Clarification about the input synchronization step

Posted by 1fabrism on
URL: http://official-rtab-map-forum.206.s1.nabble.com/Clarification-about-the-input-synchronization-step-tp5841.html

Hello, I have a question about how exactly RTAB-Map synchronizes the input topics camera images and odometry.

My Setup:
I have a RealSense camera which I already set to sync the color and depth images (as well as camera info) when publishing them on their respective ROS topics. Then I have an EKF from the robot_localization ROS package that fuses wheel encoders with IMU and visual odometry to produce a filtered odometry. This is what goes into RTAB-Map.

I looked into how ROS syncs topics, with the ExactTime or ApproxTime policies, and I was wondering if this is what is controlled by RTAB-Map's "ApproxSync" parameter? If I set this to "False", will RTAB-Map only create a node if and only if the camera and odometry topics have the same nanosecond-precision timestamp? Or does that parameter just control the synchronization of the camera images?
Basically, what I want to know more about is how does RTAB-Map sync odometry with camera images. How does it ensure that the data points from the two topics were taken at the same time?

Thanks in advance.