https://github.com/mikolalysenko/point-in-region

Fast and exact point in region location
https://github.com/mikolalysenko/point-in-region

Last synced: about 2 months ago
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Fast and exact point in region location

• Host: GitHub
• URL: https://github.com/mikolalysenko/point-in-region
• Owner: mikolalysenko
• License: mit
• Created: 2014-03-28T20:46:15.000Z (over 10 years ago)
• Default Branch: master
• Last Pushed: 2014-04-28T22:34:30.000Z (over 10 years ago)
• Last Synced: 2024-10-20T14:27:52.618Z (2 months ago)
• Language: JavaScript
• Homepage: https://mikolalysenko.github.io/point-in-region
• Size: 1.01 MB
• Stars: 26
• Watchers: 5
• Forks: 2
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
point-in-region

===============

[Locates a point](http://en.wikipedia.org/wiki/Point_location) in a collection of regions.  Point location is exact, takes O(log(n)) time, and the data structure has a space requirement of O(n log(n)).

# Example

```javascript

//First create a list of vertices

var vertices = [

  [0, 0],

  [1, 0],

  [1, 1],

  [0, 1],

  [2, 0],

  [3, 0],

  [3, 1],

  [2, 1],

  [2.25, 0.25],

  [2.75, 0.25],

  [2.75, 0.75],

  [2.25, 0.75]

]

//Regions are defined by lists of loops of vertex indices

var regions = [

  //First region, just a square, one loop

  [ 

    [0, 1, 2, 3]

  ],

  //Second region, square with a hole in the middle

  [

    [4, 5, 6, 7],

    [11, 10, 9, 8]    //Note inner loop has opposite orientation

  ]

]

//Now we create the data structure

var classifyPoint = require("point-in-region")(vertices, regions)

//And we can use it to classify which region contains a given point

var assert = require("assert")

assert.equal(classifyPoint([0.5, 0.5]), 0)

assert.equal(classifyPoint([2.1, 0.1]), 1)

assert.equal(classifyPoint([100000, 10000]), -1)  //Outside points return -1

assert.equal(classifyPoint([2.5, 0.5]), -1)  //Point in center hole is outside region

```

[Here is an in browser demo you can try out yourself:](https://mikolalysenko.github.io/point-in-region)



# Install

```

npm install point-in-region

```

# API

### `var classify = require("point-in-region")(positions, regions)`

Preprocesses a collection of regions to answer point location queries efficiently.

* `positions` is a list of vertex positions for each of the regions

* `regions` is a list of regions encoded as lists of clockwise oriented loops of indices

**Returns** A point membership classification function for the region set

**Note** The regions must obey certain topological and geometric properties for this classification to be correct.  Specifically:

* Any two edges are either disjoint, identical, or meet at exactly one common end point

* The interior of each edge touches at most two regions

### `classify(point)`

Returns the index of the region containing `point`

* `point` is a 2D point encoded as a length 2 array

**Returns** The index of the region containing `point` or `-1` if it is not in any region.

# Credits

(c) 2014 Mikola Lysenko. MIT License