geo-point-in-polygon

determine if a lon,lat point is inside a polygon using great circle calculations

example

The benefits of great circle calculations are very apparent at high latitudes.

The triangle described here covers the pole even though the latitudes of each point in the triangle is further south.

var geoPointInPolygon = require('geo-point-in-polygon')
console.log(geoPointInPolygon(
  [0,90], // north pole
  [
    [-156.78872,+71.29058], // utqiagvik
    [- 51.72157,+64.18347], // nuuk
    [+ 88.20270,+69.35350], // norilsk
  ]
)) // true

also gracefully handles the anti-meridian without special cases:

var geoPointInPolygon = require('geo-point-in-polygon')
console.log(geoPointInPolygon(
  [+178.44149,-18.14161], // suva
  [
    [+139.69171,+35.68950], // tokyo
    [+174.76667,-36.86667], // auckland
    [-155.09000,+19.72972], // hilo
  ]
)) // true

api

var geoPointInPolygon = require('geo-point-in-polygon')
var geoPointInPolygonNested = require('geo-point-in-polygon/nested')
var geoPointInPolygonFlat = require('geo-point-in-polygon/flat')

geoPointInPolygon(point, polygon, start=0, end=polygon.length, outside=ANTIPODE)

Return whether point is inside polygon.

• polygon is an array of [lon,lat] points or a flat array of [lon0,lat0,lon1,lat1,...]
• point is a 2-item array [lon,lat] of decimal degrees
• start is an inclusive offset into polygon. default 0
• end is an exclusive offset into polygon. default polygon.length
• outside is a [lon,lat] coordinate that is known to be outside the polygon

By default, outside is set to the antipode of the first point in polygon which should work for all polygons that span less than 180 degrees of longitude. If your polygon spans >=180 degrees, you will need to use other domain information to find a point known to be outside the polygon.

install

npm install geo-point-in-polygon

license

bsd