Cosi119a

* **Reading: <a href="/content/topics/homeworks/hw_readings_119/200_hw_119_prr10_2/">Read PRR Chapter 10 Part 2</a>**

*Reminder: Readings are your responsibility. You will be expected to come to class prepared, having read the material, and ready to participate in the discussion*

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## Logistics

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### Factors in Assessment of Projects

* The number of students on the team and ambition of the project
* Expectation is based on the number of people and the available time
* 5-6 weeks @ around 5-10 hrs per week per student
* Quality: Does the project work on repeated runs (not just once)
* Communication: How well explained is the project in the deliverable

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### Standups

* Thank you for submitting
* Reread the instructions!
* Simple set of bullets, not a whole project plan

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### Lab

* Link to [Lab coverage hours](https://docs.google.com/spreadsheets/d/1k_Cpw4YSBKJ2N_m8stS5crLlxtF16Nyu2nb_htBr6as/edit?gid=0#gid=0)
* Link to [Report Robot Problems](https://forms.gle/55RRqHbqZ25pQpBHA)
* Are you able to use the lab
* What additional time slots do you need?
* Remember: `sudo shutdown now` (onboard), power switch off, unplug battery.
* `ROBB` is working again. Remember to report robot problems so we can track them and fix them

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### Review of Fiducials PA
* Fully updated details of the assignment: <a href="/content/topics/robotics/robotics_pas_2/50_fiducials/">PA Fiducials</a>

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## Path Planning

* For now, just focus on a mobile robot like a car
* Goal of path planning: get the robot from where it is to a destination
* Beyond that there are many variations
* What kind of map is present?
* Are the obstacles encountered known ahead of time, and can they move?

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### Types of maps - Graphs

* Define places where Robot can be (nodes)
* Define which ones are connected (edges)
* Edge information includes
  1. What path to take
  1. What the "cost" would be of taking that path (surface, distance, desirability)
* Planning the route becomes a graph searching problem
* Find the "cheapest" path between two nodes

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### Types of maps - Occupancy Grids

* Divide the "area" into a regular grid
* Indicate whether each "cell" in a grid is occupied or free
* Occupancy Grids can be multi-layer
* For example to indicate
  1. access for different types of vehicles
  1. areas that are free but discouraged
* Treat each cell in the grid as a `node` with 4 or 8 edges

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<h3 id="behind-the-scenes">Behind the scenes</h3>

<ul>
  <li>amcl subscribes to a topic <code>geometry_msgs/PoseWith</code></li>
  <li>rviz command <em>2d pose estimate</em> publishes the new proposed pose on that topic</li>
  <li>When amcl receives that message it resets its collection of candidate poses</li>
</ul>

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<h3 id="going-inside-the-nav-stack">Going inside the Nav Stack</h3>

<ul>
  <li>Global planner: works out best path assuming map is accurate
    <ol>
      <li><strong>global costmap</strong>: How safe or unsafe is each spot on the map</li>
      <li>Published on /move_base/global_costmap/costmap</li>
      <li>Planner view shows what the planned path to the nav goal is</li>
    </ol>
  </li>
  <li>Local Planner:
    <ol>
      <li>Adjusts the global plan based on newly detected obstacles</li>
      <li>Map shows square area around robot with further analysis
  1 Color shows safe areas in cold colors (like blue) and dangerous areas in warm colors (like red)</li>
    </ol>
  </li>
</ul>

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<h3 id="navigating-in-code">Navigating in code</h3>

<ul>
  <li>Look at <a href="https://raw.githubusercontent.com/campusrover/rosbook/master/scripts/patrol.py">patrol.py</a></li>
  <li>It is a <code>SimpleActionClient</code> which sends a repeating sequence of two Action Goals to <code>move_base</code></li>
  <li>There’s nothing tricky about itself.</li>
  <li>The challenge might be getting all the other bits set up so that it will work correctly</li>
</ul>

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<h3 id="some-more-references">Some more references:</h3>

<ul>
  <li><a href="http://wiki.ros.org/navigation">Navigation Wiki Page</a></li>
  <li><a href="http://wiki.ros.org/move_base">move_base Wiki Page</a></li>
  <li><a href="https://vimeo.com/106994708">Video about navstack</a></li>
  <li><a href="http://wustl.probablydavid.com/publications/IROS2014.pdf">Paper: Layered Costmaps for Context Sensitive Navigation</a></li>
</ul>

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<h2 class="shadow p-3 bg-white rounded">Thank you. Questions?<img class="img-fluid w-100" src="https://picsum.photos/800/100.jpg" /> <small> (random Image from picsum.photos)</small></h2>