@zwaarcontrast/ol-graticule-luftwaffe-planquadrat

WWII Luftwaffe Planquadrat map reference grids for @zwaarcontrast/ol-graticule.

Renders both Luftwaffe grid systems used during the Second World War:

• Gradnetzmeldeverfahren (GNMV), also called Gradnetz or "grid network", in use from before the war until April 1943 and (in a refined form) for the rest of the war. Six hierarchical levels from the 10° Zusatzzahlgebiet down to the ~1 km Arbeitstrapez (post-1943; pre-1943 ≈ 2.3 km).
• Jägermeldenetz (JMN), the fighter reporting network introduced on 1 May 1943 to support the air defence of the Reich. Replaces the GNMV's 1° Großtrapez with a 5°×10° Jagdtrapez (Nord/Süd halves) and a 20×20 letter-pair Mitteltrapez (AA..UU, no I); shares Kleintrapez, Meldetrapez, and Arbeitstrapez with the post-1943 GNMV.

Cross-service: the Heer used the metric Deutsches Heeresgitter (Gauß-Krüger), often printed alongside GNMV on shared sheets. The Kriegsmarine used the unrelated Marinequadratkarte.

Live demo: https://zwaarcontrast.nl/ol-graticule/ol-graticule-luftwaffe-planquadrat/

Install

npm install @zwaarcontrast/ol-graticule @zwaarcontrast/ol-graticule-luftwaffe-planquadrat ol

Peers: ol ^10, @zwaarcontrast/ol-graticule. No proj4 dependency - all transforms go through OL's built-in 4326 ↔ view-projection conversion.

Usage

import { UniversalGraticule } from '@zwaarcontrast/ol-graticule';
import { LuftwaffeGridSystem } from '@zwaarcontrast/ol-graticule-luftwaffe-planquadrat';

const gridSystem = new LuftwaffeGridSystem({ system: 'gnmv' });
map.addLayer(new UniversalGraticule({ gridSystem }));

The grid draws cell-centered codes (not edge-axis labels) and progressively subdivides as you zoom in.

Options

| Option | Type | Default | What it does | |---|---|---|---| | system | 'gnmv' | 'jmn' | 'gnmv' | Which Luftwaffe grid to render. | | era | 'pre-1943' | 'post-1943' | 'post-1943' | GNMV only. pre-1943 uses the 4-cell Meldetrapez and lo/ro/lu/ru Arbeitstrapez labels. JMN ignores this option (JMN only existed in its post-1943 form). | | maxDepth | 0-5 | 5 | How deep to go: 0 = ZZG only, 5 = full Arbeitstrapez. | | minCellPx | number | 40 | A level becomes the deepest visible only once its cells are at least this big in pixels. | | minLabelPx | number | 40 | Labels for cells smaller than this aren't drawn. | | densificationPoints | number | 50 | Vertices per line for non-affine view projections (e.g. Web Mercator at high latitude). |

Levels and reference format

| Level | Size | GNMV token | JMN token | |---|---|---|---| | Zusatzzahlgebiet (ZZG) | 10° × 10° | 2-3 digits + O/W/SO/SW | same | | Großtrapez | 1° × 1° | 2 digits | (does not exist; replaced by Jagdtrapez + letter MT) | | Jagdtrapez | 5° × 10° | (does not exist) | N or S | | Mitteltrapez | 15' × 30' | 1 digit (1-8, 4×2 layout) | 2 letters AA..UU (no I) | | Kleintrapez | 5' × 10' | 1 digit (1-9) | same | | Meldetrapez | 1'40" × 3'20" (post-1943) 2'30" × 5' (pre-1943) | 1 digit (1-9 or 1-4) | 1 digit (1-9) | | Arbeitstrapez | 33.33" × 1'06.67" (post-1943) 1'15" × 2'30" (pre-1943) | a-i or lo/ro/lu/ru | a-i |

Worked examples

Berlin Reichstag (52.518720° N, 13.376257° E) under post-1943 GNMV:

15   Ost   33   3   9   7    c
ZZG  hemi  GT   MT  KT  MelT AT

ZZG 15 (lon ten-count 1 + lat ten-count 5 for the 10°×10° box at NW corner 59° N, 10° E), Ost (E hemisphere, N hemisphere); Großtrapez 33 (NW corner 53° N, 13° E); Mitteltrapez 3; Kleintrapez 9; Meldetrapez 7; Arbeitstrapez c.

