ROS:一种简单的基于global_planner的全局路径优化方法

一种简单的基于global_planner的全局路径优化方法

代码链接：
https://download.csdn.net/download/qq_14977553/12688247
或者
https://github.com/li-huanhuan/ros-melodic-global-planner

环境：

Ubuntu 18.04.4 LTS
ros-melodic
修改的包：navigation中global_planner功能包
全局规划器使用dijkstra算法

优化目标：

1、使路径与膨胀层保持一个像素点的距离。
2、使绕障碍物的路径更加平滑。

优化之前的路径

第一步：添加路径规划约束条件

文件：dijkstra.cpp

函数

inline void DijkstraExpansion::updateCell(
                                unsigned char*costs,
                                float* potential, 
                                int n)

修改为：

inline void DijkstraExpansion::updateCell(unsigned char* costs, float* potential, int n)
{
    cells_visited_++;

    // do planar wave update
    float c = getCost(costs, n);
    if (c >= lethal_cost_)    // don't propagate into obstacles
        return;

    float c_near[8] = {0};
    int np = n - nx_;
    int nn = n + nx_;
    c_near[0] = getCost(costs, np-1);
    c_near[1] = getCost(costs, np);
    c_near[2] = getCost(costs, np+1);

    c_near[3] = getCost(costs, n-1);
    c_near[4] = getCost(costs, n+1);

    c_near[5] = getCost(costs, nn-1);
    c_near[6] = getCost(costs, nn);
    c_near[7] = getCost(costs, nn+1);

    for(unsigned int i=0;i<8;i++)
    {
      if(c_near[i] > 50)
      {
        return;
      }
    }

    float pot = p_calc_->calculatePotential(potential, c, n);

    // now add affected neighbors to priority blocks
    if (pot < potential[n])
    {
        float le = INVSQRT2 * (float)getCost(costs, n - 1);
        float re = INVSQRT2 * (float)getCost(costs, n + 1);
        float ue = INVSQRT2 * (float)getCost(costs, n - nx_);
        float de = INVSQRT2 * (float)getCost(costs, n + nx_);
        potential[n] = pot;
        //ROS_INFO("UPDATE %d %d %d %f", n, n%nx, n/nx, potential[n]);
        if (pot < threshold_)    // low-cost buffer block 
        {
            if (potential[n - 1] > pot + le)
                push_next(n-1);
            if (potential[n + 1] > pot + re)
                push_next(n+1);
            if (potential[n - nx_] > pot + ue)
                push_next(n-nx_);
            if (potential[n + nx_] > pot + de)
                push_next(n+nx_);
        }
        else            // overflow block
        {
            if (potential[n - 1] > pot + le)
                push_over(n-1);
            if (potential[n + 1] > pot + re)
                push_over(n+1);
            if (potential[n - nx_] > pot + ue)
                push_over(n-nx_);
            if (potential[n + nx_] > pot + de)
                push_over(n+nx_);
        }
    }
}

优化后:

第二步：增加路径点的密度

文件：planner_core.cpp
函数：

bool GlobalPlanner::getPlanFromPotential(double start_x, double start_y,
                                         double goal_x, double goal_y,
                                         const geometry_msgs::PoseStamped& goal,
                                         std::vector<geometry_msgs::PoseStamped>& plan)

修改为：

bool GlobalPlanner::getPlanFromPotential(double start_x, double start_y,
                                         double goal_x, double goal_y,
                                         const geometry_msgs::PoseStamped& goal,
                                         std::vector<geometry_msgs::PoseStamped>& plan)
{
    if (!initialized_)
    {
        ROS_ERROR("This planner has not been initialized yet, but it is being used, please call initialize() before use");
        return false;
    }

    std::string global_frame = frame_id_;

