Does this support multiple polygons?

I noticed that the input array was a relatively strange format (doubly nested array) and was curious if this meant that arrays of multiple polygons were supported? Is this implicitly supported because of the hole support?

// Input shape(s)
const polygon = [
  [
    [0,0], [1,0], [1, 1], [0,1], [0,0]
  ],
  [
    [2,2], [3,2], [3,3], [2,3], [2,2]
  ]
]

// Tests
const tests = [
  [0.5, 0.5],
  [0,0],
  [0.5, 0],
  [2, 0],

  [2,2],
  [2.5, 2.5],
  [2.5, 2],
  [2, 1]
];

// Verification
tests.forEach((test) => {
  let isInside = inside(test, polygon);
  isInside = isInside === true || isInside === 0;

  console.log(isInside, test);
})

It also appears to work as expected if the two “shape” subarrays are combined (assuming both are closed properly)?

[rowanwins]

Hi @kendallroth

That’s a good question, I hadn’t actually thought about it!

The choice of doubly-nested arrays was to align to how geojson structures things (I mainly deal with mapping problems). Using your structure above is how we’d normally handle holes in geojson.

Below are some examples of geojson coordinate stucture

const geojsonPolygonWithHole = [
  [
    [0,0], [1,0], [1, 1], [0,1], [0,0]
  ],
  [
    [0.1,0.1], [0.1,0.9], [0.9,0.9], [0.9,0.1], [0.1,0.1]
  ]
]

// Note for multipoly we wrap the coordinates another level deeper
const geojsonMultiPolygon = [
  [
    [
      [0,0], [1,0], [1, 1], [0,1], [0,0]
    ]
  ],
  [
    [
      [2,2], [3,2], [3,3], [2,3], [2,2]
    ]
  ]
]

Note that using the geojson multipolygon approach currently this wouldn’t work with the library.

So I probably ought to be more explicit in describing the expected input format! Although it’s interesting that it works with your approach, although obviously your approach also means your multipolys can’t have holes.

Open to suggestions/thoughts at least around documenting expected behaviour 😃

[rowanwins]

I’ve update the readme to indicate that the input is in the geojson format.