From 503785a387de5604ccc102936e8e521c06afb3e5 Mon Sep 17 00:00:00 2001
From: panjiacheng <panjiacheng@yahoo.com>
Date: Wed, 17 Jul 2019 15:14:40 -0700
Subject: [PATCH] Prediction: add some comments and fix some minor bugs.

---
 modules/prediction/common/junction_analyzer.cc       | 12 +++++++++++-
 modules/prediction/container/obstacles/obstacle.cc   |  8 ++++++++
 .../scripts/records_to_data_for_learning.sh          |  1 -
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/modules/prediction/common/junction_analyzer.cc b/modules/prediction/common/junction_analyzer.cc
index ffec40182b..a739187608 100644
--- a/modules/prediction/common/junction_analyzer.cc
+++ b/modules/prediction/common/junction_analyzer.cc
@@ -32,7 +32,9 @@ using apollo::hdmap::LaneInfo;
 using ConstLaneInfoPtr = std::shared_ptr<const LaneInfo>;
 
 std::shared_ptr<const JunctionInfo> JunctionAnalyzer::junction_info_ptr_;
+// Maps exit lane-id to JunctionExit info.
 std::unordered_map<std::string, JunctionExit> JunctionAnalyzer::junction_exits_;
+// Maps starting lane-id to JunctionFeature info.
 std::unordered_map<std::string, JunctionFeature>
     JunctionAnalyzer::junction_features_;
 
@@ -55,11 +57,14 @@ void JunctionAnalyzer::Clear() {
 
 void JunctionAnalyzer::SetAllJunctionExits() {
   CHECK_NOTNULL(junction_info_ptr_);
+  // Go through everything that the junction overlaps with.
   for (const auto& overlap_id : junction_info_ptr_->junction().overlap_id()) {
     auto overlap_info_ptr = PredictionMap::OverlapById(overlap_id.id());
     if (overlap_info_ptr == nullptr) {
       continue;
     }
+    // Find the lane-segments that are overlapping, yet also extends out of
+    // the junction area. Those are the junction-exit-lanes.
     for (const auto& object : overlap_info_ptr->overlap().object()) {
       if (object.has_lane_overlap_info()) {
         const std::string& lane_id = object.id().id();
@@ -90,18 +95,22 @@ std::vector<JunctionExit> JunctionAnalyzer::GetJunctionExits(
   std::vector<JunctionExit> junction_exits;
   std::queue<std::pair<ConstLaneInfoPtr, int>> lane_info_queue;
   lane_info_queue.emplace(PredictionMap::LaneById(start_lane_id), 0);
+  std::unordered_set<std::string> visited_exit_lanes;
+  // Perform a BFS to find all exit lanes that can be connected through
+  // this start_lane_id.
   while (!lane_info_queue.empty()) {
     ConstLaneInfoPtr curr_lane = lane_info_queue.front().first;
     int level = lane_info_queue.front().second;
     lane_info_queue.pop();
     const std::string& curr_lane_id = curr_lane->id().id();
-    std::unordered_set<std::string> visited_exit_lanes;
+    // Stop if this is already an exit lane.
     if (IsExitLane(curr_lane_id) &&
         visited_exit_lanes.find(curr_lane_id) == visited_exit_lanes.end()) {
       junction_exits.push_back(junction_exits_[curr_lane_id]);
       visited_exit_lanes.insert(curr_lane_id);
       continue;
     }
+    // Stop if reached max-search-level.
     if (level >= max_search_level) {
       continue;
     }
@@ -122,6 +131,7 @@ const JunctionFeature& JunctionAnalyzer::GetJunctionFeature(
   JunctionFeature junction_feature;
   junction_feature.set_junction_id(GetJunctionId());
   junction_feature.set_junction_range(ComputeJunctionRange());
+  // Find all junction-exit-lanes that are successors of the start_lane_id.
   std::vector<JunctionExit> junction_exits = GetJunctionExits(start_lane_id);
 
   for (const auto& junction_exit : junction_exits) {
diff --git a/modules/prediction/container/obstacles/obstacle.cc b/modules/prediction/container/obstacles/obstacle.cc
index 39c98f2f82..6c9eb8de95 100644
--- a/modules/prediction/container/obstacles/obstacle.cc
+++ b/modules/prediction/container/obstacles/obstacle.cc
@@ -237,16 +237,20 @@ bool Obstacle::IsInJunction(const std::string& junction_id) const {
 }
 
 void Obstacle::BuildJunctionFeature() {
+  // If obstacle has no history at all, then exit.
   if (feature_history_.empty()) {
     AERROR << "Obstacle [" << id_ << "] has no history";
     return;
   }
+  // If obstacle is not in the given junction, then exit.
   const std::string& junction_id = JunctionAnalyzer::GetJunctionId();
   if (!IsInJunction(junction_id)) {
     ADEBUG << "Obstacle [" << id_ << "] is not in junction [" << junction_id
            << "]";
     return;
   }
+
+  // Set the junction features by calling SetJunctionFeatureWithoutEnterLane.
   Feature* latest_feature_ptr = mutable_latest_feature();
   if (feature_history_.size() == 1) {
     SetJunctionFeatureWithoutEnterLane(latest_feature_ptr);
@@ -295,10 +299,14 @@ void Obstacle::SetJunctionFeatureWithEnterLane(const std::string& enter_lane_id,
 }
 
 void Obstacle::SetJunctionFeatureWithoutEnterLane(Feature* const feature_ptr) {
+  // Sanity checks.
   if (!feature_ptr->has_lane()) {
     ADEBUG << "Obstacle [" << id_ << "] has no lane.";
     return;
   }
+
+  // Get the possible lanes that the obstalce is on and their neighbor
+  // lanes and treat them as the starting-lane-segments.
   std::vector<std::string> start_lane_ids;
   if (feature_ptr->lane().current_lane_feature_size() > 0) {
     for (const auto& lane_feature :
diff --git a/modules/tools/prediction/data_pipelines/scripts/records_to_data_for_learning.sh b/modules/tools/prediction/data_pipelines/scripts/records_to_data_for_learning.sh
index c233f0b3c1..183dab9527 100644
--- a/modules/tools/prediction/data_pipelines/scripts/records_to_data_for_learning.sh
+++ b/modules/tools/prediction/data_pipelines/scripts/records_to_data_for_learning.sh
@@ -36,7 +36,6 @@ fi
     --flagfile=/apollo/modules/prediction/conf/prediction.conf \
     --map_dir=/apollo/modules/map/data/${MAP_DIR} \
     --prediction_offline_mode=2 \
-    --noenable_multi_thread \
     --prediction_offline_bags=${SRC_DIR} \
     --prediction_data_dir=${TARGET_DIR} \
     --noenable_multi_thread
-- 
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