index.js

var along = require('turf-along');
var lineDistance = require('turf-line-distance');
var linestring = require('turf-linestring');
var fc = require('turf-featurecollection');

/**
 * Divides a {@link LineString} into chunks of a specified length.
 * 
 * @module turf/line-chunk
 * @category transformation
 * @param {Feature<LineString>} line the line to split
 * @param {Number} segment_length how long to make each segment
 * @param {String} units can be degrees, radians, miles, or kilometers
 * @return {FeatureCollection<LineString>} collection of line segments
 * @example 
 * var line = {
 *   "type": "Feature",
 *   "properties": {},
 *   "geometry": {
 *     "type": "LineString",
 *     "coordinates": [
 *       [
 *         -86.28524780273438,
 *         40.250184183819854
 *       ],
 *       [
 *         -85.98587036132812,
 *         40.17887331434696
 *       ],
 *       [
 *         -85.97213745117188,
 *         40.08857859823707
 *       ],
 *       [
 *         -85.77987670898438,
 *         40.15578608609647
 *       ]
 *     ]
 *   }
 * };
 * 
 * //=line 
 *
 * var result = turf.lineChunk(line, 15, 'miles');
 * 
 * result.features.forEach(function(ft, ind) {
 *   ft.properties.stroke = (ind % 2 === 0) ? '#f40' : '#389979';
 * });
 *
 * //=result
 */
module.exports = function(line, segment_length, units) {
  if (line.type == "LineString") {
    line = {"type": "Feature", "properties": {}, "geometry": line};
  }

  if (lineDistance(line, units) <= segment_length) {
    return fc([line]);
  }

  var coordinates = line.geometry.coordinates.slice();
  var result = [];


  while (coordinates.length > 1) {
    var endpt = along(linestring(coordinates), segment_length, units);
    var tempcoords = [];
    for (var i = 0; i < coordinates.length; i++) {
      tempcoords.push(coordinates[i]);

      if (lineDistance(linestring(tempcoords), units) >= segment_length) {
        tempcoords.pop();
        tempcoords.push(endpt.geometry.coordinates);
        coordinates = coordinates.slice(i);
        coordinates.unshift(endpt.geometry.coordinates);
        result.push(tempcoords);
        break;
      }

      if (i == coordinates.length - 1) {
        coordinates = [];
        result.push(tempcoords);
      }
    }
  }
  
  return fc(result.map(function(coords) {
    return linestring(coords);
  }));
};