Parse String Data ROS topic in Simulink

Hi to all,

I would like to be able to read my /mobile_robot/io topic which has this output:

data: 1517480481.375425333,0,0,0,0,1514,3307,0,0,0,0,0,0,0,0,0,1,1,0,1,0,1,1,0,0,0,0,0,0,0,0,6629
---
data: 1517480481.476979162,0,0,0,0,1032,3571,0,0,0,0,0,0,0,0,0,0,1,0,1,1,1,1,0,0,0,0,0,0,0,0,6630
---
data: 1517480481.574876785,0,0,0,0,288,3308,0,0,0,0,0,0,0,0,0,0,1,0,1,1,1,1,0,0,0,0,0,0,0,0,6631
---
data: 1517480481.674732409,0,0,0,0,4914,3268,0,0,0,0,0,0,0,0,0,1,1,0,1,1,1,1,0,0,0,0,0,0,0,0,6632

I would like to read the first value which is the timestamp and the values placed at positions 6 and 7. The message type is String and I'm not able to correctly parse the output of this node.

I created the subscription block in Simulink and then I added the BUS Selector with three outputs:

Data
Data_SL_Info.CurrentLength
Data_SL_Info.ReceivedLength

What kind of block or function do I need to use in order to be able to read the timestamp and values at 6 and 7 columns?

I hope you can help me!

[marcusbarnet]

Is it possible to call a Matlab function to load the data?

In my Matlab, I use this code to obtain the same data:

bagselect_io = select(bag, 'Topic', '/robo/io');
readMsg_io = readMessages(bagselect_io);
io_data = zeros(size(readMsg_io,1),32);

for i = 1:size(readMsg_io,1)
    C = strsplit(readMsg_io{i,1}.Data,',');
    io_data(i,:) = str2double(C);
end

External Current Sensor %%%

curr_sensors_time = io_data(:,1) - io_data(1,1);
curr_sensors_time(elements:end,:,:)=[];

currTmp = io_data(:,6:7) - 2410; % current data from the external sensors
currTmp = [ currTmp(:,1), currTmp(:,2); ]; 
curr_sensors = -(currTmp)*(300/5000)*0.5*0.92;
curr_sensors(elements:end,:,:)=[];

cuurent_sensor_data = [curr_sensors_time, curr_sensors(:,1), curr_sensors(:,2)];

I can't use it inside Simulink, unfortunately.

Answer 1

[Sebastian Castro]

You can use a MATLAB Function block to read the message.

If you pass in the signal "Msg", it will appear in the MATLAB Function block as a structure. For example, you should be able to do:

function readMyData(msg)

    numElements = msg.Data_SL_Info.ReceivedLength;
    for idx = 1:numElements
        some_value = msg.Data(idx);
        % ... and then you do something with these values
    end

end