CODEWITHSUNDEEP
node.jsd3.jspolygonr-treepoint-in-polygon
João Pimentel Ferreira
João Pimentel Ferreira

Reputation: 16233

Find in which polygon a GeoJSON point lies in, in NodeJS

Given a defined (lat, lon) geo-point I'm trying to find in which polygon this point lies in. I suppose iterating over all the polygons is not efficient. Is there available any function or library for NodeJS that does this?

const polygon = getPolygonFromPoint(FeatureCollection, x, y);

There are no overlapping polygons, actually I'm using this to detect in which district of a certain country a defined GPS coordinates point lies in.

Upvotes: 3

Views: 2970

Answers (2)

Robin Mackenzie
Robin Mackenzie

Reputation: 19319

For a simple point in polygon test you can check turf which has a booleanPointInPolygon. Turf works in node but you should check for differences between v5 and v6+ around how to use npm accordingly. Points should be long/ lat (not lat/ long) and the polygon can be easily pulled out of the feature geometry of your feature collection.

For a more complex use case where you have many points and many polygons within which to locate them you should consider using rbush.

Note that the rbush library constructs an r-tree out of the bounding boxes of the polygons and not the polygons themselves, so use of an r-tree is just a way to vastly reduce the number of polygons you need to test with booleanPointInPolygon.

Example code for rbush:

const RBush = require("rbush");
const turfBbox = require("@turf/bbox").default;

const geo = {} // your feature collection...
const maxEntriesPerNode = 50; // check the doco
const tree = new RBush(maxEntriesPerNode);
const bbox2Object = (keys, bbox) => ["minX", "minY", "maxX", "maxY"].reduce((o, k, i) => ({...o, [k]: bbox[i]}), {})

// create rtree from feature collection
geo.features.forEach(feature => {
  const leaf = bbox2Object(bboxKeys, turfBbox(feature)); // use bbox of feature
  leaf["id"] = feature.properties.SOME_ID; // add some custom properties
  tree.insert(leaf);
});

// test a random point from your data
const [x, y] = [123, 456]; // should be long, lat
const test = tree.search({minX: x, minY: y, maxX: x, maxY: y});
// test should have an array of leaves per the tree.insert above

You can then perform the booleanPointInPolygon test on this reduced set of polygons.

Upvotes: 4

João Pimentel Ferreira
João Pimentel Ferreira

Reputation: 16233

I implemented that with the library polygon-lookup

const PolygonLookup = require('polygon-lookup')
const featureCollection = {
    type: 'FeatureCollection',
    features: [{
        type: 'Feature',
        properties: { id: 'bar' },
        geometry: {
            type: 'Polygon',
            coordinates: [ [ [ 0, 1 ], [ 2, 1 ], [ 3, 4 ], [ 1, 5 ] ] ]
        }
    }]
}
var lookup = new PolygonLookup(featureCollection)
var poly = lookup.search(1, 2)
console.log(poly.properties.id) // bar

Upvotes: 2

Related Questions