Ubuntu 20.04 and CI Dockerfiles

[goldbattle]

This is a PR of the ori-drs/kalibr repo which has fixes for 20.04 and python3. As mentioned in #405 (comment) I forked and am willing to handle review comments to make this mergeable. I have additionally added Docker files and a CI github action to build the Docker files to ensure that the codebase builds on all platforms (ubuntu 16.04 kinetic, 18.04 melodic, 20.04 noetic). There were some modifications I needed to perform from the ori-drs repo to ensure that everything still built with python2.

I have tested performing camera calibration, and camera to IMU calibration with the sample datasets. One can see the github action CI builds here. The goldbattle/kalibr Readme has instructions on how to build and use the docker.

A short summary of changes:

• 20.04 and python3 support from https://github.com/ori-drs/kalibr
• Single camera mutial observation error fix from Cameras are not connected through mutual observations #364
• Docker files for ubuntu 16.04 kinetic, 18.04 melodic, 20.04 noetic
• Small fix to export results into the same folder as the bag file

The readme will likely need some small changes along with the wiki (or just add example build instructions to the readme).

[goldbattle]

Docker instructions to be added to the wiki:

First make sure that you have install docker on your system using the official Docker Get Docker guide.
We can then build the docker container using:

cd <workspace>/src/kalibr
docker build -t kalibr -f Dockerfile_ros1_20_04 .

Then after building we can first download an example dataset and then perform following to calibrate.

cd <workspace>
mkdir example && cd example
wget http://robotics.ethz.ch/~asl-datasets/ijrr_euroc_mav_dataset/calibration_datasets/cam_april/april_6x6.yaml
wget http://robotics.ethz.ch/~asl-datasets/ijrr_euroc_mav_dataset/calibration_datasets/cam_april/cam_april.bag

We can now mount the data folder in the container /data path and enter the command prompt.
Some more details can be found on the ROS wiki for Docker.

FOLDER=$(pwd)
xhost +local:root
docker run -it -e "DISPLAY" -e "QT_X11_NO_MITSHM=1" \
    -v "/tmp/.X11-unix:/tmp/.X11-unix:rw" \
    -v "$FOLDER:/data" \
    kalibr
source devel/setup.bash
rosrun kalibr kalibr_calibrate_cameras \
    --bag /data/cam_april.bag --target /data/april_6x6.yaml \
    --models pinhole-radtan pinhole-radtan \
    --topics /cam0/image_raw /cam1/image_raw