Simplify a Polygon and MultiPolygon FeatureCollection

simplify.js

#!/usr/bin/env node
/*
 * cat my-features.json | ./simplify.js 0.0001 > my-simplified-features.json
 */
'use strict';

var simplify = require('turf-simplify');
var concat = require('concat-stream');

var TOLERANCE = 0.01;
if (process.argv.length === 3) {
  TOLERANCE = parseFloat(process.argv[2]);
}

process.stdin.pipe(concat(function (input) {
  var data = JSON.parse(input);
  data.features = data.features.map(function (feature) {
    if (feature.geometry.type === 'MultiPolygon') {
      return {
        type: 'Feature',
        properties: feature.properties,
        geometry: {
          type: 'MultiPolygon',
          coordinates: feature.geometry.coordinates.map(function (polyCoords) {
            return simplify({
              type: 'Feature',
              geometry: {
                type: 'Polygon',
                coordinates: polyCoords
              }
            }, TOLERANCE, true).geometry.coordinates;
          })
        }
      };
    }
    return simplify(feature, TOLERANCE, true);
  });
  process.stdout.write(JSON.stringify(data));
  process.stdout.write('\n');
}));