homfen / bentley-ottmann-intersections

A module to check if a polygon self-intersects using the bentley-ottmann algorithm

self-intersects

NOTE For a faster and smaller module I recommend checking out sweepline-intersections

A small module using the Bentley-Ottmann algorithm to detection self-intersections

Install

npm install self-intersects

Documentation

Valid inputs: Geojson Polygon, MultiPolygon

    const findIntersections = require('self-intersects')

    const box = {type: 'Polygon', coordinates: [[[0, 0], [1, 0], [1, 1], [0, 1], [0, 0]]]}
    findIntersections(box)
    // returns array os intersection points

Benchmarks

Tested against

• gpsi - https://www.npmjs.com/package/geojson-polygon-self-intersections
• isects - https://www.npmjs.com/package/2d-polygon-self-intersections

// Switzerland with kinks
// gpsi x 36.78 ops/sec ±2.03% (49 runs sampled)
// bentleyOttmannIntersections x 2,047 ops/sec ±1.79% (89 runs sampled)
// isects x 14.22 ops/sec ±1.73% (40 runs sampled)
// - Fastest is bentleyOttmannIntersections

// Simple Case
// gpsi x 246,005 ops/sec ±1.54% (90 runs sampled)
// bentleyOttmann x 535,293 ops/sec ±1.73% (95 runs sampled)
// - Fastest is bentleyOttmannIntersections

Contributing

• For a live dev server run npm run debug.
  • The geometry being tested can be modified in debug/src/App.vue
• There are a couple of test suites
  • npm run test runs all tests
  • npm run test:e2e does a general test that the correct number of self-intersections are found in the test/fixtures folder
  • npm run test:unit is unit style tests to make sure functions & methods do the right thing
    • these need some love

Further Reading

• Original paper
• Geom algorithms website
• Lecture notes by M Smid from Carleton University