前言

在Apollo星火计划学习笔记——Apollo路径规划算法原理与实践与【Apollo学习笔记】——Planning模块讲到……Stage::Process的PlanOnReferenceLine函数会依次调用task_list中的TASK，本文将会继续以LaneFollow为例依次介绍其中的TASK部分究竟做了哪些工作。由于个人能力所限，文章可能有纰漏的地方，还请批评斧正。

在modules/planning/conf/scenario/lane_follow_config.pb.txt配置文件中，我们可以看到LaneFollow所需要执行的所有task。

stage_config: {stage_type: LANE_FOLLOW_DEFAULT_STAGEenabled: truetask_type: LANE_CHANGE_DECIDERtask_type: PATH_REUSE_DECIDERtask_type: PATH_LANE_BORROW_DECIDERtask_type: PATH_BOUNDS_DECIDERtask_type: PIECEWISE_JERK_PATH_OPTIMIZERtask_type: PATH_ASSESSMENT_DECIDERtask_type: PATH_DECIDERtask_type: RULE_BASED_STOP_DECIDERtask_type: SPEED_BOUNDS_PRIORI_DECIDERtask_type: SPEED_HEURISTIC_OPTIMIZERtask_type: SPEED_DECIDERtask_type: SPEED_BOUNDS_FINAL_DECIDERtask_type: PIECEWISE_JERK_SPEED_OPTIMIZER# task_type: PIECEWISE_JERK_NONLINEAR_SPEED_OPTIMIZERtask_type: RSS_DECIDER

本文将继续介绍LaneFollow的第6个TASK——PATH_ASSESSMENT_DECIDER

PATH_ASSESSMENT_DECIDER功能简介

路径评价，选出最优路径

由PATH_BOUNDS_DECIDER可以知道会产生以下几种类型的路径边界：

• fallback
• fallback+lanechange
• fallback+pullover
• fallback+regular

依据不同的边界会产生不同的路径，接着便需要筛选出一条最优的路径。依据以下规则，进行评价：

• 路径是否和障碍物碰撞
• 路径长度
• 路径是否会停在对向车道
• 路径离自车远近
• 哪个路径更早回自车道
• …

PATH_ASSESSMENT_DECIDER相关信息

• 输入：Status PathAssessmentDecider::Process(Frame* const frame, ReferenceLineInfo* const reference_line_info)
  输入Frame，reference_line_info。
• 输出：路径排序之后，选择第一个路径。结果保存在reference_line_info中

PATH_ASSESSMENT_DECIDER总体流程

首先来看看PathAssessmentDecider::Process流程部分：

Process部分主要完成路径重复使用判断、去除无效路径、分析路径并加入重要信息提供给速度决策部分、排序选择最优的路径以及最后的更新必要的信息。

1. 去除无效路径

  // 1. Remove invalid path.// 1. 删掉无效路径.std::vector<PathData> valid_path_data;for (const auto& curr_path_data : candidate_path_data) {// RecordDebugInfo(curr_path_data, curr_path_data.path_label(),//                 reference_line_info);if (curr_path_data.path_label().find("fallback") != std::string::npos) {// fallback的无效路径是偏离参考线以及道路的路径if (IsValidFallbackPath(*reference_line_info, curr_path_data)) {valid_path_data.push_back(curr_path_data);}} else {// regular的无效路径是偏离参考线、道路，碰撞，停在相邻的逆向车道的路径。if (IsValidRegularPath(*reference_line_info, curr_path_data)) {valid_path_data.push_back(curr_path_data);}}}const auto& end_time1 = std::chrono::system_clock::now();std::chrono::duration<double> diff = end_time1 - end_time0;ADEBUG << "Time for path validity checking: " << diff.count() * 1000<< " msec.";

