Robotics Assessment #I Solution



1 Overview

This assessment will evaluate your ability to perform path planning and localisation. It aims to evaluate the following two learning outcomes:

• Familiarity with Path planning algorithms.

• Ability to implement robot localisation.

• Integrate with RViz to visualise your robot in the world.

• Good ROS programming practices.

Yourrobot willoperate within thestagesimulator,whichcanberunusingthecommand rosrun stage_ros stageros ‘rospack find stage_ros‘/world/ to use the willow-erratic map. A different map is provided below.

2 Practicalities

The due date for this assessment is 5pm on Friday the 28th of October. Handing in up to 24 hours late will incur a 10% penalty, while handing in up to 7 days late will incur a 25% penalty. After that, you will receive

0 for the assessment.

Please be aware of the University’s policy on Plagiarism, ensure that all work is your own, and that any sources you use are acknowledged. Additionally, please make sure that all source code you hand in follows programming best practices and is well documented.

This assessment will count for 55% of your overall course mark. You may work in teams of 2, or individually. If you work in a team, please include a short text file describing who did what in the project. You may also tell me if you feel your partner is not pulling their weight. If you work individually, you will gain an automatic 10% bonus to your final mark.

3 Preliminaries

1. You will need to install the map server ( sudo apt-get install ros-indigo-map-server for indigo, or ros-kinetic-map-server for kinetic).

2. Please download the zip file from the assessment page on myAberdeen which contains

• A .world file (for stage)

• A map image file (map.png)

• A .yaml file for the map server

•Apython node( This node publishes a topic, /noisy base scan which you will need to use instead of /base scan in your code.

• A launch file (r.launch).

3. The r.launch file will start up ROS, the map server a static transform and stage using the appropriate map (assuming you put everything in the /home/viki directory, otherwise, please edit the yaml file).

4. The static transformcreates a/map frame which can be used in RViz. If you prefer, you can edit the launch file to use fake localization as per practical 3.

5. Start up RViz (just type rviz) and play around with it. For example, try to add the map to the display, as well as the various frames of reference. To do this, choose ”Add” on the left hand part of the window and choose the appropriate item. You may need to type in the correct frame/topic to make this work.

4 Tasks

4.1 Task 1

ImplementaROSnodethatsubscribes to/base pose ground truth and broadcasts a transform as a child of the /map frame called /real robot pose. Then use this information to create a marker on the RViz window, displaying the robot’s true location and orientation. You should also display the robot’s pose, as obtained from odometry information, within RViz, enabling me to see the difference between where the robot is, and where it believes it is.

4.2 Task 2

The main aim of this assessment is to have your robot visit various points in the world. The only problem is that it’s going to have been kidnapped at the start…

Theaimofthistask istoperformrobot localisation. Youmayimplementeither aEKF orparticle filter based localisation algorithmto address this task, orutilise an existing library. The task willbedeemed successful when the robot goesto astartpoint, asgivenby the parameter/start pos (passed as a list [x, y]). You should create a marker when the robot reaches the start, as we will need to measure the distance between the actual start and where it thinks it is.

Alternatively,youcanchoosetosolveanon-kidnappedversionoftheproblem, inwhichcaseyoushould readtheparameterrobot start which will be passed as a [x, y, θ] triple.

4.3 Task 3

Yourrobot willbepassed asequenceof6points fromthe parameterserver, p1, p6, again passed as a list. From the start position, your robot must visit these 6 points (in any order you choose). Additionally, you must display these 6 points and the path you choose to follow on RViz, and also display the path your robot actually followed (using what you implemented in Task 1). Markers need to be dropped at each location by your robot.

Youmayalsoprefertodothistaskwithnoodometric noise(i.e.,ifyouhaven’t hadmuchluckwithtask


As an extra challenge, you may wish to implement a local obstacle avoidance algorithm to avoid obstacles

detected but not shown on the map you’ve been given.

5 Marking

Marking of this assessment will take place in the practicals of Monday the 7th and Tuesday the 8th of

November. You will receive 20 marks for achieving Task 1.

Achieving Task 2 will give you 20 marks if you utilise existing ROS stacks, or 30 marks if you implement the localisation yourself. Achieving this task with a known initial starting pose will reduce the marks you receive by 10.

Task 3isworth 50marks. Utilising existing ROS stacks willreduce this to 30marks, and doingthis task withnosensororodometricnoisewillreduceyourpossiblemaximal mark byanother 10points. Note that Iexpectyoutoutilisepath planning hereinthefirstinstance -solvingthisproblempurelywithalocal obstacle avoidance algorithmispossible, but willreduce marks byanother 10points. Onthe other hand, combining path planning with alocalobstacle avoidance algorithm(and assuming thatyouimplemented both yourself)willadd20points toyourmark.

Note that marks will be deducted if your robot wanders too far from the optimal (or planned) path, believes it is at a goal when it is far away, etc (these will be judged somewhat subjectively, but you can assume that a 20cm error will cost you one mark, 40cm two marks, etc, for each part of the mark, i.e., moving far away from the optimal line could cost several marks, as could being far away from the goal).

6 Hints

• Both sensor and odometer noise will be present, take a look at the files to see how much noise exists.

• Don’t forget your robot has a physical size.

• There might be a faster way to reach the points than visiting them in order.

• N.B. I may change some of the parameters (e.g., noise, penalties for time/distance) during the assessment. Parameters like noise will be stabilised quickly, but you should make sure you can change them easily in your code.