    //clear the plan, just in case
    plan.clear();

    std::vector<std::pair<float, float> > path;

    if (!path_maker_->getPath(potential_array_, start_x, start_y, goal_x, goal_y, path))
    {
        ROS_ERROR("NO PATH!");
        return false;
    }

    ros::Time plan_time = ros::Time::now();
    int path_size_num = path.size() -1;
    for (int i = path_size_num; i>=0; i--)
    {
        std::pair<float, float> point = path[i];
        //convert the plan to world coordinates
        double world_x, world_y;
        mapToWorld(point.first, point.second, world_x, world_y);

        geometry_msgs::PoseStamped pose;
        pose.header.stamp = plan_time;
        pose.header.frame_id = global_frame;
        pose.pose.position.x = world_x;
        pose.pose.position.y = world_y;
        pose.pose.position.z = 0.0;
        pose.pose.orientation.x = 0.0;
        pose.pose.orientation.y = 0.0;
        pose.pose.orientation.z = 0.0;
        pose.pose.orientation.w = 1.0;

        if(i != path_size_num)
        {
          double cx,cy,px,py;
          cx = pose.pose.position.x;
          cy = pose.pose.position.y;
          px = plan.back().pose.position.x;
          py = plan.back().pose.position.y;
          if( sqrt( (cx-px)*(cx-px) + (cy-py)*(cy-py) ) > 0.05)
          {
            geometry_msgs::PoseStamped pose_insert = pose;
            pose_insert.pose.position.x = (cx+px)/2;
            pose_insert.pose.position.y = (cy+py)/2;
            plan.push_back(pose_insert);
          }
        }
        plan.push_back(pose);
    }
    if(old_navfn_behavior_)
    {
        plan.push_back(goal);
    }
    return !plan.empty();
}

优化后：

第三步：路径平滑

修改文件：planner_core.cpp
添加路径平滑函数和角度标准化函数：

平滑函数声明：

int optimizationPath(
std::vector<geometry_msgs::PoseStamped>& plan,
double movement_angle_range=M_PI_4);

标准化函数为：

 double inline normalizeAngle(
                    double val,
                    double min = -M_PI,
                    double max = M_PI)
{
          float norm = 0.0;
          if (val >= min)
            norm = min + fmod((val - min), (max-min));
          else
            norm = max - fmod((min - val), (max-min));

          return norm;
}

平滑函数定义：

int GlobalPlanner::optimizationPath(
          std::vector<geometry_msgs::PoseStamped>& plan,
          double movement_angle_range)
{
  if(plan.empty())
    return 0;
  size_t pose_size = plan.size() - 1;
  double px,py,cx,cy,nx,ny,a_p,a_n;
  bool is_run = false;
  int ci = 0;
  for(ci=0;ci<1000;ci++)
  {
    is_run = false;
    for(size_t i=1;i<pose_size;i++)
    {
      px = plan[i-1].pose.position.x;
      py = plan[i-1].pose.position.y;

      cx = plan[i].pose.position.x;
      cy = plan[i].pose.position.y;

      nx = plan[i+1].pose.position.x;
      ny = plan[i+1].pose.position.y;

      a_p = normalizeAngle(atan2(cy-py,cx-px),0,2*M_PI);
      a_n = normalizeAngle(atan2(ny-cy,nx-cx),0,2*M_PI);

      if(std::max(a_p,a_n)-std::min(a_p,a_n) > movement_angle_range)
      {
        plan[i].pose.position.x = (px + nx)/2;
        plan[i].pose.position.y = (py + ny)/2;
        is_run = true;
      }
    }
    if(!is_run)
      return ci;
  }
  return ci;
}

在planner_core.cpp的

bool GlobalPlanner::makePlan(const geometry_msgs::PoseStamped& start,
                             const geometry_msgs::PoseStamped& goal,
                             double tolerance,
                             std::vector<geometry_msgs::PoseStamped>& plan)

中调用路径平滑函数，调用位置为：

 if (found_legal)
    {
        //extract the plan
        //从可行点矩阵提取路径
        if (getPlanFromPotential(start_x, start_y, goal_x, goal_y, goal, plan))
        {
            //make sure the goal we push on has the same timestamp as the rest of the plan
            geometry_msgs::PoseStamped goal_copy = goal;
            goal_copy.header.stamp = ros::Time::now();
            plan.push_back(goal_copy);
            this->optimizationPath(plan,M_PI/10); //此处调用路径平滑函数
        }
        else
        {
            ROS_ERROR("Failed to get a plan from potential when a legal potential was found. This shouldn't happen.");
        }
    }
    else
    {
        ROS_ERROR("Failed to get a plan.");
    }

最终效果：

总结：

效果对比图：

请根据具体场景灵活使用该方法。。