从apollo2.0的代码上看，百度是想做lidar和radar融合的
先看传感器输出数据定义
class SensorRawFrame
{
public:
SensorType sensortype;
double timestamp;
Eigen::Matrix4d pose;
};
// lidar输出数据定义，用的是Velodyne的产品，包含了一块点云，pcl库格式
class Velodyne的产品RawFrame : public SensorRawFrame
{
public:
VelodyneRawFrame() {}
~VelodyneRawFrame() {}
public:
pclutil::PointCloudPtr cloud;
};
// radar输出数据定义，用的是大陆的产品，包含了一个ContiRadar成员
class RadarRawFrame : public SensorRawFrame
{
public:
RadarRawFrame() {}
~RadarRawFrame() {}

public:
ContiRadar rawobstacles;
Eigen::Vector3f car_linearspeed;
};
ContiRadar定义在Conti_Radar.proto中
message ContiRadar
{
optional apollo.common.Header header = 1;
repeated ContiRadarObs contiobs = 2; //conti radar obstacle array
optional RadarState_201 radar_state = 3;
optional ClusterListStatus_600 cluster_list_status = 4;
optional ObjectListStatus_60A object_list_status = 5;
}
ContiRadarObs是最重要的部分，代表了radar输出的一个目标点，同样定义在Conti_Radar.proto中
message ContiRadarObs
{
optional apollo.common.Header header = 1;
optional bool clusterortrack = 2; // 0 = track, 1 = cluster
optional int32 obstacle_id = 3; // obstacle Id
required double longitude_dist = 4;
required double lateral_dist = 5;
required double longitude_vel = 6;
required double lateral_vel = 7;
optional double rcs = 8;
optional int32 dynprop = 9;
optional double longitude_dist_rms = 10;
optional double lateral_dist_rms = 11;
optional double longitude_vel_rms = 12;
optional double lateral_vel_rms = 13;
optional double probexist = 14;

//The following is only valid for the track object message
optional int32 meas_state = 15;
optional double longitude_accel = 16;
optional double lateral_accel = 17;
optional double oritation_angle = 18;
optional double longitude_accel_rms = 19;
optional double lateral_accel_rms = 20;
optional double oritation_angle_rms = 21;
optional double length = 22;
optional double width = 23;
optional int32 obstacle_class = 24;
}
值得注意的是百度增加了rcs，虽然2.0的代码未用到rcs。

入口函数，整个函数做了两件事，
1.根据sensor_type_分别处理lidar和radar
2.lidar和radar融合
本次只分析radar，lidar和融合下次再写
bool ObstaclePerception::Process(SensorRawFrame frame, std::vector out_objects)
{
std::shared_ptr sensor_objects(new SensorObjects());
if (frame->sensortype == VELODYNE_64)
{
}
else if (frame->sensortype == RADAR)
{
// radar处理
RadarRawFrame radar_frame = dynamic_cast>(frame);
RadarDetectorOptions options;
options.radar2world_pose = &(radarframe->pose);
options.car_linear_speed = radar_frame->car_linearspeed;
std::vector objects;
std::vector map_polygons;
if (!radardetector->Detect(radar_frame->rawobstacles, map_polygons,
options, &objects)) {
AERROR << "Radar perception error!, " << std::fixed
<< std::setprecision(12) << radarframe->timestamp;
return false;
}
sensor_objects->objects = objects;
AINFO << "radar objects size: " << objects.size();
PERF_BLOCK_END("radar_detection");
// set frame content
if (FLAGS_enable_visualization && FLAGS_show_radar_obstacles) {
framecontent.SetTrackedObjects(sensor_objects->objects);
}
}
}
radar处理两个不步骤
1.调用bool ModestRadarDetector::Detect函数，输出检测跟踪之后的objects
2.objects保存到framecontent，用于融合

bool ModestRadarDetector::Detect
{

  1. 调用void ObjectBuilder::Build(const ContiRadar &raw_obstacles,
    const Eigen::Matrix4d &radar_pose,
    const Eigen::Vector2d &main_velocity,
    SensorObjects *radar_objects)
    这个build函数根据raw_obstacles原始数据，构建Object对象，Object的定义是lidar和radar共用的
    这里面有做了几个重要的事
    1. radar坐标转化车身坐标，相对速度转为绝对速度
    2. 判断目标是否is_background，这个判断的条件比较有意思
      情况1：比较出现的次数，目标出现的次数小于delay_frames_的is_background
      if (current_con_ids[obstacle_id] <= delayframes)
      {
      object_ptr->is_background = true;
      }
      情况2：
      ContiRadarUtil::IsFp(raw_obstacles.contiobs(i), contiparams,
      delayframes, tracking_times))
      情况3：比较目标速度和车身速度的夹角，(1/4Pi，3/4Pi) (-1/4Pi，-3/4Pi)范围的不是background
      if (ContiRadarUtil::IsConflict(ref_velocity, object_ptr->velocity.cast()))
      {
      object_ptr->is_background = true;
      }
      1. 计算目标的外包矩形，radar是没有目标形状信息的，百度自己把长宽高都设为1，吐槽
        RadarUtil::MockRadarPolygon(point, object_ptr->length, object_ptr->width,
        theta, &(object_ptr->polygon));
  2. 调用void RadarTrackManager::Process(const SensorObjects &radar_obs)
    {
    radarobs = radar_obs;
    Update(&radarobs);
    }
    update函数
    1. AssignTrackObsIdMatch(radar_obs, &assignment, &unassigned_track, &unassigned_obs);
      id相同，并且距离小于2.5的是同一个目标
      百度计算距离没有像lidar那样用卡尔曼预测一步，直接当前速度       时间差来预测，吐槽
      1. UpdateAssignedTrack(*radar_obs, assignment);
        用匹配到的object更新轨迹，百度没有保存radar轨迹的历史点，lidar是保留了轨迹历史点的
    2. UpdateUnassignedTrack((*radar_obs).timestamp, unassigned_track);
      对于没有匹配到object的轨迹，如果持续0.06没有匹配到object，就置为null
    3. DeleteLostTrack();
      删除null的轨迹
    4. CreateNewTrack(*radar_obs, unassigned_obs);
      没有匹配到轨迹的object建立新的轨迹
      1. 调用bool ModestRadarDetector::CollectRadarResult(std::vector *objects)
        非background的track输出到objects
        }
        总结一下：
      2. 预留了rcs，没用到
      3. 计算距离前预测方式太简单
      4. radar的目标长宽高自定义1.0，
      5. ROI预留了map_polygons这个变量，但是目前empty，未向lidar那样从hadmap得到ROI区域