ROS2 unable to use "Write Image" block = error in WriteImageFcnBlock.m

Hi everyone - I am trying out the ROS2 toolbox for Simulink, and can't successfully use the ROS2 Write Image block. I have loaded a demo image to the workspace using testImg = imread("free-images.jpg"), and it is loading as a 800x1200x3 uint8 variable. I have loaded it into Simulink using "Image From Workspace", and sent it into the ROS2 Write Image block with rgb8 encoding. Unfortunately I get the error below, and other encoding options also don't work. Any help? I have attached the error and setup below.

An error occurred during simulation and the simulation was terminated

Caused by:

Index exceeds array dimensions. Index value 129 exceeds valid range [1-128].

Error in WriteImageFcnBlock.m (line 25)

Data(1:DataLength) = Data1(1:DataLength);

Error in 'aprilTagTest/Write Image/MATLAB Function' (line 30)

Answer 1

[Jagadeesh Konakalla]

Hi Dylan,

Please follow the example on how to access variable length array ROS messages in Simulink. You need to set the Maximum Size of a Variable-length Array in your Simulink model.

Work with ROS Messages in Simulink - MATLAB & Simulink (mathworks.com)

Thanks and regards,

Jagadeesh K

[Dylan]

Thank you so much! That is the solution.

[Dylan]

Out of curiosity, is there a way to dynamically set the size of the relevant variable-length array based on a variable from the workspace?