Gutza / bentley-ottman

Bentley-Ottman sweepline algorithm implementation in js

Bentley-Ottman sweepline

This is a Bentley-Ottman sweepline algorithm implementation, both for Node.js and browser. It finds all intersection in a set of 2D segments, uses balanced avl tree internally.

Demo

var findIntersections = require('bentley-ottman-sweepline');

var segments = [
    [[0, 1], [3, 1]],
    [[2, 0], [2, 2]]
]

console.log(findIntersections(segments));

Segment traceability

There are several implementations of this algorithm available in JavaScript, see the NPM repository. This is neither the fastest, nor the most reliable (it's known to fail for multiple cartesian intersections; this is obviously fixable with a little TLC). Having said all that, this particular implementation is the only one which offers segment traceability. That is, you can define your segments as

let segments = [
	[[0,0], [1,1]],
	[[1,0], [0,1]]
];

console.log(JSON.stringify(findIntersections(segments)));

// [{"x":0.5,"y":0.5,"segmentID":["0","1"]}]

but you can also define your segments as

let segments = {
	MySpecialSegmentA: [[0,0], [1,1]],
	MySpecialSegmentB: [[1,0], [0,1]],
};

console.log(JSON.stringify(findIntersections(segments)));

// [{"x":0.5,"y":0.5,"segmentID":["MySpecialSegmentA","MySpecialSegmentB"]}]

This is the only Bentley-Ottman implementation that offers this feature.

Browser build

In order to use the library in the browser, simply open a console in the root folder and execute

npx browserify src/findIntersections.js -t babelify -o findIntersectionsBundle.js -s findIntersections

You can now use findIntersectionsBundle.js in the browser, and you have access to findIntersections(). Change -o findIntersectionsBundle.js to a different filename if you want to change the name of the output file, and change -s findIntersections to some other name if you want to alias function findIntersections() for some reason.