Installing and running the Velodyne Height Map package on ROS Melodic distribution

The ROS Velodyne Height Map package (https://wiki.ros.org/velodyne_height_map) is a useful tool for identifying obstacles in a point cloud. An example of potential obstacles is shown below (the red squares).

However the last supported ROS distribution seems to be Indigo, a few releases from the latest Melodic distribution. But it is still possible to install and run the package on the latest ROS distribution. To do that, the source code from https://github.com/jack-oquin/velodyne_height_map must be downloaded and compiled on the ROS installation. The following steps illustrate the procedure.

Create a ROS Catkin workspace

1. Follow the tutorial here at https://wiki.ros.org/catkin/Tutorials/create_a_workspace to create an empty workspace, e.g /path/to/catkin_ws/.

Download the Velodyne Height Map source code

1. Open up a Terminal. Change the directory to the location of the Catkin workspace's src directory created earlier.
   
   $ cd /path/to/catkin_ws/src
   
2.  Assuming git is installed, clone the velodyne height map source code.
   
   $ git clone https://github.com/jack-oquin/velodyne_height_map.git

Build the package

1. In the Terminal, change the directory to the root of the Catkin workspace.
   
   $ cd /path/to/catkin_ws
2. Type in the following command to build the packages.
   
   $ catkin_make

Once the package is built, the Velodyne Height Map package can be executed according to the instructions here at https://wiki.ros.org/velodyne_height_map. For example,

$ rosrun velodyne_height_map heightmap_node