camera time stamp synchronizer

ROS2 package to synchronize time stamps of two hardware-synchronized cameras by using the "ApproximateTimeSynchronizer" from ROS2's message_filters.

Use this package if you have a hardware synchronized stereo camera and want to force the ROS header time stamps of the image messages coming from the cameras to be identical. The node subscribes to two image topics and re-publishes them but with aligned (identical) time stamps.

For efficiency reasons this node should be run in the same address space as the other nodes, thereby avoiding a copy of the image content. You can find a sample launch script in the flir_spinnaker_ros2 repository.

CAUTIONS:

1. The time stamp adjustment is done by a bad hack: casting away the constness of a shared pointer to an image, and adjusting the time stamps. So far this has worked as tested and it does not seem to throw off ROS's approximate sync algorithm, but if some nodes rely on the original time stamp of the published image to stay constant there may be adverse side effects to running this node.

2. ROS's approximate time sync algorithm will work reasonably well so long as there is no severe CPU load on the host. If one of the camera drivers is slow to process or even drops frames, then there is no guarantee that images with the same time stamp will actually correspond to the same hardware sync pulse.

How to build

Make sure you have your ROS2 environment sourced, e.g:

source /opt/ros/galactic/setup.bash

Create a workspace (cam_sync_ros2) and clone this repo:

mkdir -p ~/cam_sync_ros2/src
cd ~/cam_sync_ros2
git clone https://github.com/berndpfrommer/cam_sync_ros2 src/cam_sync_ros2

Build the node and source the workspace:

colcon build --symlink-install --cmake-args -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
. install/setup.bash

License

This software is issued under the Apache License Version 2.0.