Custom ROS msg type does not get added to rosmsg list even after MATLAB restart

I'm following this guide to create a custom ROS message type (https://www.mathworks.com/help/robotics/ug/ros-custom-message-support.html).

This is the structure of my msg

path_planning_msgs FOLDER 
--- path_planning_msgs FOLDER 
    --- package.xml (copied from guide, replace w <name>path_planning_msgs</name> 
    --- Path.msg

Contents of package.xml

<package>
    <name>path_planning_msgs</name>
    <version>1.1.01</version>
    
    <build_depend>message_generation</build_depend>
    <build_depend>geometry_msgs</build_depend>
    <build_depend>std_msgs</build_depend>
</package>

Contents of Path.msg

Header header

path_planning_msgs/VehicleState[] states

Then I executed these commands and everything seemed to work (I'm on Ubuntu 16.04 LTS)

Then I edited javaclasspath.txt to add the line

Then I ran the addpath and savepath

Then I closed MATLAB to restart it.

Then I checked rosmsg list but the path_planning_msgs/Path type is nowhere to be found.

Thank you in advance.

Answer 1

[Sebastian Castro]

Hi An,

Pretty sure the ROS package requires your .msg file to be inside a subfolder called msg.

So your folder structure should be as follows:

path_planning_msgs FOLDER

--- package.xml

--- msg FOLDER

--- Path.msg

Try that and let us know if it works!

- Sebastian

[An Nguyen]

Thank you very much for your lightning-fast reply.

In the first picture, I tried your suggested structure.

Then I tried moving package.xml into the msg folder which resulted in

I did not modify the contents of any file.

[Sebastian Castro]

Your first picture is the correct folder structure... but it appears you have called rosgenmsg from one folder too low, because that matlab_gen folder should not be there. I assume nothing was generated.

You should go to the folder containing your path_planning_msgs package as follows:

CURRENT_FOLDER

--- path_planning_msgs FOLDER

--- package.xml

--- msg FOLDER

---- Path.msg

And from there call

>> rosgenmsg .

Alternatively, to follow the way you tried things, your path variable should be one folder up...

>> path = 'home/annwin/Desktop';

>> rosgenmsg(path);

- Sebastian

[Sebastian Castro]

One more observation... if your Path.msg is defined like this:

path_planning_msgs/VehicleState[] states

Shouldn't you also have a VehicleState.msg definition file somewhere in this folder?

- Sebastian

[An Nguyen]

Great observation. Following the steps above, I have successfully created a custom message type for VehicleState.msg as shown in the picture below.

However, I am running into a different issue when replicating those steps to build Path.msg.

I am going to search around for a solution and will keep you updated with my progress. Thank you!

[Sebastian Castro]

An,

That latest error is exactly because you don't have a VehicleState.msg file defined! If you look at the error text it will show you it's pointing at an undefined symbol "VehicleState".

By the way, in future it would be much more useful instead of screenshots to copy-paste the error message text. This makes the question searchable if others have similar errors!

- Sebastian

[An Nguyen]

I am sorry for not getting back to you sooner. My team and I were trying to get it to work this morning and have finally succeeded after many trials. We finally got our ROS node!

We were not aware that the Path.msg and VehicleState.msg are supposed to be kept together under folder msg to be generated in one run. Initially we placed VehicleState.msg under its own directory thinking that we would need to define it first before moving on to Path.msg.

In case people search for this issue later, our final structure is

path_planning_msgs FOLDER 
--- package.xml  (add a build_depend line for VehicleState)
--- msg FOLDER 
    --- Path.msg 
    --- VehicleState.msg 

We had been on the issue for days and would not have been able to solve it this fast without your feedback! Thank you very much for your help.