RRT-ROS

This is an implementation of Rapidly-exploring Random Tree (RRT) algorithms in C++ for ROS Melodic. There are ROS nodes for loading and parsing a map image file (JPG/PNG/PGM), planning a path to the goal using RRT, visualizing the map and the built RRT, and an interface for drawing a custom map that can be exported as a JPG file or published directly.

Nodes and Topics

Packages

• nav_msgs: Contains the Message Description Specifications for this project.
• rrt_planner: Implements the RRT algorithms. Contains planner_node and pathrequest_node.
• rrtplanner_map: Provides the interfaces for serving and visualizing the maps, and drawing custom maps. Contains visualizer_node, mapserver_node and mapdrawer_node.

Table of Contents

• RRT-ROS
  • Nodes and Topics
  • Packages
• Table of Contents
• Prerequisites
• Build Guide
• How to Run
  • Setup
  • Nodes
  • Start RRT algorithm
  • Visualizer
  • Map Drawer
• Gallery
• References

Prerequisites

• Ubuntu 18.04 LTS
• ROS Melodic (Required Packages)
  • OpenCV 3.2.0
    • OpenCV Release
    • OpenCV Contrib Release

Build Guide

Clone this repository.

> git clone https://github.com/djtfoo/rrt-ros
> cd rrt-ros

Use catkin build to build the ROS project.

> catkin build

When building for the first time, the following error would occur. Run catkin build again to build the packages.

If the build is successful, you should see the following packages generated:

How to Run

Setup

Launch roscore in a terminal:

roscore

In each new terminal, source for the local setup file:

> cd rrt-ros
> source devel/setup.bash

---

Nodes

First, run planner_node:

rosrun rrt_planner planner_node

Optionally, run visualizer_node in a new terminal to show a GUI interface to configure the navigation parameters and visualize the tree building on the map:

rosrun rrtplanner_map visualizer_node

Run mapserver_node in a new terminal to load a map image file, generate the occupancy grid from the image, and publish it to the /map topic for the planner and visualizer:

rosrun rrtplanner_map mapserver_node <path_to_map_image> <gridsize>

• path_to_map_image: the file path (relative or absolute) to the map image file. The image should be PNG/JPG/PGM.
• gridsize: the size in pixels of the occupancy grid.

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Start RRT algorithm

If using visualizer_node, the user can select the start and goal positions using the interface, and select the RRT algorithm to use.

Otherwise, run pathrequest_node in an open terminal to provide the start and goal positions to start the RRT search:

rosrun rrt_planner pathrequest_node <start_x> <start_y> <goal_x> <goal_y> <rrt_ver>

• start_[xy]: the pixel coordinates of the start position.
• goal_[xy]: the pixel coordinates of the goal position.
• rrt_ver: 0 for basic RRT, 1 for RRT*.

The start and goal positions cannot be an obstacle and is checked by planner_node.

Output

The RRT planner begins to build the RRT, with a 5% bias towards sampling the goal state. The vertices (nodes) of the RRT are published to the /rrtnode topic as they are generated. If a path is found, it will be printed to the terminal and published to the /path topic.

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Visualizer

The visualizer_node subscribes to all of the topics and displays and updates a view of the map with the built RRT and the start and goal positions.

How to Use:

• Run visualizer_node with rosrun.
• Publish an occupancy grid map (e.g. with mapserver_node or mapdrawer_node) for visualizer_node to open a window displaying the map.
• Click with the left mouse button to set a start position.
• Click with the right mouse button to set a goal position.
• Click any of the "Plan Path" buttons to publish a path request using the respective RRT algorithm after setting a start and goal position.
• The visualizer will display the RRT while it gets built by the planner. If a path from the start to the goal is found, it will be highlighted in yellow.
• After the RRT planning has completed, start and goal positions can be set and a "Plan Path" request can be published again, or a new occupany grid map can be published to open a new map window.

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Map Drawer

Custom maps can be drawn using the mapdrawer_node. The custom map can then be exported as an image file to "./maps/custom.jpg", or have its occupancy grid data published directly to the /maps topic.

When choosing to publish directly, the planner_node and visualizer_node (if wanting visualization) should already be running before publishing the data.

Parameters can optionally be provided to change the map size and occupancy grid size (if publishing directly). To run the map drawer:

rosrun rrtplanner_map mapdrawer_node <map_width> <map_height> <gridsize>

• map_width: the width of the map in pixels. The default value is 500.
• map_height: the height of the map in pixels. The default value is 500.
• gridsize: the size in pixels of the occupancy grid. The default value is 5.

How to Use:

• Click and drag with the left mouse button to draw obstacles (in white).
• Click and drag with the right mouse button to erase drawn obstacles.
• Click "Publish Map" to generate the occupancy grid and publish it to the /map topic. This node will shutdown and exit afterwards.
• Click "Export Map" to save the drawn map to a JPG file. This node will shutdown and exit afterwards.

Gallery

Basic RRT algorithm

RRT* algorithm

Visualizer

Map Drawer

References

• Steven M. Lavalle’s RRT web page
• Original Lavalle et al. RRT paper
• Wikipedia page on RRT
• RRT* Brief Explanation (YouTube)