How to get an array from a Rosbag

2 次查看（过去 30 天）
Paolino De Risi
Paolino De Risi 2021-9-16
评论： Cam Salzberger 2021-9-17
Hi, I'm trying to plot a data from a rosbag, here what i did until now:
bag=rosbag('/home/paolino/bagfiles/subset.bag');
wh_gaz=select(bag,'Topic','/joint_states');
wh_gazStruct=readMessages(wh_gaz,'DataFormat','struct');
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?

请先登录，再回答此问题。

回答（1 个）

Cam Salzberger
Cam Salzberger 2021-9-16
I provided some guidance and sample code to a similar question here. That should help get you moving in the right direction!
-Cam
  2 个评论
Paolino De Risi
Paolino De Risi 2021-9-17
编辑：Paolino De Risi 2021-9-17
It doesn't work for me, in my case the record .Velocity has two elements inside since it is a float64 array with two elements. they are not indexed as subrecords as in the following image:
This seems not work:
function [wh1, wh2] = getwheelsvelocities(msg)
% Extract internal message first for efficiency
% (matters more for more nested messages)
wh_vect = msg.Velocity(1);
wh_vect1=msg.Velocity(2);
wh1 = wh_vect;
wh2 = wh_vect1;
end
Cam Salzberger
Cam Salzberger 2021-9-17
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];
end
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.
-Cam

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 ROS Log Files and Transformations 的更多信息

标签

产品


版本

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by