de9im

de9im is a Javascript library that provides spatial predicate functions defined by the Dimensionally Extended Nine-Intersection Model (DE-9IM) and works with GeoJSON objects. It can test if two geometries have one of the following relationships: contains, coveredby, covers, crosses, disjoint, equals, intersects, overlaps, touches, within. It can be used client-side in a browser or server-side with Node.js.

GETTING STARTED

de9im depends on the Turf.js library for performing spatial operations which must be also included for client-side processing since Turf.js is not bundled with de9im.

In a browser

<script src="https://unpkg.com/@turf/turf" charset="utf-8"></script>
<script src="https://unpkg.com/de9im" charset="utf-8"></script>

In Node

npm install de9im
const de9im = require('de9im');

Then call a predicate function on two geometries

const line = {'type': 'LineString', 'coordinates': [[0, 0], [1, 1], [2, 2]]};
const point = {'type': 'Point', 'coordinates': [1, 1]};
de9im.contains(line, point);
// = true
de9im.disjoint(line, point);
// = false

USAGE

API

The de9im object has the following spatial predicate functions available:

contains
coveredby
covers
crosses
disjoint
equals
intersects
overlaps
touches
within

Each predicate takes two GeoJSON arguments and an optional boolean argument:

de9im.predicate(geojson1, geojson2, [error=true])

It returns true, false, or throws an exception if the geometry types provided are not supported. If the optional argument error is false then unsupported geometries return false instead of throwing an exception. Each predicate should be interpreted as the first argument operating on the second. For example,

de9im.contains(line, point)

should be read as

line contains point?

Data Types

The arguments for every predicate can be any GeoJSON type: Geometry, Feature, GeometryCollection, FeatureCollection. All geometry types are supported: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon. However, only homogenous geometries are supported in collections. For example, a FeatureCollection can have points but can not mix points and lines.

Argument Types

Each predicate has a unique combination of first and second argument geometries that it supports.

• contains, covers

  1st / 2nd	Point	Line	Polygon
  Point	✔️	❌	❌
  Line	✔️	✔️	❌
  Polygon	✔️	✔️	✔️

• coveredby, within

  1st / 2nd	Point	Line	Polygon
  Point	✔️	✔️	✔️
  Line	❌	✔️	✔️
  Polygon	❌	❌	✔️

• crosses

  1st / 2nd	Point	Line	Polygon
  Point	❌	✔️	✔️
  Line	✔️	✔️	✔️
  Polygon	✔️	✔️	❌

• disjoint, intersects

  1st / 2nd	Point	Line	Polygon
  Point	✔️	✔️	✔️
  Line	✔️	✔️	✔️
  Polygon	✔️	✔️	✔️

• equals, overlaps

  1st / 2nd	Point	Line	Polygon
  Point	✔️	❌	❌
  Line	❌	✔️	❌
  Polygon	❌	❌	✔️

• touches

  1st / 2nd	Point	Line	Polygon
  Point	❌	✔️	✔️
  Line	✔️	✔️	✔️
  Polygon	✔️	✔️	✔️

TIPS

The following are some best practices on using de9im:

• Data is expected to be in WGS 84 coordinates as per the GeoJSON standard.

• Data with the GeoJSON bbox attribute already defined will process faster.

• Data with complex geometries (e.g., self-intersections, repeated coordinates) may produce invalid results.

• Data coordinates should be truncated to avoid unrealistically high precision (more than 6 decimal places).

BUILD

To build and test the library locally:

npm install
npm test

LICENSE

Copyright (c) 2019 Daniel Pulido mailto:[e-mail]

Source code is released under the MIT License.