geojson文件示例，

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates": [102.0, 0.5]
      },
      "properties": {
        "name": "Example Point"
      }
    },
    {
      "type": "Feature",
      "geometry": {
        "type": "LineString",
        "coordinates": [
          [102.0, 0.0],
          [103.0, 1.0],
          [104.0, 0.0],
          [105.0, 1.0]
        ]
      },
      "properties": {
        "name": "Example Line"
      }
    },
    {
      "type": "Feature",
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [100.0, 0.0],
            [101.0, 0.0],
            [101.0, 1.0],
            [100.0, 1.0],
            [100.0, 0.0]
          ]
        ]
      },
      "properties": {
        "name": "Example Polygon"
      }
    }
  ]
}

生成geojson文件的C++代码示例，

void GlobalMappingImpl::generate_geojson_gnss() const {
    Json::Value root;
    root.clear();
    root["type"] = "FeatureCollection";
    root["name"] = "SingleTrajectoryGlobalRes";
    auto& root_features = root["features"];

    auto _it_meas = _map_gnss._meas_map.begin();
    while (_map_gnss._meas_map.size() >= 1 && _it_meas != _map_gnss._meas_map.end()) {
        Json::Value json;
        json["type"] = "Feature";
        auto& json_properties = json["properties"];
        json_properties["name"] = "GNSS";
        json_properties["head_veh"].append(_it_meas->second->head_veh());
        json_properties["fix_type"].append(_it_meas->second->fix_type());
        auto& json_geometry = json["geometry"];
        json_geometry["type"] = "Point";
        json_geometry["coordinates"].append(_it_meas->second->lon());
        json_geometry["coordinates"].append(_it_meas->second->lat());
        root_features.append(json);
        _it_meas++;
    }
    static Json::FastWriter fast_write;
    auto* file = new std::ofstream("./debug_optimized_gnss.geojson", std::ios::trunc);
    if (file->is_open()) {
        *file << fast_write.write(root);
        file->flush();
        file->close();
    }
    delete file;
}