本次阅读的源码为 release-1.0 版本的代码

https://github.com/googlecartographer/cartographer_ros/tree/release-1.0

https://github.com/googlecartographer/cartographer/tree/release-1.0

也可以下载我上传的 全套工作空间的代码，包括 protobuf, cartographer, cartographer_ros, ceres,

https://download.csdn.net/download/tiancailx/11224156

cartographer/mapping/internal/2d/pose_graph_2d.cc

AddImuData()

首先通过　global_trajectory_builder.cc　调用　pose_graph_2d.cc　的　AddImuData(), AddOdometryData()

// cartographer/mapping/internal/optimization/optimization_problem_2d.cc
void PoseGraph2D::AddImuData(const int trajectory_id,
                             const sensor::ImuData& imu_data) {
  common::MutexLocker locker(&mutex_);
  AddWorkItem([=]() REQUIRES(mutex_) {
    optimization_problem_->AddImuData(trajectory_id, imu_data);
  });
}
 
void PoseGraph2D::AddOdometryData(const int trajectory_id,
                                  const sensor::OdometryData& odometry_data) {
  common::MutexLocker locker(&mutex_);
  AddWorkItem([=]() REQUIRES(mutex_) {
    optimization_problem_->AddOdometryData(trajectory_id, odometry_data);
  });
}

AddTrajectoryNode()

再通过　global_trajectory_builder.cc　调用　pose_graph_2d.cc　的　AddNode()  --> ComputeConstraintsForNode() --> optimization_problem_->AddTrajectoryNode()

void PoseGraph2D::ComputeConstraintsForNode(
    const NodeId& node_id,
    std::vector<std::shared_ptr<const Submap2D>> insertion_submaps,
    const bool newly_finished_submap) {
 
 
  optimization_problem_->AddTrajectoryNode(
      matching_id.trajectory_id,
      optimization::NodeSpec2D{constant_data->time, local_pose_2d,
                               global_pose_2d,
                               constant_data->gravity_alignment});
 
}

AddSubmap()

ComputeConstraintsForNode()  --> ComputeConstraint() --> 

std::vector<SubmapId> PoseGraph2D::InitializeGlobalSubmapPoses(
    const int trajectory_id, const common::Time time,
    const std::vector<std::shared_ptr<const Submap2D>>& insertion_submaps) {
  CHECK(!insertion_submaps.empty());
  const auto& submap_data = optimization_problem_->submap_data();
  if (insertion_submaps.size() == 1) {
    // If we don't already have an entry for the first submap, add one.
    if (submap_data.SizeOfTrajectoryOrZero(trajectory_id) == 0) {
      if (initial_trajectory_poses_.count(trajectory_id) > 0) {
        trajectory_connectivity_state_.Connect(
            trajectory_id,
            initial_trajectory_poses_.at(trajectory_id).to_trajectory_id, time);
      }
 
      optimization_problem_->AddSubmap(
          trajectory_id,
          transform::Project2D(ComputeLocalToGlobalTransform(
                                   global_submap_poses_, trajectory_id) *
                               insertion_submaps[0]->local_pose()));
 
    }
    CHECK_EQ(1, submap_data.SizeOfTrajectoryOrZero(trajectory_id));
    const SubmapId submap_id{trajectory_id, 0};
    CHECK(submap_data_.at(submap_id).submap == insertion_submaps.front());
    return {submap_id};
  }
  CHECK_EQ(2, insertion_submaps.size());
  const auto end_it = submap_data.EndOfTrajectory(trajectory_id);
  CHECK(submap_data.BeginOfTrajectory(trajectory_id) != end_it);
  const SubmapId last_submap_id = std::prev(end_it)->id;
  if (submap_data_.at(last_submap_id).submap == insertion_submaps.front()) {
    // In this case, 'last_submap_id' is the ID of
    // 'insertions_submaps.front()' and 'insertions_submaps.back()' is new.
    const auto& first_submap_pose = submap_data.at(last_submap_id).global_pose;
 
    optimization_problem_->AddSubmap(
        trajectory_id,
        first_submap_pose *
            constraints::ComputeSubmapPose(*insertion_submaps[0]).inverse() *
            constraints::ComputeSubmapPose(*insertion_submaps[1]));
 
    return {last_submap_id,
            SubmapId{trajectory_id, last_submap_id.submap_index + 1}};
  }
  CHECK(submap_data_.at(last_submap_id).submap == insertion_submaps.back());
  const SubmapId front_submap_id{trajectory_id,
                                 last_submap_id.submap_index - 1};
  CHECK(submap_data_.at(front_submap_id).submap == insertion_submaps.front());
  return {front_submap_id, last_submap_id};
}

