Coordinates, MGRS and grids

Convert and parse positions #

Prerequisites: install the standalone dependency-free MGRS package or import the hosted module. It works in browsers, workers, Node and React Native without MapLibre.

npm install https://maps.example/npm/sw-maps-mgrs-1.0.0.tgz

import { toMgrs, parseMgrs, parsePosition, toDms, toDd,
  mgrsCell, utmFromLngLat, lngLatFromUtm } from '@sw-maps/mgrs';
const at = [120.9842, 14.5995];
console.log(toMgrs(at));          // 51P TS 82848 14992 (1 m)
console.log(toMgrs(at, 1000));    // 51P TS 82 14 (1 km)
console.log(parseMgrs('51PTS8214').center);
console.log(parsePosition('14.5995, 120.9842').lngLat);
console.log(toDms(at), toDd(at));
const utm = utmFromLngLat(at);
console.log(lngLatFromUtm(utm));
const square = mgrsCell(at, 1000); // GeoJSON Polygon with cell properties
console.log(square);

The human coordinate parser accepts common latitude-first input; its returned lngLat always uses longitude first. API query strings and GeoJSON remain longitude first. MGRS digits are truncated, not rounded. parseMgrs returns the square center and cell information; a coarse reference identifies an area, not an exact observed fix.

Display grids #

import { setGrid, gridState, mgrsGridStep } from 'https://maps.example/sw-map.js';
map.once('load', () => {
  setGrid(map, { mgrs: true, graticule: true });
  console.log(gridState(map), mgrsGridStep(map));
});
// Disable both: setGrid(map, { mgrs: false, graticule: false });

Grid generation covers the visible area and is restored after a style change. MGRS shows zone lines, 100 km squares from zoom 5, 10 km from 8, 1 km from 11.5 and 100 m from 14.5. The graticule adapts from degrees to seconds. Grid precision describes displayed cells, not GPS accuracy.

Precision and edge cases #

UTM/MGRS helpers cover latitudes −80° to +84° and account for Norway/Svalbard zone exceptions. They do not provide UPS polar references. Check for null parse results and handle errors instead of guessing a malformed reference. mgrsCell clips a square to its grid-zone boundary; it can be used to build an app’s own sector editor. The viewer’s selected sectors and export workflow are described in Use the reference viewer.