其中fallback的无效路径是偏离参考线以及道路的路径。regular的无效路径是偏离参考线、道路，碰撞，停在相邻的逆向车道的路径。

2. 分析并加入重要信息给speed决策

  // 2. Analyze and add important info for speed decider to use// 2. 分析并加入重要信息给speed决策size_t cnt = 0;const Obstacle* blocking_obstacle_on_selflane = nullptr;for (size_t i = 0; i != valid_path_data.size(); ++i) {auto& curr_path_data = valid_path_data[i];if (curr_path_data.path_label().find("fallback") != std::string::npos) {// remove empty path_data.if (!curr_path_data.Empty()) {if (cnt != i) {valid_path_data[cnt] = curr_path_data;}++cnt;}continue;}// 添加相关信息SetPathInfo(*reference_line_info, &curr_path_data);// Trim all the lane-borrowing paths so that it ends with an in-lane// position.// 修剪所有路径（只要不是pull-over），使其能够以in-lane结尾if (curr_path_data.path_label().find("pullover") == std::string::npos) {TrimTailingOutLanePoints(&curr_path_data);}// find blocking_obstacle_on_selflane, to be used for lane selection later// 找到self_lane上的阻塞障碍物, 为下一步选择车道做准备if (curr_path_data.path_label().find("self") != std::string::npos) {const auto blocking_obstacle_id = curr_path_data.blocking_obstacle_id();blocking_obstacle_on_selflane =reference_line_info->path_decision()->Find(blocking_obstacle_id);}// remove empty path_data.if (!curr_path_data.Empty()) {if (cnt != i) {valid_path_data[cnt] = curr_path_data;}++cnt;}// RecordDebugInfo(curr_path_data, curr_path_data.path_label(),//                 reference_line_info);ADEBUG << "For " << curr_path_data.path_label() << ", "<< "path length = " << curr_path_data.frenet_frame_path().size();}valid_path_data.resize(cnt);// If there is no valid path_data, exit.// 如果没有有效路径，退出if (valid_path_data.empty()) {const std::string msg = "Neither regular nor fallback path is valid.";AERROR << msg;return Status(ErrorCode::PLANNING_ERROR, msg);}ADEBUG << "There are " << valid_path_data.size() << " valid path data.";const auto& end_time2 = std::chrono::system_clock::now();diff = end_time2 - end_time1;ADEBUG << "Time for path info labeling: " << diff.count() * 1000 << " msec.";

SetPathInfo

void PathAssessmentDecider::SetPathInfo(const ReferenceLineInfo& reference_line_info, PathData* const path_data) {// Go through every path_point, and label its://  - in-lane/out-of-lane info (side-pass or lane-change)//  - distance to the closest obstacle.std::vector<PathPointDecision> path_decision;// 0. Initialize the path info.InitPathPointDecision(*path_data, &path_decision);// 1. Label caution types, differently for side-pass or lane-change.if (reference_line_info.IsChangeLanePath()) {// If lane-change, then label the lane-changing part to// be out-on-forward lane.SetPathPointType(reference_line_info, *path_data, true, &path_decision);} else {// Otherwise, only do the label for borrow-lane generated paths.// 仅仅对借道进行标记if (path_data->path_label().find("fallback") == std::string::npos &&path_data->path_label().find("self") == std::string::npos) {SetPathPointType(reference_line_info, *path_data, false, &path_decision);}}// SetObstacleDistance(reference_line_info, *path_data, &path_decision);path_data->SetPathPointDecisionGuide(std::move(path_decision));
}

这一部分中函数SetPathInfo完成以下功能：初始化path info；根据是lane-change还是side-pass，设置路径点的类型；添加相关决策引导信息等信息。

