@azohra/meteo.grib

A GRIB2 decoder in pure TypeScript, written because the forecast engine needs grid template 3.1 (rotated latitude-longitude: every ECCC HRDPS, RDPS, REPS, and RAQDPS field) and multi-field messages (NCEP's paired U/V submessages), and no maintained JavaScript decoder provides either. The browser-safe core carries no I/O; JPEG 2000 and the worker pool live in the Node-only @azohra/meteo.grib/j2k-node subpath.

pnpm add @azohra/meteo.grib

Decode a real field

This decodes a committed HRDPS 2 m temperature field (rotated grid, JPEG 2000 packing, the combination that motivated the package) and samples one launch:

// decode-fixture.mjs — run inside grib/ after `pnpm build`
import { readFileSync } from "node:fs";
import {
  decodeFieldValues,
  nearestGridpoint,
  parseFields,
  parseGrid,
  splitMessages,
} from "./dist/index.js";
import { createNodeJ2kDecoder } from "./dist/j2k-node.js";

const bytes = readFileSync("test/fixtures/hrdps-continental-tmp-2m.grib2");
const [field] = parseFields(splitMessages(bytes)[0]);
const grid = parseGrid(field.section3); // rotated lat-lon (GDT 3.1)
const decodeJ2k = await createNodeJ2kDecoder(); // every ECCC field is JPEG 2000
const { values } = decodeFieldValues(field, { decodeJ2k });
const site = nearestGridpoint(grid, 49.3634, -117.2361); // a launch near Nelson, BC
console.log(`${grid.kind} ${grid.ni}x${grid.nj} = ${values.length} points`);
console.log(site);
console.log(`2 m temperature: ${(values[site.index] - 273.15).toFixed(2)} C`);

rotated 2540x1290 = 3276600 points
{
  index: 879425,
  latitude: 49.3642714812993,
  longitude: -117.23441055371016,
  distanceKm: 0.1560769875776412
}
2 m temperature: 23.05 C

Every decode path is accepted bit-for-bit against ecCodes over the frozen twenty-message corpus in test/fixtures/; the gate's full story is at https://meteo.azohra.com/docs/grib/correctness/.

Documentation

The reference lives in docs/ (coverage, the ecCodes gate, and the JPEG 2000 codecs and worker pool each have a page) and is served at https://meteo.azohra.com/docs/grib/.

MIT © Justin Watts