How do I properly generate code to set the topic name for a ROS 2 publisher using the value of the getParameter(...) function?
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Sam
el 9 de Ag. de 2023
Comentada: Josh Chen
el 11 de Abr. de 2024
A basic test example:
function testROS2Node()
% Create ROS 2 Node
nodeParams.topicName = 'test';
node = ros2node("/test", 0, Parameters=nodeParams);
% Get the parameter
topicName = getParameter(node, "topicName", Datatype="string");
% Create the publisher
pub = ros2publisher(node, topicName, "std_msgs/Bool");
% Loop rate to 1 Hz
r = ros2rate(node, 1);
while(1)
% Create and send a message every cycle.
msg = ros2message("std_msgs/Bool");
msg.data = true;
send(pub, msg);
waitfor(r);
end
end
The coder commands:
cfg = coder.config('exe');
cfg.Hardware = coder.hardware('Robot Operating System 2 (ROS 2)');
cfg.Hardware.DeployTo = 'Localhost';
cfg.Hardware.BuildAction = 'Build and Load';
cfg.TargetLang = 'C++';
cfg.InlineBetweenUserFunctions = 'Readability';
codegen('-config', cfg, 'testROS2Node');
The error:
Expression could not be reduced to a constant.
Error in ==> ros2publisher Line: 183 Column: 22
Code generation failed: View Error Report
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Josh Chen
el 9 de Ag. de 2023
Hi Sam,
Unfortunately, the topicName input for ros2publisher has to be a constant. Since parameter value is not constant, you cannot create the publisher with it.
Can you please share more about the workflow? Is there a reason you would like to create a publisher using the parameter?
Thanks,
Josh
3 comentarios
Erwin Mathew Louis
el 11 de Abr. de 2024
Editada: Erwin Mathew Louis
el 11 de Abr. de 2024
Hello,
Just a quick question to this. In case it was a regular parameter and not a topic name, would I be able to change the value from the terminal when the generated C++ code of the node created in matlab is running? There isnt much documentation about how matlab handles such changes to parameters. I guess I am mainly asking about the parameter callback functionality available in ros2. are such callback available in the ROS toolbox?
Josh Chen
el 11 de Abr. de 2024
Hi Erwin,
If I understand you correctly, you are referring to ROS 2 parameters associated with ROS 2 nodes. Yes, this is supported for code generation. You can specify all parameters with the "Parameters" name-value pair when creating the node object.
When generating code from MATLAB, those parameters will be generated as ROS 2 parameters for the associated ROS 2 node.
As for parameter callbacks, could you please give some more information about what you are planning to achieve/do inside each callback?
Thanks,
Josh
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