TWD97 convert to WGS84 with MongoDB

dbUpdate_twd97_to_wgs84.js

// * set database.
db = db.getSiblingDB('local');

// * coordinate converter.
// https://kuro.tw/posts/2015/06/11/js-note-twd97-convert-to-longitude-and-latitude/
function twd97_to_wgs84(x, y) {
  let pow = Math.pow, M_PI = Math.PI;
  let sin = Math.sin, cos = Math.cos, tan = Math.tan;
  let a = 6378137.0, b = 6356752.314245;
  let lng0 = 121 * M_PI / 180, k0 = 0.9999, dx = 250000, dy = 0;
  let e = pow((1 - pow(b, 2) / pow(a, 2)), 0.5);

  x -= dx;
  y -= dy;

  let M = y / k0;

  let mu = M / (a * (1.0 - pow(e, 2) / 4.0 - 3 * pow(e, 4) / 64.0 - 5 * pow(e, 6) / 256.0));
  let e1 = (1.0 - pow((1.0 - pow(e, 2)), 0.5)) / (1.0 + pow((1.0 - pow(e, 2)), 0.5));

  let J1 = (3 * e1 / 2 - 27 * pow(e1, 3) / 32.0);
  let J2 = (21 * pow(e1, 2) / 16 - 55 * pow(e1, 4) / 32.0);
  let J3 = (151 * pow(e1, 3) / 96.0);
  let J4 = (1097 * pow(e1, 4) / 512.0);

  let fp = mu + J1 * sin(2 * mu) + J2 * sin(4 * mu) + J3 * sin(6 * mu) + J4 * sin(8 * mu);

  let e2 = pow((e * a / b), 2);
  let C1 = pow(e2 * cos(fp), 2);
  let T1 = pow(tan(fp), 2);
  let R1 = a * (1 - pow(e, 2)) / pow((1 - pow(e, 2) * pow(sin(fp), 2)), (3.0 / 2.0));
  let N1 = a / pow((1 - pow(e, 2) * pow(sin(fp), 2)), 0.5);

  let D = x / (N1 * k0);

  let Q1 = N1 * tan(fp) / R1;
  let Q2 = (pow(D, 2) / 2.0);
  let Q3 = (5 + 3 * T1 + 10 * C1 - 4 * pow(C1, 2) - 9 * e2) * pow(D, 4) / 24.0;
  let Q4 = (61 + 90 * T1 + 298 * C1 + 45 * pow(T1, 2) - 3 * pow(C1, 2) - 252 * e2) * pow(D, 6) / 720.0;
  let lat = fp - Q1 * (Q2 - Q3 + Q4);

  let Q5 = D;
  let Q6 = (1 + 2 * T1 + C1) * pow(D, 3) / 6;
  let Q7 = (5 - 2 * C1 + 28 * T1 - 3 * pow(C1, 2) + 8 * e2 + 24 * pow(T1, 2)) * pow(D, 5) / 120.0;
  let lng = lng0 + (Q5 - Q6 + Q7) / cos(fp);

  lat = (lat * 180) / M_PI;
  lng = (lng * 180) / M_PI;
  return [lat, lng]
}

// * test tools for developing.
function convertPrint(doc) {
  let map = doc.geometry.coordinates
  let name = doc.properties.MARKNAME1
  printjson(`${name} :  ${map}`)

  let convertMap = twd97_to_wgs84(map[0], map[1])
  printjson(`${name} :  ${convertMap}`)
}

// * Main function
// update a document.  TWD97 --> WGS84.
function updateFromTwd97ToWGS84(doc) {
  let map = doc.geometry.coordinates
  let coordinates = twd97_to_wgs84(map[0], map[1])  // convert coordinate format from TWD97 to WGS84
  let lonLat = [coordinates[1], coordinates[0]]     // coordinates: [ Lon, Lat ]

  db.tw_railway_station.update(
    { "_id": doc._id }, // value 要是 ObjectId("XxxxXXxxxxx")，不能只是傳入 id string.
    {
      $set: {
        "geometry.coordinates": lonLat
        // $set 只更新特定 filed 不影響其他的 ; dot notation 很好用
      }
    }
  );
  print(doc.properties.MARKNAME1 + ` is converted and updated.`)
}

// * excute code to operate MongoDB database.
// db.tw_railway_station.find().forEach(doc => printjson(doc) );
// db.tw_railway_station.find().forEach(doc => convertPrint(doc) );
db.tw_railway_station.find().forEach(document => updateFromTwd97ToWGS84(document));