Add ROS2 support

[shrijitsingh99]

Ported over the entire code to ROS2
Major changes:

• Renamed service to be compliant with ROS2 service naming standard
• Update RViz config for RViz2
• Use MultiThreadedExecutor with callback groups to achieve what the async spinner did
• Move some of the includes out 'dlio.h' to remove 'rclcpp' and other library dependencies on gicp
• Update launch and param files

[kennyjchen]

Awesome -- thanks @shrijitsingh99 for porting DLIO to ROS2, it looks great! I've gone ahead and changed the base branch to feature/ros2. Thanks for the contribution :^)

[juliangaal]

Have you considered the changes to the sensor / lidar frame when working with Ouster data? @shrijitsingh99

Some recent discussions about it here: ouster-lidar/ouster-ros#33

[shrijitsingh99]

I don't think any changes are needed here.
From the discussion my understanding is that the data is by default published in sensor frame which the default extrinsics in the yaml reflect. If some user changes the frames they would need to update the extrinsic in the config file here.

The frame_id in the point cloud message itself doesn't affect the algorithm.

[yashmewada9618]

System: Ubuntu 22
ROS Version: Humble

Hello,
I used DLIO's ROS Noetic version, and it worked perfectly in the first run. However, when I converted the same bag file to ROS 2, things did not work out. After initializing the node, it worked for a short while, but as soon as the robot started moving, the pose estimation got messed up which I think is due to IMU's integration and pose estimation. The local maps from DLIO started moving in the Z direction instead of the correct forward motion. I tried changing the frames (as the Ouster lidar frame and sensor frames are rotated by 180 degrees), and calibration time, but it did not help. I noticed a notable change when I modified the gravity bias from 9.8 to -9.8 in the config file, where the pose estimation translated correctly, but the orientation was wrong.
Has anyone else experienced this issue with the ros2 branch of this code?

Thanks.