21、 TF coordinate transformation (I): coordinate MSG message

One 、 introduction

In the process of robot movement , Need to sense the orientation of surrounding objects through sensors . Because the sensor and robot are not in the same coordinate system , So we need to transform the coordinate system . stay ROS in , It directly encapsulates the relevant modules ： Coordinate transformation （TF）
stay ROS In the system , The object is calibrated through the right-hand coordinate system , As shown in the figure below ：

be relative to tf,tf2 More concise and efficient , Common function packs include ：

• tf2_geometry_msgs: Can be ROS The message is converted to tf2 news .

• tf2: Encapsulates common messages of coordinate transformation .

• tf2_ros: by tf2 Provides roscpp and rospy binding , Encapsulates the commonly used coordinate transformation API

Two 、 coordinate msg news

2.1 Commonly used msg

• geometry_msgs/TransformStamped： Transmit position information related to different coordinate systems

  std_msgs/Header header                     # Header information 
  uint32 seq                                #|--  Serial number 
  time stamp                                #|--  Time stamp 
  string frame_id                            #|--  coordinate  ID
  string child_frame_id                    # Of the sub coordinate system  id
  geometry_msgs/Transform transform        # Coordinate information 
  geometry_msgs/Vector3 translation        # Offset 
      float64 x                                #|-- X  Offset of direction 
      float64 y                                #|-- Y  Offset of direction 
      float64 z                                #|-- Z  The offset in the direction 
  geometry_msgs/Quaternion rotation        # Four yuan number 
      float64 x                                
      float64 y                                
      float64 z                                
      float64 w
  

• geometry_msgs/PointStamped： Transmit the information of coordinate points in a coordinate system

  std_msgs/Header header                    # head 
  uint32 seq                                #|--  Serial number 
  time stamp                                #|--  Time stamp 
  string frame_id                            #|--  Of the coordinate system  id
  geometry_msgs/Point point                # Point coordinates 
  float64 x                                    #|-- x y z  coordinate 
  float64 y
  float64 z