Köln-Butzweilerhof (50°59'28" N, 6°53'42" E) under JMN:

05   Ost   S    NO   3   2     a
ZZG  hemi  JTr  LMT  KT  MelT  AT

ZZG 05, Ost; Jagdtrapez Süd (south half of the 49°-59° N band); Mitteltrapez NO (row N, col O of the 20×20 letter grid inside the 5°×10° Süd half); KT 3, MelT 2, AT a.

Looking up a grid reference for a coordinate

import {
  encodeGnmv,
  encodeJmn,
} from '@zwaarcontrast/ol-graticule-luftwaffe-planquadrat';

encodeGnmv([52.518720, 13.376257]);              // -> "15O33397c"
encodeGnmv([52.518720, 13.376257], 'pre-1943');  // -> "15O33393ru" (depth 5)
encodeGnmv([52.518720, 13.376257], 'post-1943', 1); // -> "15O33"  (cap depth)

encodeJmn([50.991111, 6.895]);                   // -> "05OSNO32a"

Input order is [latitude, longitude]. Returns undefined for points above 89° N.

Reverse: parse a reference back to a coordinate

import {
  parseRef,
  LuftwaffeGridSystem,
} from '@zwaarcontrast/ol-graticule-luftwaffe-planquadrat';
import { ParseError } from '@zwaarcontrast/ol-graticule';

parseRef('15 Ost 33 3 9 7 c');
//   -> { system: 'gnmv',
//        decoded: { canonical: '15O33397c', formatted: '15 Ost 33 3 9 7 c',
//                   bbox: [13.370370..., 52.518519..., 13.388889..., 52.527778...],
//                   center: [52.523148..., 13.379630...],
//                   depth: 5 } }

parseRef('05 Ost S NO 3 2 a');
//   -> { system: 'jmn',
//        decoded: { canonical: '05OSNO32a', ..., depth: 5 } }

// Or, via the GridSystem (returns view-projection coords for the cell centre):
const grid = new LuftwaffeGridSystem({ system: 'jmn' });
try {
  const center = grid.parseCoordinate('05OSNO32a', map.getView().getProjection());
  map.getView().animate({ center });
} catch (err) {
  if (err instanceof ParseError) console.warn(err.reason);
}

parseRef auto-detects the system (JMN is preferred when both grammars accept the input). Lenient input: case-insensitive, whitespace and / separators ignored, umlauts (Süd/Sud/Sued) all accepted, full words (Ost/Süd) and abbreviations (O/SO) both work.

Primary-source validation

The encoding is cross-checked against four wartime primary sources: a NARA Luftwaffe Abschussmeldung (HJ 26 near Katwijk), the Generalstab der Luftwaffe Weltkarte K-34 Sofia (1942), the Deutsche Heereskarte sheet I 35 NW Kreta with its explicit "Zusatzzahl 23 ost" annotation, and a Bundesarchiv RL 12/143 GNMV planning plate. See VALIDATION.md for the worked cross-checks at each level.

Credits and attribution

Reconstructing how a long-disused military reference system actually worked is patient archival research. This package's encoding and decoding rules are entirely derived from the work of others:

• Ron Birch and the Halifax JB837 researchers at prwg.co.uk have the most thorough public write-up of the GNMV and JMN levels, including the pre/post-1943 distinction and the worked Reichstag example used as a reference test in this package.
• The Aircrew Remembered article Luftwaffe Grid Reference System for Action Locations documents the Köln-Butzweilerhof worked example used as the JMN reference test, and credits the (now defunct) http://www.stormbirds.com site for the original write-up.
• Both pages cite earlier work by Andreas Brekken, an archived edition of Flugzeug magazine, and the https://www.gykes.dk site.

If you publish work that uses this package, please cite the prwg.co.uk and aircrewremembered.com pages alongside this implementation.

License

MIT. See LICENSE.