ROS naviagtion analysis: costmap_2d--StaticLayer

从UML中能够看到，StaticLayer主要是在实现Layer层要求实现的接口。

  virtual void onInitialize();
  virtual void activate();
  virtual void deactivate();
  virtual void reset();
  virtual void updateBounds(double robot_x, double robot_y, double robot_yaw, double* min_x, double* min_y,double* max_x, double* max_y);
  virtual void updateCosts(costmap_2d::Costmap2D& master_grid, int min_i, int min_j, int max_i, int max_j);
  virtual void matchSize();

函数virtual void activate();：

void StaticLayer::activate()
{
  onInitialize();
}

而函数onInitialize() 中，首先初始化了一堆参数，然后调用

map_sub_ = g_nh.subscribe(map_topic, 1, &StaticLayer::incomingMap, this);//一旦收到topic 是“map”的消息，就调用`incomingMap`

    while (!map_received_ && g_nh.ok())
    {
 ros::spinOnce();
      r.sleep();
    }//如果map_received_一直是false，则阻塞在这里。而更新map_received_的地方在回调函数incomingMap

接下来判断是否接受static map的更新，如果是则开启对topic为map_topic + "_updates" 的更新。最后开启参数动态配置服务。

函数matchSize 中的操作依然是根据master map的尺寸，更新本层的尺寸：

void StaticLayer::matchSize()
{
  // If we are using rolling costmap, the static map size is
  // unrelated to the size of the layered costmap
  if (!layered_costmap_->isRolling())
  {
    Costmap2D* master = layered_costmap_->getCostmap();
    resizeMap(master->getSizeInCellsX(), master->getSizeInCellsY(), master->getResolution(),
              master->getOriginX(), master->getOriginY());
  }
}

函数interpretValue：
则是将参数根据阈值，设定为NO_INFORMATION FREE_SPACE LETHAL_OBSTACLE FREE_SPACE 或者其他值。

unsigned char StaticLayer::interpretValue(unsigned char value)
{
  // check if the static value is above the unknown or lethal thresholds
  if (track_unknown_space_ && value == unknown_cost_value_)
    return NO_INFORMATION;
  else if (!track_unknown_space_ && value == unknown_cost_value_)
    return FREE_SPACE;
  else if (value >= lethal_threshold_)
    return LETHAL_OBSTACLE;
  else if (trinary_costmap_)
    return FREE_SPACE;

  double scale = (double) value / lethal_threshold_;
  return scale * LETHAL_OBSTACLE;
}

以下分析回调函数incomingMap：

void StaticLayer::incomingMap(const nav_msgs::OccupancyGridConstPtr& new_map)
{
  unsigned int size_x = new_map->info.width, size_y = new_map->info.height;

  ROS_DEBUG("Received a %d X %d map at %f m/pix", size_x, size_y, new_map->info.resolution);

  // resize costmap if size, resolution or origin do not match
  //这里判断master map的尺寸是否和获取到的static map一致，如果不一致，则应该修改master map
  Costmap2D* master = layered_costmap_->getCostmap();
  if (!layered_costmap_->isRolling() && (master->getSizeInCellsX() != size_x ||
      master->getSizeInCellsY() != size_y ||
      master->getResolution() != new_map->info.resolution ||
      master->getOriginX() != new_map->info.origin.position.x ||
      master->getOriginY() != new_map->info.origin.position.y ||
      !layered_costmap_->isSizeLocked()))
  {
    // Update the size of the layered costmap (and all layers, including this one)
    ROS_INFO("Resizing costmap to %d X %d at %f m/pix", size_x, size_y, new_map->info.resolution);
    layered_costmap_->resizeMap(size_x, size_y, new_map->info.resolution, new_map->info.origin.position.x, new_map->info.origin.position.y, true);//修改了master map
  }
  //如果本层的数据和订阅到的map尺寸不一致，则更新本层的尺寸
  else if (size_x_ != size_x || size_y_ != size_y ||
           resolution_ != new_map->info.resolution ||
           origin_x_ != new_map->info.origin.position.x ||
           origin_y_ != new_map->info.origin.position.y)
  {
    // only update the size of the costmap stored locally in this layer
    ROS_INFO("Resizing static layer to %d X %d at %f m/pix", size_x, size_y, new_map->info.resolution);
    resizeMap(size_x, size_y, new_map->info.resolution,new_map->info.origin.position.x, new_map->info.origin.position.y);
  }

  unsigned int index = 0;