Solve()

ComputeConstraintsForNode()  --> DispatchOptimization() --> HandleWorkQueue() --> RunOptimization() --> 

optimization_problem_->Solve()

void PoseGraph2D::DispatchOptimization() {
  run_loop_closure_ = true;
  // If there is a 'work_queue_' already, some other thread will take care.
  if (work_queue_ == nullptr) {
    work_queue_ = common::make_unique<std::deque<std::function<void()>>>();
    constraint_builder_.WhenDone(
        std::bind(&PoseGraph2D::HandleWorkQueue, this, std::placeholders::_1));
  }
}
 
void PoseGraph2D::HandleWorkQueue(
    const constraints::ConstraintBuilder2D::Result& result) {
  {
    common::MutexLocker locker(&mutex_);
    constraints_.insert(constraints_.end(), result.begin(), result.end());
  }
  RunOptimization();
 
  // ...
 
}
 
void PoseGraph2D::RunOptimization() {
  if (optimization_problem_->submap_data().empty()) {
    return;
  }
 
  // No other thread is accessing the optimization_problem_, constraints_,
  // frozen_trajectories_ and landmark_nodes_ when executing the Solve. Solve is
  // time consuming, so not taking the mutex before Solve to avoid blocking
  // foreground processing.
  optimization_problem_->Solve(constraints_, frozen_trajectories_,
                               landmark_nodes_);
  // ...
}

cartographer/mapping/internal/optimization/optimization_problem_2d.cc

struct NodeSpec2D {
  common::Time time;
  transform::Rigid2d local_pose_2d;
  transform::Rigid2d global_pose_2d;
  Eigen::Quaterniond gravity_alignment;
};
 
struct SubmapSpec2D {
  transform::Rigid2d global_pose;
};

void OptimizationProblem2D::Solve(
    const std::vector<Constraint>& constraints,
    const std::set<int>& frozen_trajectories,
    const std::map<std::string, LandmarkNode>& landmark_nodes) {
  if (node_data_.empty()) {
    // Nothing to optimize.
    return;
  }
 
  ceres::Problem::Options problem_options;
  ceres::Problem problem(problem_options);
 
  // Set the starting point.
  // TODO(hrapp): Move ceres data into SubmapSpec.
  MapById<SubmapId, std::array<double, 3>> C_submaps;
  MapById<NodeId, std::array<double, 3>> C_nodes;
  std::map<std::string, CeresPose> C_landmarks;
  bool first_submap = true;
  bool freeze_landmarks = !frozen_trajectories.empty();
  for (const auto& submap_id_data : submap_data_) {
    const bool frozen =
        frozen_trajectories.count(submap_id_data.id.trajectory_id) != 0;
    C_submaps.Insert(submap_id_data.id,
                     FromPose(submap_id_data.data.global_pose));
    problem.AddParameterBlock(C_submaps.at(submap_id_data.id).data(), 3);
    if (first_submap || frozen) {
      first_submap = false;
      // Fix the pose of the first submap or all submaps of a frozen
      // trajectory.
      problem.SetParameterBlockConstant(C_submaps.at(submap_id_data.id).data());
    }
  }
  for (const auto& node_id_data : node_data_) {
    const bool frozen =
        frozen_trajectories.count(node_id_data.id.trajectory_id) != 0;
    C_nodes.Insert(node_id_data.id, FromPose(node_id_data.data.global_pose_2d));
    problem.AddParameterBlock(C_nodes.at(node_id_data.id).data(), 3);
    if (frozen) {
      problem.SetParameterBlockConstant(C_nodes.at(node_id_data.id).data());
    }
  }
  // Add cost functions for intra- and inter-submap constraints.
  for (const Constraint& constraint : constraints) {
    problem.AddResidualBlock(
        CreateAutoDiffSpaCostFunction(constraint.pose),
        // Only loop closure constraints should have a loss function.
        constraint.tag == Constraint::INTER_SUBMAP
            ? new ceres::HuberLoss(options_.huber_scale())
            : nullptr,
        C_submaps.at(constraint.submap_id).data(),
        C_nodes.at(constraint.node_id).data());
  }
  // Add cost functions for landmarks.
  AddLandmarkCostFunctions(landmark_nodes, freeze_landmarks, node_data_,
                           &C_nodes, &C_landmarks, &problem);
  // Add penalties for violating odometry or changes between consecutive nodes
  // if odometry is not available.
  for (auto node_it = node_data_.begin(); node_it != node_data_.end();) {
    const int trajectory_id = node_it->id.trajectory_id;
    const auto trajectory_end = node_data_.EndOfTrajectory(trajectory_id);
    if (frozen_trajectories.count(trajectory_id) != 0) {
      node_it = trajectory_end;
      continue;
    }
 
