[de9im][de9im-site]

 

de9im is a Javascript library that provides spatial predicate
functions defined by the [Dimensionally Extended Nine-Intersection Model
(DE-9IM)][de9im-wiki] and works with [GeoJSON][geojson-site] 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][node-site].

GETTING STARTED

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

$3

``html


`

$3

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

Then call a predicate function on two geometries

`javascript
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

$3

The de9im object has the following spatial predicate functions available:

`javascript
contains
coveredby
covers
crosses
disjoint
equals
intersects
overlaps
touches
within
`

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

`javascript
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,

`javascript
de9im.contains(line, point)
`
should be read as

`shell
line contains point?
`

$3

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.

$3

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

- contains, covers

| 1st / 2nd | Point | Line | Polygon |
|:------------:|:------------------:|:------------------:|:------------------:|
| Point | :heavy_check_mark: | :x: | :x: |
| Line | :heavy_check_mark: | :heavy_check_mark: | :x: |
| Polygon | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |

- coveredby, within

| 1st / 2nd | Point | Line | Polygon |
|:------------:|:------------------:|:------------------:|:------------------:|
| Point | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
| Line | :x: | :heavy_check_mark: | :heavy_check_mark: |
| Polygon | :x: | :x: | :heavy_check_mark: |

- crosses

| 1st / 2nd | Point | Line | Polygon |
|:------------:|:------------------:|:------------------:|:------------------:|
| Point | :x: | :heavy_check_mark: | :heavy_check_mark: |
| Line | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
| Polygon | :heavy_check_mark: | :heavy_check_mark: | :x: |

- disjoint, intersects

| 1st / 2nd | Point | Line | Polygon |
|:------------:|:------------------:|:------------------:|:------------------:|
| Point | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
| Line | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
| Polygon | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |

- equals, overlaps

| 1st / 2nd | Point | Line | Polygon |
|:------------:|:------------------:|:------------------:|:------------------:|
| Point | :heavy_check_mark: | :x: | :x: |
| Line | :x: | :heavy_check_mark: | :x: |
| Polygon | :x: | :x: | :heavy_check_mark: |

- touches

| 1st / 2nd | Point | Line | Polygon |
|:------------:|:------------------:|:------------------:|:------------------:|
| Point | :x: | :heavy_check_mark: | :heavy_check_mark: |
| Line | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
| Polygon | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |

TIPS

The following are some best practices on using de9im:

- Data is expected to be in [WGS 84][wgs84-wiki] 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:

`shell
npm install
npm test
``

LICENSE

Copyright (c) 2019 Daniel Pulido

Source code is released under the MIT License.

[de9im-site]: https://github.com/dpmcmlxxvi/de9im
[de9im-wiki]: https://en.wikipedia.org/wiki/DE-9IM
[geojson-site]: http://geojson.org/
[node-site]: http://nodejs.org/
[turf-site]: https://turfjs.org
[wgs84-wiki]: https://en.wikipedia.org/wiki/World_Geodetic_System