@zwaarcontrast/ol-graticule-heeresgitter

WWII Wehrmacht map reference grids for @zwaarcontrast/ol-graticule: the Deutsches Heeresgitter (DHG) metric kilometre grid plus the Heeresmeldenetz (HMN) orange letter-cell overprint, in both planar and geographic variants.

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

Install

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

Peers: ol ^10, @zwaarcontrast/ol-graticule, @zwaarcontrast/ol-graticule-projected. The DHG projection is registered via proj4 on first use.

Usage

Stack both grid systems to reproduce the sheet appearance: a fine black km grid with the orange HMN cells layered on top.

import Map from 'ol/Map';
import View from 'ol/View';
import { UniversalGraticule } from '@zwaarcontrast/ol-graticule';
import {
  DhgGridSystem,
  HmnGridSystem,
} from '@zwaarcontrast/ol-graticule-heeresgitter';

const dhg = new DhgGridSystem();
const hmn = new HmnGridSystem();

map.addLayer(new UniversalGraticule({
  gridSystem: dhg,
  style: { strokeColor: '#222', edgeLabel: true },
}));
map.addLayer(new UniversalGraticule({
  gridSystem: hmn,
  style: { strokeColor: '#d97706', cellLabel: true },
}));

You can render either grid on its own. DHG covers the full validity envelope at every zoom (zone outlines at small scales, full km grid once you zoom past maxRenderResolution). HMN only renders inside its configured resolution band.

The grids

A Wehrmacht sheet of the Deutsche Heereskarte standard (post-1942) typically carries both grids superimposed:

| Grid | Drawn in | Spacing | Purpose | |---|---|---|---| | DHG Deutsches Heeresgitter | black, fine line | 1 km on 1:50 000 | metric coordinates for artillery, navigation | | HMN Heeresmeldenetz | orange overprint | 6 km letter cells | verbal position reporting up the chain of command |

Both are derived from the same projection, so HMN cells align with DHG kilometre lines.

DHG projection (Gauß-Krüger on Bessel 1841)

| Parameter | Value | |---|---| | Reference ellipsoid | Bessel 1841 | | Projection | Gauß-Krüger (transverse Mercator) | | Strip width | 6° | | Scale factor on CM | 1.0 (no Maßstabsreduktion, unlike UTM's 0.9996) | | False easting | 500 000 m | | False northing | 0 (Hochwert = meridian arc from equator) | | Strip overlap | 30' on each side beyond the nominal 6° |

Zone numbering (Kennziffer) follows n = (L_m + 3°) / 6° where L_m is the central meridian. The inverse is L_m = n × 6° − 3°. Kennziffer 1 = CM 3°E; 6 = CM 33°E (Kolosjoki); 60 = CM 3°W.

Eastings on map sheets are written with the Kennziffer prepended: e.g. 5600 on the Owrutsch sheet = zone 5, Rechtswert 600 000 m. Inline grid ticks may show only the last two km digits (short form).

Validity envelope. The DHG was only specified for zones 55–14 (longitude −36° to +84°) and IMW rows SI–R (latitude −32° to +72°). The renderer uses these as its hard clip envelope.

HMN (planar) hierarchy

The standardised Deutsche Heereskarte (1942 onwards) prints this variant. Cells are 6 km Kleinquadrate keyed off the DHG km lattice.

| Level | Size | Labelling | Origin | |---|---|---|---| | Großquadrat | 150 km × 150 km | implicit, identified by sheet | intersection of CM with integer × 150 km Northing | | Kleinquadrat | 6 km × 6 km | letter pair AA..ZZ (25 letters, I skipped) | NW corner of Großquadrat | | Meldetrapez | 2 km × 2 km | 1..9 (3 × 3, NW→SE row-major) | NW corner of Kleinquadrat | | Arbeitstrapez | 1 km × 1 km | a..d (2 × 2, NW→SE row-major) | NW corner of Meldetrapez | | (tenths) | 100 m precision | 2 digits, east + north | SW corner of Arbeitstrapez |

Letter-pair rule. 25-letter alphabet A B C D E F G H J K L M N O P Q R S T U V W X Y Z (no I). First letter = column, ascending W → E within the Großquadrat. Second letter = row, ascending N → S.