SetPathPointType

在设置路径点的类型时涉及到SetPathPointType这一个函数。
流程如下图所示：

void PathAssessmentDecider::SetPathPointType(const ReferenceLineInfo& reference_line_info, const PathData& path_data,const bool is_lane_change_path,std::vector<PathPointDecision>* const path_point_decision) {// Sanity checks.CHECK_NOTNULL(path_point_decision);// Go through every path_point, and add in-lane/out-of-lane info.const auto& discrete_path = path_data.discretized_path();const auto& vehicle_config =common::VehicleConfigHelper::Instance()->GetConfig();const double ego_length = vehicle_config.vehicle_param().length();const double ego_width = vehicle_config.vehicle_param().width();const double ego_back_to_center =vehicle_config.vehicle_param().back_edge_to_center();// 车辆几何中心点与车辆后轴的偏移距离const double ego_center_shift_distance =ego_length / 2.0 - ego_back_to_center;bool is_prev_point_out_lane = false;for (size_t i = 0; i < discrete_path.size(); ++i) {// 以车辆后轴中心获取boundingboxconst auto& rear_center_path_point = discrete_path[i];const double ego_theta = rear_center_path_point.theta();Box2d ego_box({rear_center_path_point.x(), rear_center_path_point.y()},ego_theta, ego_length, ego_width);Vec2d shift_vec{ego_center_shift_distance * std::cos(ego_theta),ego_center_shift_distance * std::sin(ego_theta)};// 将boundingbox从车辆后轴中心变换到几何中心(apollo在这里采用的是AABB的boundingbox，其中有些细节等之后再细看)ego_box.Shift(shift_vec);// 得到SL坐标系下的boundarySLBoundary ego_sl_boundary;if (!reference_line_info.reference_line().GetSLBoundary(ego_box,&ego_sl_boundary)) {ADEBUG << "Unable to get SL-boundary of ego-vehicle.";continue;}double lane_left_width = 0.0;double lane_right_width = 0.0;double middle_s =(ego_sl_boundary.start_s() + ego_sl_boundary.end_s()) / 2.0;if (reference_line_info.reference_line().GetLaneWidth(middle_s, &lane_left_width, &lane_right_width)) {// Rough sl boundary estimate using single point lane widthdouble back_to_inlane_extra_buffer = 0.2;double in_and_out_lane_hysteresis_buffer =is_prev_point_out_lane ? back_to_inlane_extra_buffer : 0.0;// Check for lane-change and lane-borrow differently:if (is_lane_change_path) {// For lane-change path, only transitioning part is labeled as// out-of-lane.if (ego_sl_boundary.start_l() > lane_left_width ||ego_sl_boundary.end_l() < -lane_right_width) {// This means that ADC hasn't started lane-change yet.// 再次重申，变道时是以要变道的目标车道作为参考线std::get<1>((*path_point_decision)[i]) =PathData::PathPointType::IN_LANE;} else if (ego_sl_boundary.start_l() >-lane_right_width + back_to_inlane_extra_buffer &&ego_sl_boundary.end_l() <lane_left_width - back_to_inlane_extra_buffer) {// This means that ADC has safely completed lane-change with margin.std::get<1>((*path_point_decision)[i]) =PathData::PathPointType::IN_LANE;} else {// ADC is right across two lanes.std::get<1>((*path_point_decision)[i]) =PathData::PathPointType::OUT_ON_FORWARD_LANE;}} else {// For lane-borrow path, as long as ADC is not on the lane of// reference-line, it is out on other lanes. It might even be// on reverse lane!if (ego_sl_boundary.end_l() >lane_left_width + in_and_out_lane_hysteresis_buffer ||ego_sl_boundary.start_l() <-lane_right_width - in_and_out_lane_hysteresis_buffer) {if (path_data.path_label().find("reverse") != std::string::npos) {std::get<1>((*path_point_decision)[i]) =PathData::PathPointType::OUT_ON_REVERSE_LANE;} else if (path_data.path_label().find("forward") !=std::string::npos) {std::get<1>((*path_point_decision)[i]) =PathData::PathPointType::OUT_ON_FORWARD_LANE;} else {std::get<1>((*path_point_decision)[i]) =PathData::PathPointType::UNKNOWN;}if (!is_prev_point_out_lane) {if (ego_sl_boundary.end_l() >lane_left_width + back_to_inlane_extra_buffer ||ego_sl_boundary.start_l() <-lane_right_width - back_to_inlane_extra_buffer) {is_prev_point_out_lane = true;}}} else {// The path point is within the reference_line's lane.std::get<1>((*path_point_decision)[i]) =PathData::PathPointType::IN_LANE;if (is_prev_point_out_lane) {is_prev_point_out_lane = false;}}}} else {AERROR << "reference line not ready when setting path point guide";return;}}
}

