@zwaarcontrast/ol-graticule-rd

@zwaarcontrast/ol-graticule-rd

Dutch Rijksdriehoekstelsel (RD Amersfoort) grids for @zwaarcontrast/ol-graticule:

• RD New (EPSG:28992), the current Dutch national grid.
• RD Old (EPSG:28991), the pre-1989 grid, same projection with x_0 = y_0 = 0.

The RDNAPTRANS 2018 NTv2 datum-shift grid is bundled inline, sub-centimetre accuracy with no asset to fetch and no bundler configuration required.

Live demo: https://zwaarcontrast.nl/ol-graticule/ol-graticule-rd/

Install

npm install \
  @zwaarcontrast/ol-graticule \
  @zwaarcontrast/ol-graticule-projected \
  @zwaarcontrast/ol-graticule-rd \
  ol proj4

Usage

import { UniversalGraticule } from '@zwaarcontrast/ol-graticule';
import { createRDNewGridSystem } from '@zwaarcontrast/ol-graticule-rd';

const gridSystem = createRDNewGridSystem();
map.addLayer(new UniversalGraticule({ gridSystem, style: { edgeLabel: true } }));

Or RD Old:

import { createRDOldGridSystem } from '@zwaarcontrast/ol-graticule-rd';
const gridSystem = createRDOldGridSystem();

Both factories are synchronous and idempotent. They:

• register the CRS with proj4/OL;
• decode and register the bundled RDNAPTRANS 2018 grid on first call (~1 ms);
• pre-configure the valid extent and the Netherlands area-of-use polygon.

Options other than the baked-in ones (CRS, proj4, extent, clip polygon) are forwarded to ProjectedGridSystem, e.g. createRDNewGridSystem({ targetScreenPx: 120 }).

Reverse: parse a typed RD coordinate

The factories return a polygon-clipped ProjectedGridSystem, which inherits parseCoordinate:

import { ParseError } from '@zwaarcontrast/ol-graticule';

try {
  const center = gridSystem.parseCoordinate('155000 463000', map.getView().getProjection());
  map.getView().animate({ center });
} catch (err) {
  if (err instanceof ParseError) console.warn(err.reason);
}

Accepted forms: "155000 463000", "155000, 463000", optional trailing m or km (e.g. "155 463 km"). Validity against the NL clip polygon is not enforced, call isValidCoordinate(coord) on the result if you need to reject Amersfoort-relative locations outside the country.

Exports

Factories (synchronous):

• createRDNewGridSystem(options?) → ProjectedGridSystem
• createRDOldGridSystem(options?) → ProjectedGridSystem

Constants:

• RD_NEW_CRS, RD_NEW_PROJ4, RD_NEW_EXTENT, RD_NEW_CLIP_POLYGON
• RD_OLD_CRS, RD_OLD_PROJ4, RD_OLD_EXTENT, RD_OLD_CLIP_POLYGON
• RDNAPTRANS2018_GRID_NAME

Low-level:

• registerRDNAPTRANS2018(), manually register the bundled grid. Called for you by the factories; use it if you're constructing a ProjectedGridSystem by hand with RD_NEW_PROJ4 / RD_OLD_PROJ4.

Why this package bundles an NTv2 grid

RD (Amersfoort, EPSG:28992) is a Bessel-1841 projection. To move between RD metres and WGS84 / ETRS89 / EPSG:3857, proj4 has to shift between datums. There are two ways to do that:

Method	Residual error (across NL)	Applied where
7-parameter Helmert (the +towgs84=... string, EPSG:4833)	~1 m	proj4's default when no grid is available
RDNAPTRANS 2018 NTv2 grid (rdtrans2018.gsb)	< 1 cm	when +nadgrids=@rdtrans2018 can resolve the grid

A 1 m residual is usually plenty for drawing a graticule on a slippy map, but not for georeferencing maps, overlaying cadastral boundaries, or anything pretending to be survey-grade. RDNAPTRANS 2018 is the grid published by Kadaster and is the canonical WGS84 ↔ RD transformation used by all authoritative Dutch geospatial tooling.

This package therefore:

• Inlines the grid as a base64 string inside the package's compiled JS (~80 KB of source → ~60 KB gzipped on the wire, same order as the raw .gsb). No .gsb asset shipped in dist/, no import.meta.url asset resolution, no bundler-specific plumbing.
• Embeds +nadgrids=@rdtrans2018,@null in the exported proj4 strings, with @null at the end so proj4 falls through to the +towgs84 Helmert transform if the grid is somehow not registered (instead of silently degrading to identity, which would be a ~100 m error).
• Calls registerRDNAPTRANS2018() from inside createRDNewGridSystem() and createRDOldGridSystem() on first use.

Using a non-bundled grid source

If you need a newer RDNAPTRANS grid than the one bundled here, or prefer to load it from a CDN, register it yourself before constructing the grid system and the bundled copy will simply be unused:

import { loadNadgrid } from '@zwaarcontrast/ol-graticule-projected';
import {
  createRDNewGridSystem, RDNAPTRANS2018_GRID_NAME,
} from '@zwaarcontrast/ol-graticule-rd';

await loadNadgrid(RDNAPTRANS2018_GRID_NAME, '/my-assets/rdtrans2018-2024.gsb');
const gridSystem = createRDNewGridSystem();

The RD proj4 strings reference @rdtrans2018 by name; whoever registered the grid under that name first wins, and repeat createRDNewGridSystem() calls won't clobber your custom registration.

License

MIT. The included RDNAPTRANS 2018 grid is published by Kadaster (Dutch Land Registry) and is redistributable; see https://www.nsgi.nl/rdnaptrans for the upstream source and documentation.