README.md

turf-tin

turf tin module

turf.tin(points, propertyName)

Takes a set of points and the name of a z-value property and creates a Triangulated Irregular Network, or a TIN for short, returned as a collection of Polygons. These are often used for developing elevation contour maps or stepped heat visualizations.

This triangulates the points, as well as adds properties called a, b, and c representing the value of the given propertyName at each of the points that represent the corners of the triangle.

Parameters

parameter	type	description
points	FeatureCollection	- a GeoJSON FeatureCollection containing Features with Point geometries
propertyName	string	optional: - name of the property from which to pull z values. This is optional: if not given, then there will be no extra data added to the derived triangles.

Example

// generate some random point data
var points = turf.random('points', 30, {
  bbox: [50, 30, 70, 50]
});
//=points
// add a random property to each point between 0 and 9
for (var i = 0; i < points.features.length; i++) {
  points.features[i].properties.z = ~~(Math.random() * 9);
}
var tin = turf.tin(points, 'z')
for (var i = 0; i < tin.features.length; i++) {
  var properties  = tin.features[i].properties;
  // roughly turn the properties of each
  // triangle into a fill color
  // so we can visualize the result
  properties.fill = '#' + properties.a +
    properties.b + properties.c;
}
//=tin

dx

Find a supertriangle, which is a triangle that surrounds all the vertices. This is used like something of a sentinel value to remove cases in the main algorithm, and is removed before we return any results.

Once found, put it in the "open" list. (The "open" list is for
triangles who may still need to be considered; the "closed" list is
for triangles which do not.)

length

For each open triangle, check to see if the current point is inside it's circumcircle. If it is, remove the triangle and add it's edges to an edge list.

undefined

If this point is to the right of this triangle's circumcircle, then this triangle should never get checked again. Remove it from the open list, add it to the closed list, and skip.

Installation

Requires nodejs.

$ npm install turf-tin

Tests

$ npm test