激光雷达的位置如下图所示，车体右侧面激光雷达：

静态TF：

  <node pkg="tf" type="static_transform_publisher" name="base_link_to_laser4"
    args="0.0 -0.3 0.7 -1.57 0.0 0.0  /base_link /ydlidar_right_frame 40" />

1.方法一：利用tf进行坐标变换

// trans pos in raser to global
Raser_3dPoint get_global_pos(Raser_3dPoint &pos)
{
  std::cout<<"pos in laser"<<"  x:"<<pos.x<<"  y:"<<pos.z<<"  z:"<<pos.y<<std::endl;
  Raser_3dPoint res;
	//创建TF监听器
	tf::TransformListener listener;
	geometry_msgs::PointStamped laser_point;
	laser_point.header.frame_id = "ydlidar_right_frame";
	//使用最近可用的转换
	laser_point.header.stamp = ros::Time();

	laser_point.point.x = pos.x;
	laser_point.point.y = pos.z;
	laser_point.point.z = 0.0;
   
  geometry_msgs::PointStamped world_point;	
  try
	{
		//监听获取tf变换
		listener.waitForTransform("odom", "ydlidar_right_frame", ros::Time(0), ros::Duration(3.0));
		world_point.header.frame_id = "odom";
		listener.transformPoint("odom", laser_point, world_point);
	}
	catch(tf::TransformException& ex)
	{
		ROS_ERROR("%s", ex.what());
		ros::Duration(1.0).sleep();
	}
  res.x = world_point.point.x;
  res.y = world_point.point.y;
  res.z = world_point.point.z;
  std::cout<<"pos in world"<<"  x:"<<res.x<<"  y:"<<res.y<<"  z:"<<res.z<<std::endl;
  return res;
}

得到的变化结果如下：

target pos to laser:x 0.0840537 y 0 z 0.498975 valid points 138
pos in laser  x:0.0840537  y:0.498975  z:0
pos in base  x:0.499042  y:-0.383656  z:0.7

方法二：直接利用变换矩阵进行坐标变换
首先需要订阅得到当前的小车Pose，即里程计信息，以下是忽略激光和车体之间的变化的情况，默认重合。
如果激光里程计和车体存在旋转和平移，需要先将激光点云数据转换从laser frame转换到base link下。

Eigen::Vector3d robotPose(robotPose_x,robotPose_y,robotPose_theta);
//计算得到该激光点的世界坐标系的坐标
double theta = -robotPose(2); // 激光雷达逆时针转，角度取反
//double laser_x = dist * cos(angle);
//double laser_y = dist * sin(angle);
double laser_x = pos.x;
double laser_y = pos.z;
//double laser_z = pos.z;
  
double world_x = cos(theta) * laser_x - sin(theta) * laser_y + robotPose(0);
double world_y = sin(theta) * laser_x + cos(theta) * laser_y + robotPose(1);
  
res.x = world_x;
res.y = world_y;
res.z = 0.7;
return res;

实际上在使用时，使用TF变化坐标延迟太高，建议自己转换。