Data from Simulink does not update ROS2 topic

Hello. I am trying to send a message to a topic. My message seems to have the correct data when seen in simulink, but my ros2 topic is not getting updated with this data.

System:

Ubuntu 20.04

Matlab R2022b

ROS2 Humble

Here is my Simulink block:

I have two message files:

VPGWaypoints.msg

std_msgs/Header header

Waypoint[] wps

Waypoint.msg

float64 x

float64 y

float32 theta

float32 vref

Inside the matlab function - Assign:

What I am trying to do is write a new message of type VPGWaypoints and publish it to the topic /control/velocity_profile with a list of Waypoints messages. I do not know how to create a list/array of custom messages. The function assignArray is my attempt that doing so by modifying the field wps directly. As you can see in the first screenshot, the data is correctly getting updated. x=1.57 in the first element, y=1.57 in the second element. However, in my terminal, when I run ros2 topic echo /control/velocity_profile , all I see is an empty list :

Answer 1

[Josh Chen]

Hello Renzo,

When publishing messages with vector fields in Simulink, Simulink needs to know the length of valid data in those fields. This information is captured under "xxx_SL_Info.CurrentLength".

In your case, you can add the following line at the end of your MATLAB Function block:

msg.wps_SL_Info.CurrentLength = int32(2);

You may also find this page helpful - Work with ROS Messages in Simulink

Hope this helps,

Josh

[Renzo]

Thank you! That solved it