Getting the data from the rosbag msg, when the data is an array

I can read data from my bag files, which works and I can plot the data

filepath = '/home/bren/rosbag/data/2019-03-21-17-06-24.bag'
bag = rosbag(filepath);
motors = select(bag, 'Topic', '/pennybot/motors');
update_ms = timeseries(motors,'UpdateDurationMs');
set_ms = timeseries(motors,'SetVelDurationMs');

But I can't figure out how to read from an array. I've tried a number of ways, but none work, for example:

rpm_l = timeseries(motors,'Rpm[1]');

This is the msg:

Header header

string[] name

# Feedback from the motors
float64[] rpm

# feedback from the controller
float64[] desired_rpm

float64 update_duration_ms
float64 set_vel_duration_ms
bool motor_error

I'm also can't read the motor_error, does matlab support. When I use the rosmsg info, it says the motor_error is 'logical MotorError'. So is there away to plot this boolean?

Answer 1

[Cam Salzberger]

Hello Bren,

Rather than using timeseries, try using readMessages to extract messages from your rosbag selection object. Try it with both "DataFormat", "struct" and without if you are having issues with that as well.

-Cam

Answer 2

[Bren Pierce]

Perfect, thanks you Cam

For people that might find this msg this code worked for me.

bagselect = rosbag(filepath);

motors = select(bagselect,'Time',[bagselect.StartTime bagselect.StartTime + 1],'Topic','/pennybot/motors');

motorsMsgs = readMessages(motors);

motorsMsgs{0}.Rpm