PS：关于ego_box.Shift(shift_vec);这一步是如何实现的，可以关注这篇博客：Apollo EM中path_assesment_task相关细节的讨论

3. 排序选择最优的路径

  ... ...// 3. Pick the optimal path.// 3. 选择最优路径，两两比较路径。排序是根据 ComparePathData 函数的返回值进行的。std::sort(valid_path_data.begin(), valid_path_data.end(),std::bind(ComparePathData, std::placeholders::_1,std::placeholders::_2, blocking_obstacle_on_selflane));ADEBUG << "Using '" << valid_path_data.front().path_label()<< "' path out of " << valid_path_data.size() << " path(s)";if (valid_path_data.front().path_label().find("fallback") !=std::string::npos) {FLAGS_static_obstacle_nudge_l_buffer = 0.8;}*(reference_line_info->mutable_path_data()) = valid_path_data.front();reference_line_info->SetBlockingObstacle(valid_path_data.front().blocking_obstacle_id());const auto& end_time3 = std::chrono::system_clock::now();diff = end_time3 - end_time2;ADEBUG << "Time for optimal path selection: " << diff.count() * 1000<< " msec.";... ...

主要排序规则在ComparePathData函数中。

bool ComparePathData(const PathData& lhs, const PathData& rhs,const Obstacle* blocking_obstacle) {ADEBUG << "Comparing " << lhs.path_label() << " and " << rhs.path_label();// Empty path_data is never the larger one.// 空的路径永远排在后面if (lhs.Empty()) {ADEBUG << "LHS is empty.";return false;}if (rhs.Empty()) {ADEBUG << "RHS is empty.";return true;}// Regular path goes before fallback path.regular > fallback// 如果lhs是regular路径而rhs是fallback路径，那么lhs会被认为更好，返回true。bool lhs_is_regular = lhs.path_label().find("regular") != std::string::npos;bool rhs_is_regular = rhs.path_label().find("regular") != std::string::npos;if (lhs_is_regular != rhs_is_regular) {return lhs_is_regular;}// Select longer path.// If roughly same length, then select self-lane path.bool lhs_on_selflane = lhs.path_label().find("self") != std::string::npos;bool rhs_on_selflane = rhs.path_label().find("self") != std::string::npos;static constexpr double kSelfPathLengthComparisonTolerance = 15.0;static constexpr double kNeighborPathLengthComparisonTolerance = 25.0;double lhs_path_length = lhs.frenet_frame_path().back().s();double rhs_path_length = rhs.frenet_frame_path().back().s();// 至少其中有一条是self_laneif (lhs_on_selflane || rhs_on_selflane) {// 如果两条路径的长度相差超过了kSelfPathLengthComparisonTolerance（在这里是15.0），那么较长的路径将被认为更好。if (std::fabs(lhs_path_length - rhs_path_length) >kSelfPathLengthComparisonTolerance) {return lhs_path_length > rhs_path_length;} else {// 如果两条路径的长度相差在这个容差范围内，并且其中一条路径在"self"车道上，那么"self"车道上的路径将被认为更好。return lhs_on_selflane;}} else {// 没有一条是self_laneif (std::fabs(lhs_path_length - rhs_path_length) >kNeighborPathLengthComparisonTolerance) {return lhs_path_length > rhs_path_length;}}// If roughly same length, and must borrow neighbor lane,// then prefer to borrow forward lane rather than reverse lane.int lhs_on_reverse =ContainsOutOnReverseLane(lhs.path_point_decision_guide());int rhs_on_reverse =ContainsOutOnReverseLane(rhs.path_point_decision_guide());// TODO(jiacheng): make this a flag.