Little elevation map in velodyne 16 lidar!

[KJ-Falloutlast]

Really thankful for your masterpiece, but I have a problem:
I've already set my urdf and config file as the tutorial did as following, but I can't not get the elevator map. please help me with this problem, and I would be appreciate!

• this is my console output:
  
• this is my config:

input_sources:                                                                  
  front:                                                                        
    type: pointcloud                                                            
    topic: /velodyne_points/points_downsampled                               
    queue_size: 10           #queue_size 必须大于5才行                                                  
    publish_on_update: true                                                     
    sensor_processor:                                                           
      type: laser                                                               
      #ignore_points_above: 0.0                                                 
      #ignore_points_below: -4.0                                                
      min_radius: 0.018                                                         
      beam_angle: 0.0006                                                        
      beam_constant: 0.0015                                                     
map_frame_id: "odom"                                                             
robot_base_frame_id: "base_link"                                                
robot_pose_with_covariance_topic: "/base_link_pose"                             
robot_pose_cache_size: 200                                                      
track_point_frame_id: "base_link"  
length_in_x: 5                                                                     
length_in_y: 5                                                                     
position_x: 0.0                                                                    
position_y: 0.0                                                                    
resolution: 0.08                                                                   
min_variance: 0.00009                                                              
max_variance: 0.01                                                                 
mahalanobis_distance_threshold: 2.5                                                
multi_height_noise: 0.00002
sensor_frame_id: "velodyne" #velodyne

• this is my tf_tree
  

[KJ-Falloutlast]

the map is just like this, which is so weird!