Sub-cell layout:

Meldetrapez (2 km, inside Kleinquadrat)    Arbeitstrapez (1 km, inside Meldetrapez)
  1  2  3                                    a  b
  4  5  6                                    c  d
  7  8  9

The optional tenths suffix counts (east, north) from the SW corner of the Arbeitstrapez at 100 m precision. Canonical grammar: ([A-HJ-Z][A-HJ-Z]) ?([1-9])([a-d])?( ?\d{2})?.

Disambiguation. AA..ZZ repeats every 150 km Großquadrat, so a complete report includes the sheet number. The parseHmn API requires either an explicit grossquadrat or a near location.

HMN (geographic) hierarchy

The lat/lon-bounded variant. Sheets self-identify with a Heeresmeldenetz (geogr.) header. Cells are degree-bounded so they don't depend on a projection; the grid renders directly on any view CRS.

| Level | Size | Labelling | Origin | |---|---|---|---| | Großtrapez | 2°30′ lon × 1°40′ lat | name of settlement | (0°40′N, 0°E), stepping ±2°30′ / ±1°40′ | | Kleintrapez | 6′ lon × 4′ lat | letter pair AA..ZZ (no I) | NW corner of Großtrapez | | Meldetrapez | 2′ × 1′20″ | 1..9 (3 × 3, NW→SE row-major) | NW corner of Kleintrapez | | Arbeitstrapez | 1′ × 40″ | a..d (2 × 2, NW→SE row-major) | NW corner of Meldetrapez | | (tenths) | 6″ × 4″ | 2 digits, east + north | SW corner of Arbeitstrapez |

The anchor 0°40′N is empirical. Buchroithner & Pfahlbusch (2016) print 1°N (!), but every observed primary source fits an anchor 20′ south of that. See VALIDATION.md for the worked Romfo example and a Den Haag cross-check.

DHG options

| Option | Type | Default | What it does | |---|---|---|---| | zoneBoundary | 'tiled' | 'overlap' | 'single' | 'tiled' | Behaviour at 6° zone seams. tiled cuts hard at each meridian. overlap re-draws the 30' overlap band like wartime sheets that straddle a strip. single only renders the zone nearest the viewport centre. | | labelForm | 'long' | 'short' | 'long' | long prints the Kennziffer-prefixed full km value ("5600"). short prints only the last two digits ("00"). Wartime corners use long form; inline ticks use short. | | maxRenderResolution | number (m/px) | 2000 | Above this, only zone outlines + Kennziffer labels render. | | overviewLabelMaxResolution | number (m/px) | 6000 | Strip-boundary lines always render, but Kennziffer labels are gated to avoid clutter. | | targetScreenPx | number | 80 | Target pixel spacing between adjacent grid lines; drives the 1/2/6/30/150 km interval ladder. | | densificationPoints | number | 60 | Vertices per grid line for non-affine view projections. | | datumShift | DatumShift | Potsdam | Override the WGS 84 → Bessel-Potsdam Helmert transform. |

HMN options

| Option | Type | Default | What it does | |---|---|---|---| | maxDepth | 2 | 3 | 4 | 4 | 2 = Kleinquadrat only, 3 = + Meldetrapez, 4 = + Arbeitstrapez. | | maxRenderResolution | number (m/px) | 300 | HMN hides itself at smaller scales (DHG carries the metric grid). | | targetScreenPx | number | 80 | Pixel size at which a level subdivides into the next. | | zoneBoundary | 'tiled' | 'overlap' | 'single' | 'tiled' | Same semantics as DhgGridSystem. | | datumShift | DatumShift | Potsdam | Override the datum shift. | | densificationPoints | number | 60 | Vertices per grid line. |

Encoding and parsing

DHG: (lat, lon) to printed kilometre labels

import { encodeDhg, encodeDhgText, formatEasting, formatNorthing }
  from '@zwaarcontrast/ol-graticule-heeresgitter';

const coord = encodeDhg([69.5, 30.0]);            // Kolosjoki NW corner
// -> { kennziffer: 6, easting: 383038.., northing: 7715567.. }

formatEasting(coord);                              // -> "6383" (long form)
formatEasting(coord, { form: 'short' });           // -> "83"   (inline tick)
formatNorthing(coord);                             // -> "7715"

encodeDhgText([52.0, 28 + 20 / 60]);               // Owrutsch NW corner
// -> "5591 5763"   (zone 5, ~91 km east of CM 27°E, Hochwert ~5763 km)

Input order is [latitude, longitude]. encodeDhg picks the zone whose central meridian is nearest the longitude; pass an explicit kennziffer to force a specific zone.

