turf

turf

a node.js library for performing geospatial operations with geojson

All features are written in a functional manner with no side effects. In nearly all cases, they accept objects created by the point, linestring, polygon, and featurecollection functions, but these are simply for convenience. Any valid geojson Feature of FeatureCollection will do.

npm install turf

---

note: This module is under active development and is in a pre-release form. The first official release is planned mid November 2013. Most features are pretty stable, but expect some changes periodically up until then.

---

Features

• load
• point
• linestring
• polygon
• featurecollection
• extent
• center
• centroid
• explode
• combine
• distance
• buffer
• nearest
• tin
• grid
• planepoint
• inside
• contour

Planned Features

Additional feature requests welcomed and encouraged. To request a feature, please add a github issue with a description.

• bisect
• interpolate
• tag
• area
• filter
• intersect
• quantile
• reclass
• remove
• union
• erase
• smooth

---

Examples:

load

Loads a Feature or FeaturCollection from a file.

t = require('turf')
teojsonFile = '/path/to/file/example.geojson'

t.load(geoJsonFile, function(trees, err){
  if(err) throw err
  console.log(trees)
})

point

Creates a geojson point Feature based on an x and a y coordinate. Properties can be added optionally.

t = require('turf')

var point1 = t.point(-75.343, 39.984)
var point2 = t.point(-75.343, 39.984, {name: 'point 1', population: 5000})
console.log(point1)
console.log(point2)

linestring

Creates a geojson linestring Feature based on a coordinate array. Properties can be added optionally.

t = require('turf')

var linestring1 = t.linestring([[102.0, -10.0], [103.0, 1.0], [104.0, 0.0], [130.0, 4.0]])
var linestring2 = t.linestring([[102.0, -10.0], [103.0, 1.0], [104.0, 0.0], [130.0, 4.0]], 
  {name: 'line 1', distance: 145})
console.log(linestring1)
console.log(linestring2)

polygon

Creates a geojson polygon Feature based on a coordinate array. Properties can be added optionally.

t = require('turf')

var polygon1 = t.point([[[20.0,0.0],[101.0,0.0],[101.0,1.0],[100.0,1.0],[100.0,0.0]]])
var polygon2 = t.point([[[20.0,0.0],[101.0,0.0],[101.0,1.0],[100.0,1.0],[100.0,0.0]]], 
  {name: 'line 1', distance: 145})
console.log(polygon1)
console.log(polygon2)

featurecollection

Creates a geojson FeatureCollection based on an array of features.

t = require('turf')
var pt1 = t.point(-75.343, 39.984, {name: 'Location A'})
var pt2 = t.point(-75.833, 39.284, {name: 'Location B'})
var pt3 = t.point(-75.534, 39.123, {name: 'Location C'})

var fc = t.featurecollection([pt1, pt2, pt3])
console.log(fc)

extent

Calculates the extent of all features and returns a bounding box.

t = require('turf')

t.load('path/to/file/example.geojson', function(err, features){
  if(err) throw err
  t.extent(features, function(extent){
    console.log(extent) // [minX, minY, maxX, maxY]
  })
})

center

Calculates the absolute center point of all features.

t = require('turf')

t.load('path/to/file/example.geojson', function(layer, err){
  if(err) throw err
  t.center(layer, function(center){
    console.log(center)
  })
})

centroid

Calculates the centroid of a polygon Feature or FeatureCollection using the geometric mean of all vertices. This lessons the effect of small islands and artifacts when calculating the centroid of a set of polygons.

t = require('turf')
var poly = t.polygon([[[0,0], [0,10], [10,10] , [10,0]]])

t.centroid(poly, function(err, centroid){
  if(err) throw err
  console.log(centroid) // a point at 5, 5
})

explode

Takes a Feature or FeatureCollection and return all vertices as a collection of points.

t = require('turf')
var poly = t.polygon([[[0,0], [0,10], [10,10] , [10,0]]])

t.explode(poly, function(err, vertices){
  if(err) throw err
  console.log(vertices)
})

combine

Combines an array of point, linestring, or polygon features into multipoint, multilinestring, or multipolygon features.

t = require('turf')
var pt1 = t.point(50, 1)
var pt2 = t.point(100, 101)

t.combine([pt1, pt2], function(err, combined){
  if(err) throw err
  console.log(combined)
})

inside

Checks to see if a point is inside of a polygon. The polygon can be convex or concave.

