text: /*
   * Copyright 2016 The Cartographer Authors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #include "cartographer/mapping/pose_graph_trimmer.h"
  
  #include "glog/logging.h"
  
  namespace cartographer {
  namespace mapping {
  
  PureLocalizationTrimmer::PureLocalizationTrimmer(const int trajectory_id,
                                                   const int num_submaps_to_keep)
      : trajectory_id_(trajectory_id), num_submaps_to_keep_(num_submaps_to_keep) {
    CHECK_GE(num_submaps_to_keep, 2) << "Cannot trim with less than 2 submaps";
  }
  
  // 进行子图的裁剪
  void PureLocalizationTrimmer::Trim(Trimmable* const pose_graph) {
    // 如果轨迹处于完成状态, 就将num_submaps_to_keep_设置为0
    if (pose_graph->IsFinished(trajectory_id_)) {
      num_submaps_to_keep_ = 0;
    }
  
    // 获取所有的SubmapId
    auto submap_ids = pose_graph->GetSubmapIds(trajectory_id_);
    // 从序号0开始裁剪submap, 并删除相关的约束与节点
    for (std::size_t i = 0; i + num_submaps_to_keep_ < submap_ids.size(); ++i) {
      pose_graph->TrimSubmap(submap_ids.at(i));
    }
  
    // 设置轨迹状态为 DELETED
    if (num_submaps_to_keep_ == 0) {
      finished_ = true;
      pose_graph->SetTrajectoryState(
          trajectory_id_, PoseGraphInterface::TrajectoryState::DELETED);
    }
  }
  
  // 获取裁剪器的状态
  bool PureLocalizationTrimmer::IsFinished() { return finished_; }
  
  }  // namespace mapping
  }  // namespace cartographer
  