Script to convert osm geojson data to osm ways geojson feature pairs

osm-geojson-to-2-node-ways.js

#!/usr/bin/env node

'use strict';

//Streaming parser that filters out osm data leaving just ways.
//Ways are then broken down into node pairs.
//
//ie.
//{
//  "type":"Feature",
//  "id":"way/292294676/3", <-- id gets incremented
//  "properties":{
//    "cycleway":"lane",
//    "highway":"primary",
//    "lanes":"2",
//    "maxspeed":"50",
//    "name":"Harewood Road",
//    "oneway":"yes",
//    "source":"Bing",
//    "id":"way/292294676"
//  },
//  "geometry":{
//    "type":"LineString", <-- linestring broken into just 2 nodes
//    "coordinates":[
//      [172.58113310000002,-43.4852091],
//      [172.57978799999998,-43.48464799999999]
//    ]
//  }
//}


var JSONStream    = require('JSONStream')
  , through       = require('through2')
  , geojsonStream = require('geojson-stream')
  , fs            = require('fs')
  , chalk         = require('chalk')

fs.createReadStream(process.argv[2])

  //parse out each feature block
  .pipe(JSONStream.parse('features.*'))

  //throw out anything but ways
  .pipe(through.obj(function (chunk, enc, cb) {
    if (chunk.id.match(/way\/.*/)) this.push(chunk)
    cb()
  }))

  //split each way linestring into linestrings with just 2 node pairs
  .pipe(through.obj(function (chunk, enc, cb) {
    var feature     = chunk
      , id          = feature.id
      , coordinates = feature.geometry.coordinates
      , i           = 0

    while(coordinates.length > 1) {

      //append to id for uniqueness. eg. way/292294608 becomes way/292294608/0
      feature.id = feature.properties.id = id + '/' + i++

      //shift the first node off the array and set as the new linestring
      //together with the node now at the front of the array
      feature.geometry.coordinates = [coordinates.shift(), coordinates[0]]
      this.push(feature)
    }
    cb()
  }))

  //stream into a geojson feature collection
  .pipe(geojsonStream.stringify())

  //stream into the std out
  .pipe(process.stdout)

  .on('error', function (err) {
    console.error(chalk.red(err.message))
    console.trace()
  })