Overview

This repo was used a way to get some more experience with the ROS velodyne drivers and ROS in general. The objectives highlighted below were originally a part of a coding challenge. At the time, I did not have the skill set to complete in the alotted 12 hours. I am now much more comfortable in the ROS environment, and wanted to prove to myself that I complete the challenge with ease.

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Objectives

Given the .bag file of recorded ROS topics, create three runnable ROS nodes that do the following:

1. Remove 2 channels of signals from the 16 channels of the Velodyne VLP16
2. Remove noise in the remaining point cloud
3. Detect upright line structures in the point cloud and visualize them in colors.

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Implementation Overview

Channel Removal

The initial method is definitely a little over the top, but I wanted to fully understand the sensor_msgs/PointCloud2 topic type. Most of the functionality lays within the callback function downsample. Every time a message is received , a outgoing point cloud message is created, and all the necessary fields are set (such as header, timestamp etc). The point cloud modifier sets the necessary data fields (X, Y, Z, Intensity and Ring #) in the point cloud. Iterators are instantiated that allowed me to loop through the points present in each message, and if they don't belong to either beam 1 or beam 2, they are pushed into the new point cloud. Afterwards, the point cloud is then published.

Noise/Outlier Removal

In this node, we subscribe to the published point cloud from the Channel Removal node. We then convert this sensor_msgs::PointCloud2 type to a pcl point cloud, and apply a voxel grid filter to it. This is then converted back out to a sensor_msgs::PointCloud2 and published on a topic.

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Downloading/Building

cd /your/catkin_ws/src/

Once you're in the right directory, clone this repo using the command below.

git clone https://github.com/aidanjones3/VelodyneROS_Exploration.git

The repo can be built by running the following command in your catkin_ws

catkin_make

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Running the ROS Nodes

The ROS nodes can be run indiviually, as long as you have a topic with sensor_msgs/PointCloud2 being published to it. The three seperate nodes can be ran with the commands below:

rosrun velodyne_test velodyne_test _topic_name:="\velodyne_points"

rosrun velodyne_test outlier_removal _topic_name:="\velodyne_points"

rosrun velodyne_test objec_segmentation _topic_name:="\velodyne_points"

Obviously, you can substitute the topic name of velodyne_points with the topic name you wish to subscribe to.