majortom-ts

A TypeScript implementation of the ESA Major TOM equal-area grid system. This is a port of the Python and Go implementations and produces bit-for-bit compatible cell IDs and geometries (validated by a shared cross-language reference dataset).

Installation

npm install @earthgenome/majortom-ts

Usage

import { MajorTomGrid } from "@earthgenome/majortom-ts";
import type { Polygon } from "geojson";

// generate an overlapping grid with cells of 320m square
const grid = new MajorTomGrid(320, true);

// polygon 1/10 of a degree square
const aoi: Polygon = {
  type: "Polygon",
  coordinates: [
    [
      [0, 0],
      [0, 0.1],
      [0.1, 0.1],
      [0.1, 0],
      [0, 0],
    ],
  ],
};

// iterate over the cells that cover the area
for (const cell of grid.generateGridCells(aoi)) {
  console.log(`cell id is ${cell.id()}`);
  console.log(`cell geom is ${JSON.stringify(cell.geom)}`);
}

API

• new MajorTomGrid(d = 320, overlap = true) — create a grid with cell size d (meters) and optional half-cell overlap. Throws if d <= 0.
• grid.generateGridCells(geom) — return the GridCell[] that intersect a GeoJSON Polygon, MultiPolygon, or Feature.
• grid.cellFromId(id) — resolve a GridCell from its (>=11 char) geohash ID.
• grid.migrateCellId(oldId) — map a cell ID from a prior grid version onto the current grid, returning the primary cell containing the decoded centroid.
• GridCell — has geom (GeoJSON Polygon), isPrimary (boolean), and id() (11-char geohash string).

Development

npm install
npm test

License

Distributed under the terms of the MIT license.