geojson-tools.js

GeoJSON-Tools is a JavaScript module for working with location data, primarily using the GeoJSON specification.

We created GeoJSON-Tools from rwt.to in order to use it on related projects that rely on GeoJSON (primarily for MongoDB's GeoJSON support).

You are welcome to use it, submit bug reports, add feature and pull requests!

Installation

Install node.js, then:

$ npm install geojson-tools

Documentation

Calculations

• getDistance
• complexify

Conversions

• toGeoJSON
• toArray

Validations

• isGeoJSON

Calculations

### getDistance(array, decimals [optional])

Calculates the distance of an array of locations.

Arguments

• array - an array of locations, in the format [lat, lng].
• decimals - the decimal points to round answer to, defaults to 3 decimal points.

Example

var array = [
    [20, 30],
  [20.5, 29.5]
];
getDistance(array, 4);

// 76.321

To get the distance between two points, pass two points in the array, to get the distance of a linestring, pass the coordinates of the linestring.

### complexify(linestring, distance)

Convert LineString or array of coordinates to a 'complex' line with specified maximum distance between each set of points.

Arguments

• linestring - a valid GeoJSON LineString, or an array of locations, in the format [lat, lng].
• distance - the maximum distance between each two locations, in meters. Minimum distance must be 10 meters.

Example

var array = [
    [20, 30],
  [20.5, 29.5]
];
complexify(array, .5); // 500 meters

/*
[
  [
    20,
    30
  ],
  [
    20.01374457881841,
    29.98625542118159
  ],
  [
    20.02749358953798,
    29.97250641046202
  ],
  [
    20.04124228409795,
    29.95875771590205
  ],
  [
    20.054991756377518,
    29.945008243622482
  ],
  [
    20.068742346786582,
    29.931257653213418
  ],
  [
    20.082493595207826,
    29.917506404792174
  ],
  [
    20.09624419012715,
    29.90375580987285
  ],
  [
    20.109998454446686,
    29.890001545553314
  ],
  [
    20.1237529737179,
    29.8762470262821
  ],
  [
    20.13750307275061,
    29.86249692724939
  ],
  [
    20.151256033129513,
    29.848743966870487
  ],
  [
    20.165010879444292,
    29.834989120555708
  ],
  [
    20.17876504224938,
    29.82123495775062
  ],
  [
    20.192520769690717,
    29.807479230309283
  ],
  [
    20.206277898630216,
    29.793722101369784
  ],
  [
    20.22003390658687,
    29.77996609341313
  ],
  [
    20.233790231590877,
    29.766209768409123
  ],
  [
    20.247544863923423,
    29.752455136076577
  ],
  [
    20.261305062529242,
    29.738694937470758
  ],
  [
    20.275060711787024,
    29.724939288212976
  ],
  [
    20.288822447172574,
    29.711177552827426
  ],
  [
    20.3025819531983,
    29.6974180468017
  ],
  [
    20.3163428239271,
    29.6836571760729
  ],
  [
    20.330106243909288,
    29.669893756090712
  ],
  [
    20.34386828218919,
    29.65613171781081
  ],
  [
    20.357630509669633,
    29.642369490330367
  ],
  [
    20.37139577415928,
    29.62860422584072
  ],
  [
    20.385162033041937,
    29.614837966958063
  ],
  [
    20.398927945160654,
    29.601072054839346
  ],
  [
    20.412692053486403,
    29.587307946513597
  ],
  [
    20.426458446138625,
    29.573541553861375
  ],
  [
    20.4402208587639,
    29.5597791412361
  ],
  [
    20.45398897904669,
    29.54601102095331
  ],
  [
    20.467757803444808,
    29.532242196555192
  ],
  [
    20.481524285475142,
    29.518475714524858
  ],
  [
    20.49529252216346,
    29.50470747783654
  ],
  [
    20.5,
    29.5
  ]
];
*/

distance of 'simple' linestring: 76.321 km
distance of 'complex' linesting: 76.321 km

Note: The algorithms works relatively well, and will return results that are > 99.9% accurate over short distances. Specifying distances > 500 km might return undesireable results. We have also not added the option to specify precision, and precision is set at the default rounding of 3 decimals, this is to avoid infinite loops.