// 如果需要借用逆向车道的次数差超过了6次，那么次数较少的路径将被认为更好（相当于选择逆向距离短的）。if (std::abs(lhs_on_reverse - rhs_on_reverse) > 6) {return lhs_on_reverse < rhs_on_reverse;}// For two lane-borrow directions, based on ADC's position,// select the more convenient one.if ((lhs.path_label().find("left") != std::string::npos &&rhs.path_label().find("right") != std::string::npos) ||(lhs.path_label().find("right") != std::string::npos &&rhs.path_label().find("left") != std::string::npos)) {if (blocking_obstacle) {// select left/right path based on blocking_obstacle's position// 有障碍物，选择合适的方向，左或右借道const double obstacle_l =(blocking_obstacle->PerceptionSLBoundary().start_l() +blocking_obstacle->PerceptionSLBoundary().end_l()) /2;ADEBUG << "obstacle[" << blocking_obstacle->Id() << "] l[" << obstacle_l<< "]";// 如果阻挡障碍物的横向位置大于0（在障碍物的右侧），那么含有"right"的路径将被认为更好；否则，含有"left"的路径将被认为更好。return (obstacle_l > 0.0? (lhs.path_label().find("right") != std::string::npos): (lhs.path_label().find("left") != std::string::npos));} else {// select left/right path based on ADC's position// 无障碍物，根据adc的位置选择借道方向double adc_l = lhs.frenet_frame_path().front().l();if (adc_l < -1.0) {return lhs.path_label().find("right") != std::string::npos;} else if (adc_l > 1.0) {return lhs.path_label().find("left") != std::string::npos;}}}// If same length, both neighbor lane are forward,// then select the one that returns to in-lane earlier.// 路径长度相同，相邻车道都是前向的，选择较早返回自车道的路径static constexpr double kBackToSelfLaneComparisonTolerance = 20.0;int lhs_back_idx = GetBackToInLaneIndex(lhs.path_point_decision_guide());int rhs_back_idx = GetBackToInLaneIndex(rhs.path_point_decision_guide());double lhs_back_s = lhs.frenet_frame_path()[lhs_back_idx].s();double rhs_back_s = rhs.frenet_frame_path()[rhs_back_idx].s();if (std::fabs(lhs_back_s - rhs_back_s) > kBackToSelfLaneComparisonTolerance) {return lhs_back_idx < rhs_back_idx;}// If same length, both forward, back to inlane at same time,// select the left one to side-pass.// 如果路径长度相同，前向借道，返回自车道时间相同，选择从左侧借道的路径bool lhs_on_leftlane = lhs.path_label().find("left") != std::string::npos;bool rhs_on_leftlane = rhs.path_label().find("left") != std::string::npos;if (lhs_on_leftlane != rhs_on_leftlane) {ADEBUG << "Select " << (lhs_on_leftlane ? "left" : "right") << " lane over "<< (!lhs_on_leftlane ? "left" : "right") << " lane.";return lhs_on_leftlane;}// Otherwise, they are the same path, lhs is not < rhs.// 最后如果两条路径相同，则 lhs is not < rhlreturn false;
}

路径排序规则如下：（道路评估的优劣通过排序获得）

1.空的路径永远排在后面
2.regular > fallback
3.如果self-lane有一个存在，选择那个。如果都存在，选择较长的.如果长度接近，选择self-lane如果self-lane都不存在，选择较长的路径
4.如果路径长度接近，且都要借道:

