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3D Path Planning Project 1, Phase 2

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3D Path Planning
Project 1, Phase 2

1 Introduction
In this assignment you will begin building a trajectory generator for a quadrotor by implementing two graph
search algorithms: Dijkstra’s algorithm and A*. The goal of this phase is to compute resolution optimal
paths in a 3D environment from a start position to a goal position that avoids colliding with obstacles. This
project is independent of Phase 1, but we will combine our planning and control algorithms in a subsequent
phase.
2 Code Packet
2.1 Provided Files
• flightsim/world.py
The environments used for this assignment are defined by World objects. As documented in the file
header, the world is defined by a dictionary containing the bounds of the world (’extents’), and a list of
dictionaries of axis-aligned cuboid obstacles (’blocks’), which have ’extents’ and ’colors’. These worlds
can be loaded from .json files like those provided in util/. We recommend you create more examples
for yourself. Please do not submit or modify the World object code or any other files from flightsim/.
• code/occupancy_map.py
In order to find paths with a graph search algorithm in a World, it is necessary to first represent the
environment as a graph. To do this we discretize space into a regular grid and attach graph nodes to
each voxel. An OccupancyMap object is a voxel grid corresponding to a World object. Voxels with
value F alse enclose free space while voxels with value T rue intersect obstacles.
The choice of grid resolution is especially important and impacts both the runtime of the algorithm
as well as its ability to find a path. Another consideration is safety, which becomes critical when
considering real world applications. Since quadrotors are not infinitesimal points but rather physical
objects that take up space, it is important to ensure that generated paths avoid all obstacles in the
environment with some margin. The appropriate choice of margin is a balance between safety and
path length. Choose a margin too small and your quad may strike an obstacle and crash. Choose a
margin too big and the goal may become inaccessible. The provided OccupancyMap class is already
parameterized by the resolution of the discretization and the margin of inflation.
You are free to modify occupancy_map.py, though it is not necessary to complete the assignment.
• code/sandbox.py
This script loads a World, runs your algorithm, and plots the results. It is useful for debugging.
• util/test.py
This script runs tests against all test_*.json maps in util, including any you have created yourself.
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2.2 Tasks
• graph_search.py
Your main task is to implement Dijkstra’s algorithm as described in class. A description of the inputs
and expected outputs can be found in the header of the provided file.
A popular variant of Dijkstra’s algorithm is the A* algorithm. Since both algorithms are very similar,
modify your completed graph search function so that when the astar parameter is T rue, it uses distance
to the goal as a heuristic to guide the search. Remember that any heuristic must be admissible and
consistent; if not, the algorithm is no longer guaranteed to return the shortest path.
3 Grading
For this assignment your grade will be determined by automated testing. Your planner must find optimal
paths through a variety of environments and do so quickly. In addition, you must consider cases where there
is no valid path or when there are no obstacles in the environment. Consider making your own maps and
testing your algorithms on simple cases for which it is easy to reason the correct answer.
4 Submission
When you are finished, submit your code via Gradescope which can be accessed via the course Canvas page.
Your submission should contain:
1. A README file detailing anything we should be aware of.
2. Files graph_search.py, occupancy_map.py, as well as any other Python files you need to run your
code.
Shortly after submitting you should receive an e-mail from no-reply@gradescope.com stating that your
submission has been received. Once the automated tests finish running the results will be available on the
Gradescope submission page. There is no limit on the number of times you can submit your code.
Please do not attempt to determine what the automated tests are or otherwise try to game the automated
test system. Any attempt to do so will be considered cheating, resulting in a 0 on this assignment and possible
disciplinary action.
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