osm-ways-to-geojson

demo.js

const axios = require("axios");
const querystring = require("querystring");
const _ = require("lodash");
const fs = require("fs");
const path = require("path");

const osmWays = [
  {
    // 三六九到黑森林入口
    id: 464086142,
    start: 1518876742,
    end: 1518875824
  },
  {
    // 黑森林
    id: 464085687
  },
  {
    // 黑森林出口到圈谷底部岔路
    id: 464085679
  }
];

async function transform() {
  try {
    let coordinates = [];
    for (let i = 0; i < osmWays.length; i += 1) {
      const way = osmWays[i];

      // get nodes of way from OSM by overpass api
      const query = `
        [out:json];
          way(${way.id});
          (._;>;);
        out;
      `;
      const { data: { elements } } = await axios.post(
        "http://overpass-api.de/api/interpreter",
        querystring.stringify({ data: query })
      );
      const nodeIds = _.last(elements).nodes;

      // find the start and end node index of way by node id
      const startIndex = way.start
        ? nodeIds.findIndex(nodeId => nodeId === way.start)
        : 0;
      const endIndex = way.end
        ? nodeIds.findIndex(nodeId => nodeId === way.end)
        : nodeIds.length - 1;

      // concatenate nodes into the coordinates of geoJSON
      coordinates = coordinates.concat(
        nodeIds.slice(startIndex, endIndex + 1).map(nodeId => {
          const node = elements.find(e => e.id === nodeId);
          return [node.lon, node.lat];
        })
      );
    }

    // create and save the geoJSON
    const geoJSON = {
      type: "LineString",
      coordinates: coordinates
    };
    fs.writeFileSync(
      path.resolve(__dirname, "demo.json"),
      JSON.stringify(geoJSON)
    );
    console.log("done");
  } catch (error) {
    console.log(error);
  }
}

transform();

demo.json

{"type":"LineString","coordinates":[[121.2547261,24.392336],[121.2546085,24.392463],[121.2545623,24.3925245],[121.2544607,24.3926065],[121.2544167,24.392652],[121.2543148,24.3927777],[121.2542084,24.3929043],[121.2539094,24.3932588],[121.2536411,24.3934628],[121.2533581,24.3936374],[121.253381,24.3934787],[121.2534775,24.3932148],[121.2534573,24.3930733],[121.2533833,24.3931192],[121.2532527,24.3932312],[121.2531908,24.3932995],[121.253116,24.3933501],[121.2529954,24.3933757],[121.2529963,24.3931125],[121.2529837,24.3930357],[121.2529526,24.3929556],[121.2525988,24.3932808],[121.2526037,24.3931855],[121.2526142,24.3931005],[121.2525924,24.3930331],[121.2525382,24.3928469],[121.2522931,24.39312],[121.2522336,24.3932119],[121.2521934,24.3932534],[121.2521338,24.3932979],[121.2519025,24.3933662],[121.2517405,24.3934356],[121.2515785,24.3935373],[121.2513913,24.393712],[121.2514119,24.3935082],[121.2514175,24.3933528],[121.251115,24.393628],[121.251115,24.393628],[121.2508919,24.3935861],[121.2507524,24.3936643],[121.2503555,24.3935959],[121.2501087,24.3935764],[121.2497824,24.3936839],[121.2493148,24.3937132],[121.2490036,24.3937718],[121.2487676,24.3938206],[121.2486496,24.3937522],[121.2483814,24.393762],[121.248156,24.3939477],[121.2476303,24.3940161],[121.2472763,24.3940649],[121.2471583,24.3942408],[121.2468793,24.3942506],[121.2465682,24.3942408],[121.2464931,24.3943678],[121.2461068,24.3942897],[121.2458386,24.3942994],[121.2457742,24.3944851],[121.2453558,24.3945535],[121.2448945,24.3945242],[121.2447228,24.3944362],[121.2444439,24.3942506],[121.2442186,24.3941431],[121.2440469,24.3939868],[121.243768,24.3939574],[121.2436821,24.39385],[121.2435856,24.3937132],[121.2432852,24.3935764],[121.2431457,24.3934591],[121.2428667,24.3933126],[121.2426736,24.3931562],[121.2426522,24.393039],[121.2425019,24.3929803],[121.2423303,24.393039],[121.2422659,24.3929022],[121.2421157,24.3927361],[121.2419655,24.3926677],[121.2417509,24.3927654],[121.2417402,24.3926481],[121.2416329,24.3925015],[121.2415042,24.392355],[121.2413432,24.3920423],[121.2411823,24.3919934],[121.2410536,24.3917785],[121.2408712,24.3916124],[121.2407961,24.3914658],[121.2405815,24.3914658],[121.2405708,24.3912997],[121.2402704,24.3911922],[121.2402489,24.3910652],[121.2401201,24.3909382],[121.2399378,24.3907134],[121.2399056,24.3905375],[121.2397446,24.3904496],[121.2397339,24.3901955],[121.2394871,24.3903128],[121.2393048,24.3902932],[121.239455,24.390088],[121.2392404,24.3900783],[121.2392404,24.3898731],[121.239412,24.389619],[121.2393369,24.3895506],[121.2390365,24.3895311],[121.2388756,24.3894529],[121.2385967,24.3895115],[121.2384035,24.3893845],[121.2381782,24.3893357],[121.2379744,24.3893747],[121.2378885,24.3891793],[121.2377062,24.3891207],[121.2374701,24.3890425],[121.2372019,24.3889741],[121.2372019,24.3889741],[121.2370732,24.3889057],[121.2367406,24.3886907],[121.2364723,24.3885637],[121.2364433,24.3884581],[121.2364187,24.3883683],[121.2363329,24.3881631],[121.2363216,24.3880767]]}