You can find these installation instructions here.
sudo apt update
sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'
sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
sudo apt update
sudo apt install -y ros-melodic-desktop-full
echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
source ~/.bashrc
sudo apt install python-rosdep python-rosinstall python-rosinstall-generator python-wstool build-essential
sudo rosdep init
rosdep update
cd ~
sudo apt install -y git
git clone https://github.com/ArduPilot/ardupilot.git
cd ardupilot
git checkout Copter-3.6
git submodule update --init --recursive
sudo apt install -y python-matplotlib python-serial python-wxgtk3.0 python-wxtools python-lxml python-scipy python-opencv ccache gawk python-pip python-pexpect
sudo pip install -y future pymavlink MAVProxy
echo 'export PATH=$PATH:$HOME/ardupilot/Tools/autotest' >> ~/.bashrc
echo 'export PATH=/usr/lib/ccache:$PATH' >> ~/.bashrc
source ~/.bashrc
cd ~/ardupilot/ArduCopter
sim_vehicle.py -w
sudo sh -c 'echo "deb http://packages.osrfoundation.org/gazebo/ubuntu-stable `lsb_release -cs` main" > /etc/apt/sources.list.d/gazebo-stable.list'
wget http://packages.osrfoundation.org/gazebo.key -O - | sudo apt-key add -
sudo apt update
sudo apt install -y gazebo9 libgazebo9-dev
sudo apt upgrade libignition-math2
cd ~
git clone https://github.com/khancyr/ardupilot_gazebo.git
cd ardupilot_gazebo
git checkout dev
mkdir build
cd build
cmake ..
make -j4
sudo make install
echo 'source /usr/share/gazebo/setup.sh' >> ~/.bashrc
echo 'export GAZEBO_MODEL_PATH=~/ardupilot_gazebo/models' >> ~/.bashrc
sudo apt-get install -y ros-melodic-mavros
wget https://raw.githubusercontent.com/mavlink/mavros/master/mavros/scripts/install_geographiclib_datasets.sh
sudo chmod +x install_geographiclib_datasets.sh
sudo ./install_geographiclib_datasets.sh
mkdir catkin_ws
cd catkin_ws
mkdir -p src
cd src
catkin_init_workspace
echo "source ~/catkin_ws/devel/setup.bash" >> ~/.bashrc
cd ~/catkin_ws
catkin_make
source ~/catkin_ws/devel/setup.bash
Download the provided zip file in your Downloads folder
cd ~/Downloads
unzip InterIIT_DRDO.zip
mv prius_description interiit22 prius_msgs ~/catkin_ws/src/
cd ~/catkin_ws
sed -i '8 a \ \ <build_depend>prius_msgs</build_depend>' src/interiit22/package.xml
catkin_make
echo 'export GAZEBO_MODEL_PATH=$HOME/catkin_ws/src/MP_DR_T18/models' >> ~/.bashrc
Extract our package in ~/catkin_ws/src/ and then run
cd ~/catkin_ws
catkin_make
cd ~/catkin_ws/MP_DR_T18
pip -r requirements.txt
Launch the world
roslaunch MP_DR_T18 drdo_world1.launch
Start Ardupilot SITL
sim_vehicle.py -v ArduCopter -f gazebo-iris --console
Once SITL provides the 3D fix run the autopilot
rosrun MP_DR_T18 autopilot.py