Function: fetchProjection()

function fetchProjection(epsg, options?): Promise<string>;

Defined in: epsg.ts:122

Fetches a coordinate system definition from epsg.io.

Uses the native fetch, so it works unchanged in the browser, in Node 18+, and in workers.

Parameters

Parameter	Type	Description
epsg	number	The EPSG code, e.g. 26915. Must be a positive integer.
options	FetchProjectionOptions	Format, timeout, and overrides.

Returns

Promise<string>

The definition as text, trimmed.

Throws

If the code does not exist (epsg.io answers with a 404), the service is unreachable, the request times out or is aborted, or the response is not WKT. Every message names which of those it was.

Examples

Fetch a projection and use it directly

const wkt = await fetchProjection(2027);
await writeShapefileZip(data, { fileName: 'parcels', wkt });

Fetch once, then register it so later calls are offline

import { fetchProjection, registerProjections } from '@crmackey/shapefile-wasm';

registerProjections({ 2027: await fetchProjection(2027) });
await writeShapefileZip(data, { epsg: 2027 });

Ask for a different flavour

const wkt2 = await fetchProjection(4326, { format: 'wkt2' });

Remarks

Only 'esri-wkt' belongs in a .prj. WKT 2 is the better standard, but a .prj containing it will confuse a lot of GIS software — so do not register a WKT 2 string for use as a projection file.

In a browser this is a cross-origin request. epsg.io does send permissive CORS headers, but if your page's Content Security Policy restricts connect-src, add https://epsg.io to it.