Conversions

### toGeoJSON(array, type)

Takes an input of an array and a GeoJSON type, and returns that GeoJSON object.

Arguments

• array - an array of locations, in the format [lat, lng].
• type - the type of GeoJSON object to return (note that this is not case-sensitive). The default type is 'Point', which is returned when pushing an array of a single set of coordinates. Other types are LineString and Polygon.

Note: Other GeoJSON types will be supported in future versions.

Examples

To convert to GeoJSON::Point

Note that the array can be shallow or nested, but has to contain only one set of coordinates.

var array = [[20, 30]];
toGeoJSON(array); // or toGeoJSON(array, 'point');

// {"type":"Point","coordinates":[30,20]}

To convert to GeoJSON::LineString

var array = [
  [20, 30],
  [20.5, 29.5]
];
toGeoJSON(array, 'linestring');

// {"type":"LineString","coordinates":[[30,20],[29.5,20.5]]}

To convert to GeoJSON::Polygon

The minimum number of coordinates should be 4, and there is no need to add the last coordinate in the array. Polygons with holes are supported, however we currently do not test the validity of the holes.

var array = [
  [20, 30],
  [20.5, 29.5],
  [21, 30.5]
];
toGeoJSON(array, 'polygon');

// {"type":"Polygon","coordinates":[[[30,20],[29.5,20.5],[30.5,21],[30,20]]]}

### toArray(geoobj)

Takes an input of a GeoJSON type, and returns coordinates in [lat, lng] format. A single set of coordinates for a Point, or an array for other types.

Arguments

• geoobj - a valid GeoJSON object of the following types: Point, LineString, Polygon, MultiPoint, MultiLineString or MultiPolygon.

Note: The Feature, FeatureCollection and GeometryCollection objects are unsupported. The logic being that it would make it difficult to work with such deeply nested arrays, and that the primary GeoJSON objects would be mixed.

To convert the above to arrays, rather convert the individual geometries in the feature etc.

Examples

To convert from GeoJSON::Point

Note that the array can be shallow or nested, but has to contain only one set of coordinates.

var geoobj = {"type":"Point","coordinates":[30,20]};
toArray(geoobj);

// [20,30]

To convert from GeoJSON::LineString

var geoobj = {"type":"LineString","coordinates":[[30,20],[29.5,20.5]]};
toArray(geoobj);

// [[20,30],[20.5,29.5]]

To convert from GeoJSON::Polygon

The minimum number of coordinates should be 3, and there is no need to add the last coordinate in the array.

var geoobj = {"type":"Polygon","coordinates":[[[30,20],[29.5,20.5],[30.5,21],[30,20]]]};
toArray(geoobj);

// [[20,30],[20.5,29.5],[21,30.5]]

Validations

### isGeoJSON(obj[, returnError])

Takes an input of an object, and returns a true or false. Include a Boolean to return a validation message for invalid objects.

Arguments

• obj - an object, either valid or invalid GeoJSON.
• returnError - a Boolean indicating whether to return a validation message if obj is invalid. The default returnError is true.

Note: All GeoJSON types are supported in the isGeoJSON check. They are:

• Point
• MultiPoint
• LineString
• MultiLineString
• Polygon
• MultiPolygon
• Feature
• FeatureCollection
• GeometryCollection

Nested GeoJSON objects are validated as part of the supplied object.

Caveats

1. We currently do not check the order of LinearRings inside a Polygon
2. All coordinates supplied are expected to be numbers, we do not parseFloats
3. Though the library expects users to be using WGS84, we do not check bounds of lat and lng

Examples

To validate a valid GeoJSON::Point

var geoobj = {"type":"Point","coordinates":[30,20]};
isGeoJSON(geoobj, true);

// true

To validate an invalid GeoJSON::LineString

var geoobj = {"type":"LineString","coordinate":[[30,20],[29.5,20.5]]};
// note the 'coordinate', expecting 'coordinates'
isGeoJSON(geoobj, true);

// {result: false, message: "invalid GeoJSON type supplied"}