Polygon intersection bug

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# IntelliJ project files
.idea
*.iml
out
gen
node_modules

actual.json

clip.json

expected.json

index.js

// npm install martinez-polygon-clipping polygon-clipping
// node index.js

const fs = require('fs');

const martinez = require('martinez-polygon-clipping');
const polygonClipping = require('polygon-clipping');

const input = require('./input.json');
const clip = require('./clip.json');

function apply(op, area, clip) {
  // console.log(input);
  // console.log(clip);
  const result = op(
    area,
    clip,
  );
  return JSON.stringify({
    'type': 'FeatureCollection',
    'features': [{
      'type': 'Feature',
      'properties': {},
      'geometry': {
        'type': 'MultiPolygon',
        'coordinates': result
      }
    }]
  });
}

fs.writeFileSync('./expected.json', apply(
  polygonClipping.difference,
  input.features[0].geometry.coordinates,
  clip.features[0].geometry.coordinates
));
fs.writeFileSync('./actual.json', apply(
  martinez.diff,
  input.features[0].geometry.coordinates,
  clip.features[0].geometry.coordinates
));

input.json

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [6,2.5],
            [12,2.5],
            [12,13],
            [6,13],
            [6,2.5]
          ],
          [
            [8,3.5],
            [10,3.5],
            [10,6],
            [8,6],
            [8,3.5]
          ],
          [
            [8, 12],
            [10, 12],
            [10, 9],
            [8, 9],
            [8, 12]
          ]
        ]
      }
    }
  ]
}

package-lock.json

{
  "name": "7d75093e5e8d9fe52008871c109bb855",
  "version": "1.0.0",
  "lockfileVersion": 1,
  "requires": true,
  "dependencies": {
    "babel-plugin-add-module-exports": {
      "version": "0.2.1",
      "resolved": "https://registry.npmjs.org/babel-plugin-add-module-exports/-/babel-plugin-add-module-exports-0.2.1.tgz",
      "integrity": "sha1-mumh9KjcZ/DN7E9K7aHkOl/2XiU="
    },
    "martinez-polygon-clipping": {
      "version": "0.5.0",
      "resolved": "https://registry.npmjs.org/martinez-polygon-clipping/-/martinez-polygon-clipping-0.5.0.tgz",
      "integrity": "sha512-FvHURxJTieS4LEHL+aJmWbqCUBk2GrYU5zolgXNAQLJsjnAff7Hqqk5MM1Kl91FnPOcyiAs/cVey11bb0D7qug==",
      "requires": {
        "splaytree": "^0.1.4",
        "tinyqueue": "^1.2.0"
      }
    },
    "polygon-clipping": {
      "version": "0.9.2",
      "resolved": "https://registry.npmjs.org/polygon-clipping/-/polygon-clipping-0.9.2.tgz",
      "integrity": "sha512-UO+53kvxmuyMpO6RqepUTj3lQPcFJ6NbqJbfwxcOZv3xTuWUQd2q12JiyT5Sd2NAHgxzHH2ht2BQSuclJaEyDQ==",
      "requires": {
        "babel-plugin-add-module-exports": "^0.2.1",
        "splaytree": "^2.0.2",
        "tinyqueue": "^1.2.3"
      },
      "dependencies": {
        "splaytree": {
          "version": "2.0.3",
          "resolved": "https://registry.npmjs.org/splaytree/-/splaytree-2.0.3.tgz",
          "integrity": "sha512-IziTvWQv9F1EiKq9XveosQRGTLrdUW0jLokpmAXz0+hnLgBZitvU0j4gUvCGASKwUQvCZaofhff1H8OmE2LRdA=="
        }
      }
    },
    "splaytree": {
      "version": "0.1.4",
      "resolved": "https://registry.npmjs.org/splaytree/-/splaytree-0.1.4.tgz",
      "integrity": "sha512-D50hKrjZgBzqD3FT2Ek53f2dcDLAQT8SSGrzj3vidNH5ISRgceeGVJ2dQIthKOuayqFXfFjXheHNo4bbt9LhRQ=="
    },
    "tinyqueue": {
      "version": "1.2.3",
      "resolved": "https://registry.npmjs.org/tinyqueue/-/tinyqueue-1.2.3.tgz",
      "integrity": "sha512-Qz9RgWuO9l8lT+Y9xvbzhPT2efIUIFd69N7eF7tJ9lnQl0iLj1M7peK7IoUGZL9DJHw9XftqLreccfxcQgYLxA=="
    }
  }
}

package.json

{
  "name": "7d75093e5e8d9fe52008871c109bb855",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "run": "node index.js"
  },
  "repository": {
    "type": "git",
    "url": "git+ssh://git@gist.github.com/7d75093e5e8d9fe52008871c109bb855.git"
  },
  "author": "",
  "license": "ISC",
  "bugs": {
    "url": "https://gist.github.com/7d75093e5e8d9fe52008871c109bb855"
  },
  "homepage": "https://gist.github.com/7d75093e5e8d9fe52008871c109bb855",
  "dependencies": {
    "martinez-polygon-clipping": "^0.5.0",
    "polygon-clipping": "^0.9.2"
  }
}