v0.1.

This repository serves as a tutorial on how to create a custom plugin for <point_cloud_transport>. It assumes that you have already gone through <point_cloud_transport> installation.

The first step in the process of implementing our new plugin is choosing its name. The name shouldn't be too long and should describe the plugin.

For example: <draco_point_cloud_transport> is a plugin which uses Google Draco compression, therefore the name draco.

For demonstrative purposes, the plugin which we will be implementing in this tutorial will be called goblin.

Over the course of this tutorial, we will modify a templateplugin plugin. To download the template to your local machine, enter the following commands in terminal:

$ cd point_cloud_transport_ws/src
$ git clone https://github.com/paplhjak/templateplugin_point_cloud_transport.git

This template uses the plugin name templateplugin, which is being refered to multiple times in the source files. The files and classes implemented within the plugin follow a strict naming convention, inheriting from the name of the plugin. To follow the convention, we will replace each instance of templateplugin with the name of our new plugin goblin. This can be done quickly using a case-sensitive find and replace tool. Most editors can invoke this tool by pressing CTRL+R. Once you make sure that the find is case-sensitive, go through all files in the project, and make the following replacements:

1. TEMPLATEPLUGIN -> GOBLIN
2. Templateplugin -> Goblin
3. templateplugin -> goblin

At the end of the tutorial, we will also rename files within the project to follow the convention.

Our new plugin will most likely use a custom message format to communicate. We will implement the message in msg/CustomMessage.msg file and change name of the file to suit our project. For example to GobMessage. Then we go through the following files:

1. templateplugin_publisher.h
2. templateplugin_subscriber.h
3. CMakeLists.txt
4. templateplugin_publisher.cpp
5. templateplugin_subscriber.cpp

and use the find and replace tool to replace the original name of CustomMessage with GobMessage.

CustomMessage -> GobMessage

Our plugin's publisher and subscriber can also make use of dynamic reconfiguration. If they do, we edit the ParameterGenerator appropriatelly in the following files:

1. cfg/Templateplugin_publisher.cfg
2. cfg/Templateplugin_subscriber.cfg

We can make use of the dynamic reconfiguration tutorial if necessary.

Implementation of the publisher can be located in src/templateplugin_publisher.cpp within function publish.

The publish function takes in a sensor_msgs::PointCloud2 message, which should be compressed and converted into our custom message format GobMessage. Once the message is ready, we pass it as an argument to publish_fn.

Implementation of the subscriber can be located in src/templateplugin_subscriber.cpp within function internalCallback.

The internalCallback function takes in our custom message format GobMessage, which should be decompressed and converted into sensor_msgs::PointCloud2. Once the point cloud message is ready, we pass a shared pointer to it as an argument to user_cb.

Before we distribute our plugin, it is important that we fill in all the necessary information about it.

In template_plugins.xml, make sure to provide brief description of both the publisher and the subscriber our plugin uses.

In package.xml, first change the description tag and maintainer tags. These are required and important tags because they let others know who to contact about the package.

At least one maintainer is required, but you can have many if you like. The name of the maintainer goes into the body of the tag, but there is also an email attribute that should be filled out.

Next fill in the license tag, which is also required. Finally fill in the dependencies tags.

The last required step is to rename files in the project. For this, replace any instances of Templateplugin with Goblin etc.

For example templateplugin_subscriber.cpp should be renamed to goblin_subscriber.cpp amd TemplatepluginPublisher.cfg should be renamed to GoblinPublisher.cfg .

At this point your plugin should be able to succesfully compile, build and be recognized by <point_cloud_transport>.

To see all plugins currently available at your system, enter command:

rosrun point_cloud_transport list_transports