Project -- Slam with Lidar + IMU + encoder
===
#### Refer to: https://zhuanlan.zhihu.com/p/415830550

Description
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##### Our system combined with two wheel encoders, imu with 6 DoF and a 2D lidar. First we apply a kalman filter on imu and encoder odometry, and combined this result with lidar mapping using gmapping algorithm.
Components
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##### Raspberry Pi 4B: Combine all sensor data, include some sensors preprocessed on Pi pico.
##### Pi Pico: Read and process encoder data in higher speed compared to RPi, receive control from RPi.
##### Sensors: 2D lidar, encoders, imu
##### Circuit components: motor driver, DC-DC convertor, switch

Raspberry Pi ROS setup
===
##### Boot the image file into sd card by dd. You can check progressing rate:
$ sudo killall -29 dd
##### Recover apt-update
$ sudo apt-get -y update --allow-releaseinfo-change

#### As for initial setup, the usr is pi, and the password is raspberry.

#### Refer to: http://sar-lab.net/teaching/ros-images-for-raspberry-pi/
Start VNC screen
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$ sudo systemctl start lightdm
$ sudo touch ~/system_start.sh
$ sudo echo "sudo systemctl start lightdm" >> /home/pi/system_start.sh
#### Add line /home/pi/system_start.sh to file "/etc/rc.local" before "exit 0".
$ chomod +x /home/pi/system_start.sh
#### Now it can run when you boot.
Keyboard tool
---
$ pip install git+https://github.com/li-rupert/getkey@adding-osx-tests

Setup ROS
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#### Refer to: https://ithelp.ithome.com.tw/articles/10203126
$ mkdir catkin_ws
$ cd catkin_ws
$ catkin_make
$ echo "source /home/user/catkin_ws/devel/setup.bash" >> ~/.bashrc
#### If we want to make the package specifically.
$ catkin_make --only-pkg-with-deps <target_package>
#### And remember to change back the setting.
$ catkin_make -DCATKIN_WHITELIST_PACKAGES=""
#### Or you can done by this.
$ catkin_make --pkg <my_package_name>
Setup Wire Communication
---
### i2c

#### Refer to: https://blog.gtwang.org/iot/raspberry-pi-mpu6050-six-axis-gyro-accelerometer-1/
##### First raspi-config i2c. Then test by follow.
$ sudo apt-get install i2c-tools
$ sudo i2cdetect -y 1
$ sudo modprobe i2c-dev
$ sudo chmod 666 /dev/i2c-*
##### You should be able to see your device in one of the addresses.
##### Install C++ library for i2c.
$ sudo apt-get install libi2c-dev
##### See also example for mpu6050: https://github.com/richardghirst/PiBits.git

Setup RPlidar
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#### Refer to: https://www.ncnynl.com/archives/201611/1100.html

$ cd catkin_ws/src
$ git clone https://github.com/ncnynl/rplidar_ros.git

##### Plug in USB port and check permission, and enable permission.
$ ls -l /dev |grep ttyUSB
$ sudo chmod 666 /dev/ttyUSB0
##### Set catkin_make.
$ cd ~/catkin_ws
$ catkin_make
##### Test code in rviz.
$ roslaunch rplidar_ros view_rplidar.launch
ROS ekf package
---
#### Refer to: https://blog.csdn.net/qcxyliyong/article/details/103708496

#### Install orocos-bfl
$ cd ~/
$ mkdir /source_code_ws
$ cd /source_code_ws
$ git clone https://github.com/jyLeo/orocos-bfl.git
$ cd orocos-bfl
$ mkdir build
$ cd build
$ export CMAKE_INCLUDE_PATH=/home/pi/source_code_ws/orocos-bfl/path/to/installed/library/include
$ export CMAKE_LIBRARY_PATH=/home/pi/source_code_ws/orocos-bfl/path/to/installed/library/lib
$ cmake ..
$ make
$ sudo make install
#### Install robot_pose_ekf
$ cd ~/catkin_ws/src
$ git clone https://github.com/ros-planning/robot_pose_ekf.git
$ cd ..
$ catkin_make

#### Reference:
##### Wheel odometry: https://wiki.ros.org/navigation/Tutorials/RobotSetup/Odom

GMapping
---
#### Refer to: http://wiki.ros.org/gmapping?distro=jade
#### and: https://automaticaddison.com/how-to-set-up-the-ros-navigation-stack-on-a-robot/
#### and: https://www.796t.com/content/1552905625.html

$ sudo apt-get install libbullet-dev
$ sudo apt-get install libsdl1.2-dev

#### Some need melodic devel. If you get the wrong devel version, there may be some package missing.
$ cd catkin_ws/src
$ git clone https://github.com/ros-perception/openslam_gmapping.git
$ git clone https://github.com/ros-perception/slam_gmapping.git
$ git clone --single-branch --branch melodic-dev https://github.com/ros-planning/navigation.git
$ git clone --single-branch --branch melodic-dev https://github.com/ros/geometry2.git
$ git clone https://github.com/ros-planning/navigation_msgs.git
$ cd ..
$ catkin_make

#### Refer to: https://pse.is/474yav
#### GMapping explanation: https://www.guyuehome.com/14967

ROS tf
---
#### The tf tree composed of frame and it's child frame, a frame can have only one mother frame, but multiple child frames.
#### Save tf tree as pdf file.
$ rosrun tf view_frames
Pi Pico Setup
===