# turf_pip 0.0.2 turf_pip: ^0.0.2 copied to clipboard

A small library for detecting if a point lies inside a polygon

# turf_pip #

A small library for detecting if a point lies inside a polygon.

A port of: point-in-polygon-hao NPM package.

Point in polygon library based on the paper "Optimal Reliable Point-in-Polygon Test and Differential Coding Boolean Operations on Polygons" by Hao.

## Features #

- Works on polygons with holes
- Works with degenerate/self-intersecting polyons
- Returns
`PointInPolygonResult.isOnEdge`

if on the edge,`PointInPolygonResult.isOutside`

if inside and`PointInPolygonResult.isOutside`

if outside - Not effected by floating point errors

### Usage #

Install via `dart pub add turf_pip`

```
import 'package:turf_pip/turf_pip.dart';
const polygon = Polygon(coordinates:[
[
Position.of([1, 1]),
Position.of([1, 2]),
Position.of([2, 2]),
Position.of([2, 1]),
Position.of([1, 1])
]
]);
pointInPolygon(Point(coordinates: Position.of([ 1.5, 1.5 ]), polygon)
// => PointInPolygonResult.isInside
pointInPolygon(Point(coordinates: Position.of([ 4.9, 1.2 ]), polygon)
// => PointInPolygonResult.isOutside
pointInPolygon(Point(coordinates: Position.of([1, 2]), polygon)
// => PointInPolygonResult.isOnEdge
```

**Note:** The input polygon format aligns with the GeoJson specification for polygons. This means that the first and last coordinate in a polygon must be repeated, if not this library will throw an error.

```
var polygonWithHole = Polygon(coordinates:([
[
Position.of([0, 0]),
Position.of([1, 0]),
Position.of([1, 1]),
Position.of([0, 1]),
Position.of([0, 0]),
],
[
Position.of([0.1, 0.1]),
Position.of([0.1, 0.9]),
Position.of([0.9, 0.9]),
Position.of([0.9, 0.1]),
Position.of([0.1, 0.1]),
]
]);
```

The library does not support multi-polygons.

### Comparisons #

Some rough comparisons to similar libraries.
While `point-in-polygon`

is slightly faster in most cases it does not support polygons with holes or degenerate polygons.

```
// For a point in a much larger geometry (700+ vertices)
point-in-poly-hao x 474,180 ops/sec ±0.55% (93 runs sampled)
point-in-polygon x 489,649 ops/sec ±0.75% (91 runs sampled)
robust-point-in-polygon x 376,268 ops/sec ±0.79% (89 runs sampled)
```

```
// For a point in bounding box check
point-in-poly-hao x 29,365,704 ops/sec ±1.30% (90 runs sampled)
point-in-polygon x 42,339,450 ops/sec ±0.78% (95 runs sampled)
robust-point-in-polygon x 20,675,569 ops/sec ±0.65% (95 runs sampled)
```

### Algorithm #

This library is based on the paper Optimal Reliable Point-in-Polygon Test and Differential Coding Boolean Operations on Polygons

### Other notes #

- Works irrespective of winding order of polygon
- Does not appear to be effected by floating point errors compared to
`point-in-polygon`

or`robust-point-in-polygon`