    auto prev_node_it = node_it;
    for (++node_it; node_it != trajectory_end; ++node_it) {
      const NodeId first_node_id = prev_node_it->id;
      const NodeSpec2D& first_node_data = prev_node_it->data;
      prev_node_it = node_it;
      const NodeId second_node_id = node_it->id;
      const NodeSpec2D& second_node_data = node_it->data;
 
      if (second_node_id.node_index != first_node_id.node_index + 1) {
        continue;
      }
 
      // Add a relative pose constraint based on the odometry (if available).
      std::unique_ptr<transform::Rigid3d> relative_odometry =
          CalculateOdometryBetweenNodes(trajectory_id, first_node_data,
                                        second_node_data);
      if (relative_odometry != nullptr) {
        problem.AddResidualBlock(
            CreateAutoDiffSpaCostFunction(Constraint::Pose{
                *relative_odometry, options_.odometry_translation_weight(),
                options_.odometry_rotation_weight()}),
            nullptr /* loss function */, C_nodes.at(first_node_id).data(),
            C_nodes.at(second_node_id).data());
      }
 
      // Add a relative pose constraint based on consecutive local SLAM poses.
      const transform::Rigid3d relative_local_slam_pose =
          transform::Embed3D(first_node_data.local_pose_2d.inverse() *
                             second_node_data.local_pose_2d);
      problem.AddResidualBlock(
          CreateAutoDiffSpaCostFunction(
              Constraint::Pose{relative_local_slam_pose,
                               options_.local_slam_pose_translation_weight(),
                               options_.local_slam_pose_rotation_weight()}),
          nullptr /* loss function */, C_nodes.at(first_node_id).data(),
          C_nodes.at(second_node_id).data());
    }
  }
 
  // Solve.
  ceres::Solver::Summary summary;
  ceres::Solve(
      common::CreateCeresSolverOptions(options_.ceres_solver_options()),
      &problem, &summary);
  if (options_.log_solver_summary()) {
    LOG(INFO) << summary.FullReport();
  }
 
  // Store the result.
  for (const auto& C_submap_id_data : C_submaps) {
    submap_data_.at(C_submap_id_data.id).global_pose =
        ToPose(C_submap_id_data.data);
  }
  for (const auto& C_node_id_data : C_nodes) {
    node_data_.at(C_node_id_data.id).global_pose_2d =
        ToPose(C_node_id_data.data);
  }
  for (const auto& C_landmark : C_landmarks) {
    landmark_data_[C_landmark.first] = C_landmark.second.ToRigid();
  }
}

CostFunction

ceres::CostFunction* CreateAutoDiffSpaCostFunction(
    const PoseGraphInterface::Constraint::Pose& observed_relative_pose) {
  return new ceres::AutoDiffCostFunction<SpaCostFunction2D, 3 /* residuals */,
                                         3 /* start pose variables */,
                                         3 /* end pose variables */>(
      new SpaCostFunction2D(observed_relative_pose));
}
 
class SpaCostFunction2D {
 public:
  explicit SpaCostFunction2D(
      const PoseGraphInterface::Constraint::Pose& observed_relative_pose)
      : observed_relative_pose_(observed_relative_pose) {}
 
  template <typename T>
  bool operator()(const T* const start_pose, const T* const end_pose,
                  T* e) const {
    const std::array<T, 3> error =
        ScaleError(ComputeUnscaledError(
                       transform::Project2D(observed_relative_pose_.zbar_ij),
                       start_pose, end_pose),
                   observed_relative_pose_.translation_weight,
                   observed_relative_pose_.rotation_weight);
    std::copy(std::begin(error), std::end(error), e);
    return true;
  }
 
 private:
  const PoseGraphInterface::Constraint::Pose observed_relative_pose_;
};

references

1 https://blog.csdn.net/xiaoma_bk/article/details/82392295 --- cartographer 子图和节点的优化

2 https://blog.csdn.net/MyArrow/article/details/82909148 --- Cartographer SPA残差

3