• (1) 都要借逆向车道，选择距离短的
• (2) 针对具有两个借道方向的情况:
  • 有障碍物，选择合适的方向，左或右借道
  • 无障碍物，根据adc的位置选择借道方向
• (3) 路径长度相同，相邻车道都是前向的，选择较早返回自车道的路径
• (4) 如果路径长度相同，前向借道，返回自车道时间相同，选择从左侧借道的路径

5.最后如果两条路径相同，则 lhs is not < rhl

排序之后：选择最优路径，即第一个路径

4. 更新必要的信息

  // 4. Update necessary info for lane-borrow decider's future uses.// Update front static obstacle's info.auto* mutable_path_decider_status = injector_->planning_context()->mutable_planning_status()->mutable_path_decider();if (reference_line_info->GetBlockingObstacle() != nullptr) {int front_static_obstacle_cycle_counter =mutable_path_decider_status->front_static_obstacle_cycle_counter();mutable_path_decider_status->set_front_static_obstacle_cycle_counter(std::max(front_static_obstacle_cycle_counter, 0));mutable_path_decider_status->set_front_static_obstacle_cycle_counter(std::min(front_static_obstacle_cycle_counter + 1, 10));mutable_path_decider_status->set_front_static_obstacle_id(reference_line_info->GetBlockingObstacle()->Id());} else {int front_static_obstacle_cycle_counter =mutable_path_decider_status->front_static_obstacle_cycle_counter();mutable_path_decider_status->set_front_static_obstacle_cycle_counter(std::min(front_static_obstacle_cycle_counter, 0));mutable_path_decider_status->set_front_static_obstacle_cycle_counter(std::max(front_static_obstacle_cycle_counter - 1, -10));}// Update self-lane usage info.if (reference_line_info->path_data().path_label().find("self") !=std::string::npos) {// && std::get<1>(reference_line_info->path_data()//                 .path_point_decision_guide()//                 .front()) == PathData::PathPointType::IN_LANE)int able_to_use_self_lane_counter =mutable_path_decider_status->able_to_use_self_lane_counter();if (able_to_use_self_lane_counter < 0) {able_to_use_self_lane_counter = 0;}mutable_path_decider_status->set_able_to_use_self_lane_counter(std::min(able_to_use_self_lane_counter + 1, 10));} else {mutable_path_decider_status->set_able_to_use_self_lane_counter(0);}// Update side-pass direction.if (mutable_path_decider_status->is_in_path_lane_borrow_scenario()) {bool left_borrow = false;bool right_borrow = false;const auto& path_decider_status =injector_->planning_context()->planning_status().path_decider();for (const auto& lane_borrow_direction :path_decider_status.decided_side_pass_direction()) {if (lane_borrow_direction == PathDeciderStatus::LEFT_BORROW &&reference_line_info->path_data().path_label().find("left") !=std::string::npos) {left_borrow = true;}if (lane_borrow_direction == PathDeciderStatus::RIGHT_BORROW &&reference_line_info->path_data().path_label().find("right") !=std::string::npos) {right_borrow = true;}}mutable_path_decider_status->clear_decided_side_pass_direction();if (right_borrow) {mutable_path_decider_status->add_decided_side_pass_direction(PathDeciderStatus::RIGHT_BORROW);}if (left_borrow) {mutable_path_decider_status->add_decided_side_pass_direction(PathDeciderStatus::LEFT_BORROW);}}const auto& end_time4 = std::chrono::system_clock::now();diff = end_time4 - end_time3;ADEBUG << "Time for FSM state updating: " << diff.count() * 1000 << " msec.";// Plot the path in simulator for debug purpose.RecordDebugInfo(reference_line_info->path_data(), "Planning PathData",reference_line_info);return Status::OK();

更新必要信息：

1.更新adc前方静态障碍物的信息
2.更新自车道使用信息
3.更新旁车道的方向根据：PathDeciderStatus是RIGHT_BORROW或LEFT_BORROW判断是从左侧借道，还是从右侧借道