sync_and_detect for multi-cameras

[Jan Li]

Hi Dr. Bernd Pfrommer:

I have some problems about sync_and_detect node: 

1. Dose the sync_and_detect node can sync images from multi-cameras and detetect tags,  pub detected tags as well?

2. It doesn’t work when I add two image topics to the roslaunch file, should i set other params?

3. would it become very slow when detecting muliti-imags?

Looking forward to your reply.

Best wishes!

[Bernd Pfrommer]

1. Yes

2. "It doesn't work" is insufficient information. How about error logs? Is sync_and_detect subscribing to the right topics? Use rosnode info to check.

3. sync_and_detect's CPU consumption will scale linearly with the number of images

[Jan Li]

As for problem 2：

The image topics are /cam0/image_raw and /cam1/image_raw, but no detected tags message, it seems like no synced message from  flex_sync...

[Bernd Pfrommer]

Are the cameras really hardware synced? The way you configured your launch file, the images must have identical header time stamps. Set use_approximate_sync to true and see what happens.

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[Jan Li]

Oh, I made the mistake, the cameras are not hardware synced...I run the use_approximate_sync_ node to make identical header time stamps of two image topics, and then run sync_and_detect _node, it works!

I appreciate your help very much!!!

[Hongbo Zhu]

Hi, I am very interested in multi-camera extrinsic calibration by using TagSLAM. But I still cannot figure out how to use multiple cameras with sync_and_detect.launch. Would you mind share your camera.yaml and tag_slam.yaml? Thanks!

[Bernd Pfrommer]

The files camera.yaml and tag_slam.yaml don't even come into the picture when using sync_and_detect. Can you describe more precisely what the problem is? No output? Error message?

Things to check: what topics is sync_and_detect subscribing to (use rosnode info)? What are the topic names published by your camera driver? Do they match? Are your cameras hardware synced? If not, see answer above.

[Hongbo Zhu]

Thanks for your reply! I have fixed the problem. It is all about the hard syncronization of my cameras. Thanks!