t = require('turf')
var poly = t.polygon([[[0,0], [50, 50], [0,100], [100,100], [100,0]]])
var pt = t.point(75, 75)

t.inside(pt, poly, function(err, isInside){
  if(err) throw err
  console.log(isInside) // true
})

buffer

Buffers a point feature to a given radius. Lines and Polygons support coming soon. Unit selection coming soon too (degrees, miles, km).

t = require('turf')
var pt = t.point(0, 0.5)

t.buffer(pt, 10, function(err, buffered){
  if(err) throw err
  console.log(buffered)
})

distance

Calculates the distance between two point features in miles or kilometers. This uses the haversine formula to account for global curvature.

t = require('turf')
var point1 = t.point(-75.343, 39.984)
var point2 = t.point(-75.534, 39.123)
var unit = 'miles' // or 'kilometers'

t.distance(point1, point2, unit, function(err, distance){
  if(err) throw err
  console.log(distance)
})

nearest

Returns the nearest point feature.

t = require('turf')    
var inPoint = t.point(-75.4, 39.4, {name: 'Location A'})

var pt1 = t.point(-75.343, 39.984, {name: 'Location B'})
var pt2 = t.point(-75.833, 39.284, {name: 'Location C'})
var pt3 = t.point(-75.534, 39.123, {name: 'Location D'})
var inFeatures = t.featurecollection([pt1, pt2, pt3])

t.nearest(inPoint, inFeatures, function(err, closestPoint){
  if(err) throw err
  console.log(closestPoint)
})

tin

Takes a set of points and the name of a z-value property and creates a tin (Triangulated Irregular Network). These are often used for developing elevation contour maps or stepped heat visualizations.

t = require('turf')
var z = 'elevation'

t.load('/path/to/pointsfeatures/elevationPoints.geojson', function(err, points){
  t.tin(points, z, function(err, tin){
    if(err) throw err
    console.log(tin)
  })
})

grid

Takes a bounding box and a cell depth and outputs a feature collection of points in a grid.

t = require('turf')
var depth = 15

t.grid([0,0,10,10], depth, function(err, grid){
  console.log(grid) // 15x15 grid of points in a FeatureCollection
})

planepoint

Takes a trianglular plane and calculates the z value for a point on the plane.

t = require('turf')
var point = t.point(-75.3221, 39.529)
// triangle is a polygon with "a", "b", and "c" values representing
// the values of the coordinates in order.
var triangle = t.polygon(
  [[[-75.1221,39.57],[-75.58,39.18],[-75.97,39.86]]], 
  "properties": {"a": 11, "b": 122, "c": 44}
  )

t.planepoint(point, triangle, function(err, zValue){
  if(err) throw err
  console.log(zValue)
})

contour

Takes a FeatureCollection of points with z values and an array of value breaks and generates contour polygons. This is a great way to visualize interpolated density on a map. It is often used for elevation maps, weather maps, and isocrones. The main advantage over a heat map is that contours allow you to see definitive value boundaries, and the polygons can be used to aggregate data. For example, you could get the 5000 ft elevation contour of a mountain and the 10000 ft elevation contour, then aggregate the number of trees in each to see how elevation affects tree survival.

note: this function currently has a bug. It will only work on square data. A fix is in progress and should be out within the week. 10/29/13

t = require('turf')
var z = 'elevation'
var resolution = 15
var breaks = [.1, 22, 45, 55, 65, 85,  95, 105, 120, 180]

t.load('../path/to/points.geojson', function(err, points){
  t.contour(points, z, resolution, breaks, function(err, contours){
    if(err) throw err
    console.log(contours)
  })
})

---

Development

Run Tests

cd test 
mocha .

---

Credits

This library is built and maintained by @morganherlocker. If you would like to contribute, please do! :)

I have taken a "picasso" approach to building this library, borrowing from existing code when available and modifying it to meet coding styles and standards of turf. Here is a list of places I have pulled ideas and/or code from (all open source or public domain, as far as I know):

https://github.com/ironwallaby/delaunay

https://github.com/jasondavies/conrec.js

http://stackoverflow.com/a/839931/461015

http://en.wikipedia.org/wiki/Haversine_formula

http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm

https://github.com/mbloch/mapshaper

http://en.wikipedia.org/wiki/Delaunay_triangulation

http://svn.osgeo.org/grass/grass/branches/releasebranch_6_4/vector/v.overlay/main.c

http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html

http://en.wikipedia.org/wiki/Even%E2%80%93odd_rule

https://github.com/substack/point-in-polygon/blob/master/index.js