Using matplotlib in a ros node in docker

edit

Hello,

I am running a ros node (melodic) inside docker with python3, and I am having trouble with matplotlib.

tl;dr: I cannot get the TkAgg backend for matplotlib to work inside the rosnode. Switching to the Agg backend avoids an error but does not display the plot.

More details / what I have tried:

My node subscribes to several topics, does some processing on them, and then updates a plot with the values. It is similar to the accepted answer in https://answers.ros.org/question/2647....

My first attempt I used import matplotlib.pyplot as plt and after creating the plot called plt.show(). The opened the plot window, but later when I tried to use plt.draw() and plt.pause(0.00000000001) to update nothing happened.

I though it must be because the show command is blocking, so I tried changing it to plt.show(block=False). However, this gave me the following error:

[ERROR] [1579336272.270732, 1573680615.824510]: bad callback: <bound method plot_6dof.ado_pose_gt_cb of <__main__.plot_6dof object at 0x7ff551d299b0>>
Traceback (most recent call last):
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rospy/topics.py", line 750, in _invoke_callback cb(msg)
  File "/root/msl_raptor_ws/src/msl_raptor/src/viz_tools/plot_6dof.py", line 78, in ado_pose_gt_cb self.update_plot()
  File "/root/msl_raptor_ws/src/msl_raptor/src/viz_tools/plot_6dof.py", line 150, in update_plot plt.pause(0.0000001)
  File "/usr/local/lib/python3.6/dist-packages/matplotlib/pyplot.py", line 295, in pause show(block=False)
  File "/usr/local/lib/python3.6/dist-packages/matplotlib/pyplot.py", line 253, in show return _show(*args, **kw)
  File "/usr/local/lib/python3.6/dist-packages/matplotlib/backend_bases.py", line 192, in show manager.show()
  File "/usr/local/lib/python3.6/dist-packages/matplotlib/backends/_backend_tk.py", line 551, in show ile "/usr/lib/python3.6/tkinter/__init__.py", line 1788, in wm_attributes return self.tk.call(args)
RuntimeError: main thread is not in main loop

After some googling I came across a link about using matplotlib in a virtualenv https://www.pyimagesearch.com/2015/08... and I thought I had the answer. I changed my backend to Agg, and this did mean I stopped getting the error but no plot ever appears (for plt.show() or plt.show(block=False)).

When using the bash in the container, I tried a quick test of running the python3 interpreter, importing matplotlib.pyplot as plt and making a simple plot. Using the TkAgg backend I can display a plot with blocking or without. Using the Agg backend I cannot get any plot to display.

Thanks in advance for the help!