How to pass a variable to my callback function through rossubscriber

Hey guys. so i'm trying to create a call back function which looks like this:

odomCallback function

function [] = odomCallback(~,odomMsg, fig, varargin)

figure(fig);%set figure

title('callbackfigure');%set figure title

clf;

hold on;

[ x1, y1, ~ ] = OdometryMsg2Pose( odomMsg ); % convert odom message to pose vector

plot(x1,y1,'--rx');%plot figure

% plot pose vector with quiver

end

main

fig = 3;%figure 3

odomSubCallback = rossubscriber('/odom', {@odomCallback,odomMsg,fig},"DataFormat","struct");%wrong definition % doesn't work

clear odomSubCallback; %clear var

Suddenly the way i called my function in the main and how i passed my variables was wrong could someone tell me how to do it correctly.

thanks in advance

Answer 1

[Cam Salzberger]

Hello Zakaria,

If you were to assign the NewMessageFcn subscriber property to just a callback function:

odomSub.NewMessageFcn = @odomCallback;

then the expected signature would look like:

function odomCallback(src, msg)

In this, the "src" is the subscriber and the "msg" is the ROS message that has been sent by the publisher.

You are using a cell array to pass additional arguments. For example:

odomSub.NewMessageFcn = {@odomCallback, arg1, arg2};

then the expected signature would look like:

function odomCallback(src, msg, arg1, arg2)

But you are passing "odomMsg" as "arg1" here. So your function is getting:

function odomCallback(odomSub, msgSentFromPub, originalProbablyBlankMsg, figureNumber)

I believe you should just be setting the callback to:

{@odomCallback,fig}

unless you really need that original blank message to operate on. I personally prefer to use anonymous functions to make it clear what the function signature is expected to be (also removing the "src" argument if not necessary):

odomSub.NewMessageFcn = @(~, msg) odomCallback(msg, fig);

with signature:

function odomCallback(msg, fig)

Other advice:

• Consider passing a figure handle rather than a number. It's more guaranteed.
• Consider specifying the message type when setting up subscribers and publishers. This helps if you run this code before setting up your publishers. It also is required for codegen, if you're interested in that.
• It'll be more efficient to plot the location market once and then update its location in the figure, rather than clearing the figure each time and replotting.

-Cam