path to an osm pbf file\n";
        return -1;
    }

    try {
        std::string filename = args[0];
        osmium::io::Reader reader(filename, osmium::osm_entity_bits::node);
        TreeHandler handler;
        std::cout << "[";
        osmium::apply(reader, handler);
        std::cout << "]";
        reader.close();

    } catch (std::exception const& ex) {
        std::clog << "error: " << ex.what() << "\n";
        return -1;
    }
}