HMN: (lat, lon) to letter-cell reference

import { encodeHmn, formatHmn } from '@zwaarcontrast/ol-graticule-heeresgitter';

// The Hadres sheet prints "PE 1b 52" as a worked Meldung; it resolves
// to approximately 48.509°N / 16.156°E:
const ref = encodeHmn([48.509, 16.156]);
// ref.canonical -> "PE 1b 52"
// ref.grossquadrat -> { kennziffer: 3, gx: 0, gy: 35 }
// ref.bbox -> [16.155.., 48.508.., 16.156.., 48.509..]   (100 m cell)

encodeHmn([48.509, 16.156], { depth: 2 }).canonical; // -> "PE"
encodeHmn([48.509, 16.156], { depth: 3 }).canonical; // -> "PE 1"
encodeHmn([48.509, 16.156], { depth: 4 }).canonical; // -> "PE 1b"

Reverse: parse an HMN reference back to a coordinate

Because AA..ZZ repeats every 150 km Großquadrat, parsing needs disambiguation. Pass either an explicit grossquadrat, or a near location and the library picks the closest matching Großquadrat:

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

parseHmn('PE 1b 52', { near: [48.6, 16.1] });
// -> { canonical: 'PE 1b 52',
//      kleinquadrat: 'PE', meldetrapez: 1, arbeitstrapez: 'b',
//      tenths: [5, 2], depth: 5,
//      grossquadrat: { kennziffer: 3, gx: 0, gy: 35 },
//      bbox: [16.155.., 48.508.., 16.156.., 48.509..],
//      center: [48.509.., 16.156..] }

Lenient input: case-insensitive, optional whitespace, optional sub-cell parts.

Theatres

The DHG is one global system. All Planhefte use the same projection and the same letter-cell rule, so this package needs no theatre-specific factory functions, in contrast to the Modified British System which has one factory per theatre. Only local material differs (source maps, height datums, place-name conventions). The package uses a single global Helmert (Potsdam datum); override per call via datumShift for the 50–150 m residuals between national triangulations.

What this package doesn't implement

• Luftwaffe Gradnetzmeldeverfahren (GNMV) and Jägermeldenetz (JMN). Different grids; for those, see @zwaarcontrast/ol-graticule-luftwaffe-planquadrat.
• UTM-REF / Deutscher Heeresblattschnitt, the 1944 prototype that later became MGRS. Covered by @zwaarcontrast/ol-graticule-mgrs.
• DRG (Deutsches Reichsgitter), the civilian 3°-strip predecessor.

Primary-source validation

The encoding rules are anchored to wartime Deutsche Heereskarte sheets and the explicit DHG specification in the Planheft Schweiz (OKH g 23/1, 16 March 1944). See VALIDATION.md for worked checks against the Kolosjoki, Hadres, Owrutsch, Embenskij Post, and Romfo sheets, the Planheft Schweiz world-coverage plate, and the Den Haag cross-check against an Atlantikwall sector overprint.

Sources

• Planheft Schweiz (OKH g 23/1, 16 March 1944), pages C 1–C 3: the explicit DHG projection specification.
• Buchroithner & Pfahlbusch, Geodetic grids in authoritative maps: new findings about the origin of the UTM Grid, Cartography & Geographic Information Science (2016), DOI 10.1080/15230406.2015.1128851 (open-access PDF via Austria-Forum): the explicit spec for both HMN variants, citing RdLuObdL ChAusbW VorschLmAbtRLM/LIn12 76/40.
• Powell & Mühr, Capturing the Complex Histories of German World War II Captured Maps (UC Berkeley Library): provenance for the captured-map collection.
• Map sheet images courtesy of the UC Berkeley Library, German WWII Captured Maps digital collection, https://digicoll.lib.berkeley.edu/record/105643.

License

MIT. See LICENSE.