rosbag recorded imu and image sampling intervals are not stable

[yaanggny]

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Description

When using Kalibr for IMU-camera calibration of ZED2i, there is a difference in rotation and translation compared to the given values. We compared the timestamps of the imu data and image data output by ROS and found that the sampling interval was unstable, with fluctuations reaching several milliseconds. However, the sample interval in the sample data provided by Kalibr is very stable, and I am not sure if this is the reason for the calibration failure.

Steps to Reproduce

1. build zed-ros-wrapper as README.
2. fix params/common.yaml and params/zed2i.yaml
3. roslaunch zed_wrapper zed2i.launch
4. rosbag record /zed2i/zed_node/left/image_rect_color /zed2i/zed_node/imu/data_raw

Expected Result

output sampling interval is stable or has a small fluctuation.

Actual Result

IMU sample intervals: (200Hz)

left cam image (rectified, @VGA， 15Hz) sample intervals:

---

IMU @200Hz

left cam image (rectified, @HD720, 30Hz) sample intervals:

ZED Camera model

ZED2i

Environment

OS: Ubuntu 20.04 
CPU: Intel i7-11850H
GPU: RTX A3000
ZED SDK: v4.1.2, v4.1.0, v3.8.x
ROS: Noetic

Anything else?

No response

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