@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.

Note: GNMV was the geographic grid used primarily by the Luftwaffe. The Heer (army) had its own metric system, the Deutsches Heeresgitter (a Gauß-Krüger kilometre grid), but printed GNMV labels alongside it on cross-service sheets, e.g. Heereskarte I 35 NW Kreta (1942) carries the explicit margin note "Zusatzzahl 23 ost". The Kriegsmarine's Marinequadratkarte is a fundamentally different lettered system, not interoperable with GNMV; for that, see @zwaarcontrast/ol-graticule-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

Four independent wartime documents cross-check different levels of the encoding implemented here.

JMN, all six levels: a Luftwaffe action report at the US National Archives (NARA catalog 131506123) locates an event "5 km nordw. Katwijk, HJ 26". Decoding 05 Ost S HJ 26 under JMN with this package places the cell in the North Sea immediately north-west of Katwijk aan Zee on the Dutch coast, matching the prose description. That single reference exercises the ZZG identity (05 Ost: lat ten-count 5, lon ten-count 0, NW corner 59°N/0°E), the post-1943 Jagdtrapez split (S = 49°-54°N inside 05 Ost), the 20×20 letter-pair Mitteltrapez with I omitted (H = row index 7, J = col index 8), and the Kleintrapez / Meldetrapez subdivision all at once.

GNMV, ZZG + Großtrapez + Mitteltrapez: the Generalstab der Luftwaffe's 1942 Weltkarte 1:1 000 000, sheet K-34 Sofia (the German military edition of the Internationale Weltkarte), prints the GNMV Großtrapez grid across the southern Adriatic, Albania, and the western Balkans. The printed cell digits match this package's rendering across the boundary between ZZG 14 Ost (lon 10°-20°E) and ZZG 24 Ost (lon 20°-30°E), confirming the Großtrapez digit ordering (lon-ones followed by lat-ones within the parent ZZG); inside the GT 91 cell around Valona / Vlorë the sheet also carries the MT 5 overprint, locating it in the 15' × 30' Mitteltrapez with NW corner at 40°30'N / 19°00'E. Available at mapywig.org and on Wikimedia Commons.

GNMV, explicit ZZG label + Großtrapez: the Deutsche Heereskarte sheet I 35 NW Kreta (1:500 000, Fliegerausgabe Europa, OKH / Gen.St.d.H., 1942) carries the explicit marginal annotation "Zusatzzahl 23 ost" and prints GT digits 36 / 46 / 56 / 66 / 76 across Crete's middle latitude band, exactly the cells this package renders for ZZG 23 Ost (NW corner 39°N / 20°E, covering 29°-39°N and 20°-30°E). Available on Wikimedia Commons.

GNMV, ZZG roll-over + Großtrapez + Mitteltrapez: a Luftwaffe planning plate held by the German Federal Archives (Bundesarchiv RL 12/143) prints the full GNMV layout across Northern Germany and the Baltic. The red GT digits run 93 / 94 / 95 along lon 9°-10°E and then flip to 03 / 04 / 05 at lon 10°-11°E, the exact ZZG 05 Ost → 15 Ost boundary this package places at lon=10°E. Each GT cell carries the 4 × 2 Mitteltrapez subdivision (1-8) printed in miniature, and the sheet's Unterteilung legend explains the subdivision scheme used at the deeper levels.

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.