VINS-Mono LoopClosure

[TOC]

Overview

• 忽略掉了 shift to base frame：w_t_vio, w_r_vio

loop closure 初始化

• PoseGraph 设置
  • 设置参数
  • 启动线程 PoseGraph::optimize4DoF 或 PoseGraph::optimize6DoF
  • 加载 词典文件
• 启动线程 SystemROS::loop_closing

线程 loop_closing

• 获取同步的图像、位姿、2D与3D点信息
  • img
  • pose
  • point_id, point_3d, point_2d_uv, point_2d_normal
• 构建 KeyFrame
  • KeyFrame 成员变量初始化
  • computeWindowBRIEFPoint: 根据 point_2d_uv 生成 window_keypoints， 计算其对应的描述子 window_brief_descriptors
  • computeBRIEFPoint: 提取 FAST 特征点，一起和 point_2d_uv 放到 keypoints，计算其描述子 brief_descriptors 和 keypoints_norm
• addKeyFrame
  • cur_kf->index = global_index++;
  • loop_index = detectLoop(cur_kf, cur_kf->index)
    • db.query(keyframe->brief_descriptors, ret, 3, max_frame_id_allowed)
    • db.add(keyframe->brief_descriptors);
  • KeyFrame* old_kf = getKeyFrame(loop_index)
  • cur_kf->findConnection(old_kf)
    • point_2d_uv --> point_2d_norm
    • old_kf->keypoints --> old_kf->keypoints_norm
    • searchByBRIEFDes: window_brief_descriptors <--> old_kf->brief_descriptors --> matched_2d_old_norm
    • PnP RANSAC (利用PnP得到回环帧位姿): matched_3d <--> matched_2d_old_norm --> PnP_T_old, PnP_R_old
    • get loop_info (计算PnP得到的回环帧的位姿与当前帧位姿的相对变换): relative_t, relative_q, relative_yaw
  • earliest_loop_index = loop_index;
  • optimize_buf: optimize_buf.push(cur_kf->index);
  • updatePose

    cur_kf->getVioPose(P, R);
    P = r_drift * P + t_drift;
    R = r_drift * R;
    cur_kf->updatePose(P, R);

  • keyframelist: keyframelist.push_back(cur_kf);

线程 optimize4DoF

• get first_looped_index and cur_index

  while (!optimize_buf.empty()) {
      cur_index = optimize_buf.front();
      first_looped_index = earliest_loop_index;
      optimize_buf.pop();
  }

• ceres solver 优化
  • 遍历 keyframelist， 忽略 first_looped_index 之前的 keyframe，直到 cur_index
  • getVioPose --> t_array, q_array, euler_array
  • problem.AddParameterBlock: euler_array, t_array
  • problem.SetParameterBlockConstant: first_looped_index
  • problem.AddResidualBlock
    • 相邻帧约束关系
    • 回环边和顶点
  • ceres::Solve(options, &problem, &summary);
• updatePose
  • 遍历 keyframelist， 忽略 first_looped_index 之前的 keyframe，直到 cur_index
  • updatePose: euler_array, t_array

• get drift: yaw_drift, r_drift, t_drift \[ T_{drift} = T_{opt} * T_{vio}^{-1} \]

• updatePose
  • 遍历 cur_index 之后的 keyframelist
  • updatePose

    (it)->getVioPose(P, R);
    P = r_drift * P + t_drift;
    R = r_drift * R;
    (it)->updatePose(P, R);

• updatePath
  • 遍历 keyframelist，获取位姿 getPose 给 Path

线程 optimize6DoF

FAST_RELOCALIZATION

• cur_kf->findConnection(old_kf)
  • publish: 回环帧的 matched_2d_old_norm, matched_id, T_wi
• relocalization_callback
  • subscribe: get relo_buf
• process loop
  • get latest relo_msg from relo_buf
  • estimator.setReloFrame(frame_stamp, frame_index, match_points, relo_t, relo_r);
    • relo_frame_index
    • match_points
    • prev_relo_t
    • prev_relo_r
    • relo_Pose <-- para_Pose
    • relo_frame_local_index <-- i
    • relocalization_info = 1
• optimization
  • problem.AddParameterBlock: relo_Pose
  • problem.AddResidualBlock
• double2vector(?????)
  • drift_correct_r, drift_correct_t
  • relo_relative_q, relo_relative_t, relo_relative_yaw
• publish
  • pub_relo_path
    • drift_correct_r, drift_correct_t + estimator.Ps[WINDOW_SIZE] --> correct_t, correct_q
  • pub_relo_relative_pose (relo_relative_pose)
    • relo_relative_q, relo_relative_t, relo_relative_yaw
• relo_relative_pose_callback
  • loop_info <-- relo_relative_pose
  • posegraph.updateKeyFrameLoop(index, loop_info);
    • get drift: yaw_drift, r_drift, t_drift