“Must use import to load ES Module” problem

Explanation of the problem

The provided error message indicates an issue with importing an ES module in Node.js v12. Specifically, the error message mentions that the module ‘geodesy/latlon-spherical.js’ cannot be loaded with the ‘require’ function because it is an ES module. The error message suggests using the ‘import’ statement instead of ‘require’ to load the module. In Node.js v12, to use the ‘import’ statement, the ‘–experimental-modules’ flag should be enabled. Therefore, the error message may indicate that the flag is not enabled, or the module is not compatible with Node.js v12.

Additionally, the error message suggests that the module ‘geodesy/latlon-spherical.js’ is an ES module and should be loaded using the ‘import’ statement instead of ‘require’. Therefore, the code block should be updated to use the ‘import’ statement, as follows:

import LatLon from 'geodesy/latlon-spherical.js';

const location = new LatLon(50.068, -5.316);

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Problem solution for “Must use import to load ES Module” problem

node --experimental-modules myscript.mjs

// .babelrc
{
  "presets": [
    [
      "@babel/preset-env",
      {
        "targets": {
          "node": "current"
        }
      }
    ]
  ]
}

// script.js
import { someFunc } from './module.js';
console.log(someFunc());

// module.js
export function someFunc() {
  return 'Hello, world!';
}

Other popular problems with Geodesy

Problem: incompatibility with the ES6 module system

This issue is mainly encountered when using geodesy with Node.js versions 12 and above. The issue arises due to the use of the CommonJS module system, which is not compatible with ES6. Consequently, the user may encounter an error message that reads “Error [ERR_REQUIRE_ESM]: Must use import to load ES Module.”

Solution:

The solution to this problem is to enable ES6 modules when running the Node.js script. To achieve this, the user needs to pass the --experimental-modules flag and the -r esm flag as options when running the Node.js command. This will allow Node.js to support ES6 modules and resolve the incompatibility issue.

$ node --experimental-modules -r esm script.js

Problem: lack of support for some methods in certain scenarios

For example, the LatLonEllipsoidal method of the geodesy library does not support the distanceTo method for points on the antipodal. This issue arises due to the limitations of the Vincenty algorithm, which the method uses. Consequently, the user may encounter an error message that reads “Error: antipodal point.”

Solution:

The solution to this problem is to use an alternative method to compute the distance between points on the antipodal. One such method is the Haversine formula, which can be used as an alternative to the Vincenty algorithm. The user can modify their code to use the Haversine formula when working with antipodal points to avoid the error.

// Using Haversine formula for antipodal points
if (p1.isAntipodalTo(p2)) {
    const lat = Math.abs(p1.lat + p2.lat) / 2;
    const dLat = Math.abs(p1.lat - p2.lat);
    const dLon = Math.abs(p1.lon - p2.lon);
    const a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
        Math.cos(p1.lat) * Math.cos(p2.lat) *
        Math.sin(dLon / 2) * Math.sin(dLon / 2);
    const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    const d = ellipsoid.a * c;
    return new Distance(d, 0, 0);
} else {
    // Using Vincenty algorithm for non-antipodal points
    const result = p1.distanceTo(p2);
    return result;
}

A brief introduction to Geodesy

Most popular use cases for Geodesy

const { LatLonEllipsoidal, Dms } = require('geodesy');

const point1 = new LatLonEllipsoidal(new Dms(52, 12, 13.8, 'N'), new Dms(0, 8, 26.3, 'W'));
const point2 = new LatLonEllipsoidal(new Dms(51, 30, 16.8, 'N'), new Dms(0, 7, 29.6, 'W'));
const distance = point1.distanceTo(point2) / 1000; // in kilometers
console.log(distance);

const { Utm, LatLon } = require('geodesy');

const point = new LatLon(51.5074, -0.1278); // London, UK
const utmCoords = Utm.fromLatLon(point);
console.log(utmCoords);

const { LatLonEllipsoidal, Vector3d } = require('geodesy');

const point1 = new LatLonEllipsoidal(37.771008, -122.41175);
const bearing1 = 116.45;
const point2 = new LatLonEllipsoidal(37.774188, -122.414323);
const bearing2 = 56.5;

const intersection = point1.intersection(point2, new Vector3d(bearing1, bearing2));
console.log(intersection);