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Two subscriber topics in rclpy.spin() not working properly and losing frames. [closed]

asked 2021-08-18 11:02:23 -0500

NiranjanRavi gravatar image


I am working with ROS2 - foxy distribution. I have two usb cams, generate frames at 30 fps.
USB cam packages are from this git: . When i run the publishers, i could see the topic listed as, /usb_cam_0/camera_info , /usb_cam_0/image_raw , /usb_cam_1/camera_info, /usb_cam_1/image_raw .

I want to subscribe a frame from camera 1 and concat it with frame from camera 2 and save in a directory. Then the cycle repeats as long as code runs. I wanted t code in python. For some reason, message filters/time synchronizer library in python was throwing error which i wasn't able to fix. (

So the approach which I tried:

rclpy.spin() which has below functions:

self.subscription_1 = self.create_subscription(Image, '/usb_cam_0/image_raw', self.camera_0_callback, 1) self.subscription_2 = self.create_subscription(Image, '/usb_cam_1/image_raw', self.camera_1_callback, 1)

camera_0_callback is not getting called always. Almost half of times when the code runs, it skips camera_0_callback. I tried variable delays, increasing queue sizes but it doesn't seem to work.

All the while, ros2 topic list shows the topics; Could it be an issue with camera? Or am i not performing the queue logic incorrectly? Any inputs will be helpful.

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Closed for the following reason the question is answered, right answer was accepted by NiranjanRavi
close date 2021-09-20 17:01:49.827827

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answered 2021-08-19 20:22:43 -0500

Pepis gravatar image

Are you using a single threaded or a multi threaded executor? If its the case try a multi threaded executor. Could you share your code to see how are you handling the node spin?

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Hi, I had to do a work around. Saving individually and concat later. It reduces the frame loss considerably.

NiranjanRavi gravatar image NiranjanRavi  ( 2021-09-20 16:57:49 -0500 )edit

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Asked: 2021-08-18 11:02:23 -0500

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Last updated: Aug 19 '21