  // initialize the costmap with static data
  //这里将订阅拿到的map数据拷贝到了本层static map的数据成员`costmap_`
  for (unsigned int i = 0; i < size_y; ++i)
  {
    for (unsigned int j = 0; j < size_x; ++j)
    {
      unsigned char value = new_map->data[index];
      costmap_[index] = interpretValue(value);
      ++index;
    }
  }
  map_frame_ = new_map->header.frame_id;

  // we have a new map, update full size of map
  x_ = y_ = 0;
  width_ = size_x_;
  height_ = size_y_;
  map_received_ = true;
  has_updated_data_ = true;

  // shutdown the map subscrber if firt_map_only_ flag is on
  if (first_map_only_)
  {
    map_sub_.shutdown();
  }
}

函数 updateBounds 这里设定为整张static map的大小：

void StaticLayer::updateBounds(double robot_x, double robot_y, double robot_yaw, double* min_x, double* min_y,
                               double* max_x, double* max_y)
{

  if( !layered_costmap_->isRolling() ){
    if (!map_received_ || !(has_updated_data_ || has_extra_bounds_))
      return;
  }

  useExtraBounds(min_x, min_y, max_x, max_y);

  double wx, wy;

  mapToWorld(x_, y_, wx, wy);
  *min_x = std::min(wx, *min_x);
  *min_y = std::min(wy, *min_y);

  mapToWorld(x_ + width_, y_ + height_, wx, wy);
  *max_x = std::max(wx, *max_x);
  *max_y = std::max(wy, *max_y);

  has_updated_data_ = false;
}

函数 updateCosts：

void StaticLayer::updateCosts(costmap_2d::Costmap2D& master_grid, int min_i, int min_j, int max_i, int max_j)
{
  if (!map_received_)
    return;

  if (!layered_costmap_->isRolling())
  {
    // if not rolling, the layered costmap (master_grid) has same coordinates as this layer这里如果不是rolling 选项，则直接将本层数据copy到master map，因为它们尺寸也一样
    if (!use_maximum_)
      updateWithTrueOverwrite(master_grid, min_i, min_j, max_i, max_j);
    else
      updateWithMax(master_grid, min_i, min_j, max_i, max_j);
  }
  else
  {
    // If rolling window, the master_grid is unlikely to have same coordinates as this layer
    unsigned int mx, my;
    double wx, wy;
    // Might even be in a different frame
    //首先获得map坐标系相对于global坐标系的位置，这个时候的map坐标系是随着机器人运动而运动的。
    tf::StampedTransform transform;
    try
    {
      tf_->lookupTransform(map_frame_, global_frame_, ros::Time(0), transform);
    }
    catch (tf::TransformException ex)
    {
      ROS_ERROR("%s", ex.what());
      return;
    }
    // Copy map data given proper transformations
    for (unsigned int i = min_i; i < max_i; ++i)
    {
      for (unsigned int j = min_j; j < max_j; ++j)
      {
        // Convert master_grid coordinates (i,j) into global_frame_(wx,wy) coordinates
        layered_costmap_->getCostmap()->mapToWorld(i, j, wx, wy);
        // Transform from global_frame_ to map_frame_
        tf::Point p(wx, wy, 0);
        p = transform(p);
        // Set master_grid with cell from map
        if (worldToMap(p.x(), p.y(), mx, my))
        {
          if (!use_maximum_)
            master_grid.setCost(i, j, getCost(mx, my));
          else
            master_grid.setCost(i, j, std::max(getCost(mx, my), master_grid.getCost(i, j)));
        }
      }
    }
  }
}

重点是这两句：

      if (worldToMap(p.x(), p.y(), mx, my))
        {
          if (!use_maximum_)
            master_grid.setCost(i, j, getCost(mx, my));

将static map层的每一点（i，j），都找到对应的master map的（mx，my），这样就可以直接更改master map的对应点了。
OK，静态地图分析到此为止～接下来分析Obstacle 层，这个略微要难点。