How to get an array from a Rosbag

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Paolino De Risi
Paolino De Risi on 16 Sep 2021
Commented: Cam Salzberger on 17 Sep 2021
Hi, I'm trying to plot a data from a rosbag, here what i did until now:
This struct is a 19153x1 cell and each element is a 1x1 struct with a velocity record, a 2x1 array.
Now, what i need is to create 1 column array with each wh_gazStruct.Velocity first element, but I can't find a solution. Until now I tryed:
wh_gaz_mat=cellfun(@(m) double(m.Velocity),wh_gazStruct);
but since the .Velocity record has two elements it doesn't work. How may I solve my problem?

Answers (1)

Cam Salzberger
Cam Salzberger on 16 Sep 2021
I provided some guidance and sample code to a similar question here. That should help get you moving in the right direction!
Cam Salzberger
Cam Salzberger on 17 Sep 2021
Well, I don't know exactly what your messages look like. But if I set up my messages like this (to simulate using readMessages with DataFormat='struct'):
msg = rosmessage('sensor_msgs/JointState', 'DataFormat', 'struct');
n = 4;
msgs = cell(n, 1);
for k = 1:n
msgs{k} = msg;
msgs{k}.Velocity = [k ; -k];
Then I can do this:
[wh1, wh2] = cellfun(@getwheelsvelocities, msgs);
with your code as-provided, and it works just fine.
If you have any messages that do not have two entries in the Velocity field, then this code will fail.

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