How do I enter a string into a ROS message in Simulink?

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Harry Parsons
Harry Parsons el 21 de Sept. de 2020
Respondida: Josh Chen el 26 de Oct. de 2020
I'm attempting to send a path message to a ROS system. However, in order for this to be correctly published to RVIZ it requires a reference frame ID (FrameId in the header). I have attempted to complete this in multiple ways- First I attempted to enter a String Constant into a bus assignment block:
This has come up with the following error:
I then attempted in the shown matlab block to create a 128x1 uint8 array of the ASCII values of "odom", and blank characters (ASCII 32) making up the remaining 124 characters, using the following code:
frameid = zeros(128,1, 'uint8');
string = ['o', 'd', 'o', 'm'];
frameid(1:4) = uint8(string);
frameid(5:128) = 32;
frameid = uint8(frameid);
globalplannermessage.Header.FrameId = frameid;
This, however, simply ended up with RVIZ showing that the reference frame was blank (For frame []: Frame [] does not exist)
What is the recommended method to complete this?
This is my first question on here, so if I have missed any important information please let me know and I'll change whatever needs to be changed!

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Josh Chen
Josh Chen el 26 de Oct. de 2020
Hello Harry,
Since ROS strings in Simulink have to be fixed-length uint8 array, normally there are two ways of entering a string into a ROS message in Simulink.
(1) Use a MATLAB Function block to convert a string to uint8. Refer to the following page as an example:
(2) Use the "String to ASCII" block to convert the string signal to uint8 array.
Hope this helps,
-Josh

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