Joep Linssen asked . 2023-05-15

Error in readMessages from generated ROS message

Reference to non-existent field 'Forces_'.

Error in robotics.ros.custom.msggen.sfm_msgs.Forces/reload (line 165)
          Forces_Cell = arrayfun(@(x) feval([obj.SfmMsgsForceClass '.loadobj'], x), strObj.Forces_, 'UniformOutput', false);

Error in robotics.ros.Message/fromStruct (line 172)
              obj.reload(sObj);

Error in robotics.ros.BagSelection/readMessages (line 280)
                  msgs{i}.fromStruct(msgStructs{i});

I did some investigation on how the function works and where the error comes from. In

robotics.ros.Message/fromStruct

the code tries to create a message object from the bag information (which is in struct format). For my custom message of type

sfm_msgs/Forces

the field names for the message and the structs (these are autogenerated by rosgenmsg) differ:

K>> msgs{1}

ans = 

ROS Forces message with properties:

    MessageType: 'sfm_msgs/Forces'
         Header: [1×1 Header]
        Forces_: [0×1 Force]

versus

K>> msgStructs{1}

ans = 

struct with fields:

    MessageType: 'sfm_msgs/Forces'
         Header: [1×1 struct]
         Forces: [1×6 struct]

std_msgs/Header header
Force[] forces

Force.msg:

uint8 ATTRACTIVE=0
uint8 INT_ROBOT=1
uint8 INT_OBSTACLE=2
uint8 INT_HUMAN=3
uint8 type
string entity_name
geometry_msgs/Vector3 force

Robotics and Autonomous Systems , ROS Toolbox , ROS Specialized Messages