https://github.com/geocrystal/convex_hull

Crystal implementation of finding the convex hull of a finite set of points in the plane
https://github.com/geocrystal/convex_hull

convex-hull convex-hull-algorithms crystal graham-scan hacktoberfest jarvis-march

Last synced: 2 days ago
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Crystal implementation of finding the convex hull of a finite set of points in the plane

• Host: GitHub
• URL: https://github.com/geocrystal/convex_hull
• Owner: geocrystal
• License: mit
• Created: 2019-12-01T18:24:41.000Z (almost 5 years ago)
• Default Branch: master
• Last Pushed: 2024-03-31T10:09:59.000Z (8 months ago)
• Last Synced: 2024-05-06T00:04:51.003Z (6 months ago)
• Topics: convex-hull, convex-hull-algorithms, crystal, graham-scan, hacktoberfest, jarvis-march
• Language: Crystal
• Homepage:
• Size: 39.1 KB
• Stars: 2
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# ConvexHull

![Crystal CI](https://github.com/geocrystal/convex_hull/workflows/Crystal%20CI/badge.svg)

[![GitHub release](https://img.shields.io/github/release/geocrystal/convex_hull.svg)](https://github.com/geocrystal/convex_hull/releases)

[![License](https://img.shields.io/github/license/geocrystal/convex_hull.svg)](https://github.com/geocrystal/convex_hull/blob/master/LICENSE)

Crystal implementation of finding the convex hull of a finite set of points in the plane.

Supported algorithms:

- [Jarvis march](https://en.wikipedia.org/wiki/Gift_wrapping_algorithm)

- [Graham scan](https://en.wikipedia.org/wiki/Graham_scan)

## Installation

1. Add the dependency to your `shard.yml`:

   ```yaml

   dependencies:

     convex_hull:

       github: geocrystal/convex_hull

   ```

2. Run `shards install`

## Computing a Convex Hull

Given X, a set of points in 2-D, the convex hull is the minimum set of points that define a polygon containing all the points of X. If you imagine the points as pegs on a board, you can find the convex hull by surrounding the pegs by a loop of string and then tightening the string until there is no more slack.

The following is an example of a convex hull of 19 points.

![convex hull](/assets/convex.png)

### Instantiate algorithm

This library supports `ConvexHull::GrahamScan` and `ConvexHull::JarvisMarch` inherided from abstract class `ConvexHull::Algorithm`.

It accepts `Array` of one of these:

- `Tuple(Number, Number)`

- `ConvexHull::Point`

- Sub-class of `ConvexHull::Point`

And return `Array` of `ConvexHull::Point`.

```crystal

require "convex_hull"

points = [

  {-10, 3}, {-10, 4}, {-7, 8}, {-7, 2}, {-3, 4},

  {-2, 2}, {7, 3}, {9, 5}, {9, -7}, {5, -10},

  {7, -8}, {5, -4}, {5, -5}, {4, -6}, {2, -7},

  {1, -8}, {-3, -4}, {-4, -6}, {-9, -5},

]

# or

#

# points = [

#   ConvexHull::Point.new(-10, 3),

#   ConvexHull::Point.new(-10, 4),

# ...

# ]

```

### Convex hull

#### Jarvis march

```crystal

graham_scan = ConvexHull::GrahamScan.new(points)

graham_scan.map { |point| {point.x, point.y} }

# => [{-10, 4}, {-10, 3}, {-9, -5}, {5, -10}, {9, -7}, {9, 5}, {-7, 8}]

```

#### Graham scan

```crystal

jarvis_march = ConvexHull::JarvisMarch.new(points)

jarvis_march.map { |point| {point.x, point.y} }

# => [{-10, 4}, {-10, 3}, {-9, -5}, {5, -10}, {9, -7}, {9, 5}, {-7, 8}]

```

The result is an ordered collection of objects of type `ConvexHull::Point`.

## Contributing

1. Fork it ()

2. Create your feature branch (`git checkout -b my-new-feature`)

3. Commit your changes (`git commit -am 'Add some feature'`)

4. Push to the branch (`git push origin my-new-feature`)

5. Create a new Pull Request

## Contributors

- [Anton Maminov](https://github.com/mamantoha) - creator and maintainer