Bentley-Ottman Algorithm for Validating Self-Intersections in Polygons
Last updated 3 years ago by ahlusar1989 .
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Detecting polygon self-intersection in Javascript

An implementation of the O((n + k) log n) Bentley–Ottmann sweep-line algorithm for detecting crossings in a set of line segments (originally forked from Simon Tokumine's iteration of sweepline). The aim was to make something to rapidly detect self-intersecting polygons for client side validation before serialization and storage. However, this implementation can be used for server-side validations (except it being more a statement of intent than actual production ready code).

  • Note: This fork does not contain any client side or browser examples - this entirely server-side validation of floor plan data and geometries.


  • node.js 6.9.1
  • mocha
  • chai

Notable Changes to Implementation

  1. ECMAScript classes that provide a much simpler and clearer syntax to create objects and deal with inheritance.
  2. Point: refactor the isLeftofSegment of Class Point as a static method.
  3. Polygon: fix implicit global variables; rename simple_polygon to isSimplePolygon; refactor the logic according to the rest of the classes.
  4. RedBlackTree: fix the implicit global variables in Kevin Lindsey's implementation.
  5. Sweepline: Rename to Bentley-Ottman; improvements to SweepLine and SweepLine segment logic; refactor the logic according to the new constructor patterns.
  6. EventQueue: add the next method; refactor the logic according to the new constructor pattern.
  7. Updates to the test specification for floor plan data.

Reference Implementation

This is the implementation of the Bentley–Ottmann sweep-line algorithm with an AVL tree:

In use is a variant with a Red-Black tree in lieu of the AVL tree. It has some adjustments and modified methods (for example - no rotateLeft and rotateRight methods).


To run tests, please ensure that you have node.js, mocha, chai and npm installed:

$ npm test

Note that this implementation currently doesn't validate polygons that share the same start and end vertex.


This project is in the worldwide public domain.

This project is in the public domain within the United States, and copyright and related rights in the work worldwide are waived through the CC0 1.0 Universal public domain dedication.

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