Round every heading readout through one shared helper

The transit, ALPR, vessel, CCTV and flight/military context fixes each
wrapped 359.5° to north with an inline Math.round(x) % 360. They now call
roundHeadingDegrees in src/data/headingDegrees.js, which also wraps negative
and multi-turn bearings. normalizeHeading moves there with it, and
cockpitMath re-exports it so existing imports keep working. It now adds a
turn only to a negative remainder, so a bearing just under half a degree
keeps its precision.

The awareness, Local ADS-B, cockpit wind, cockpit heading and Street Level
readouts use the same helper. The Cockpit's TRACK ACQUIRED signal rounded
without wrapping and could read COURSE 360°; it now uses
formatHeadingReadout, which shows --- for a track that is not finite.

src/layers/alpr/visuals.js

@@ -5,6 +5,7 @@ import {
   DIRECTION_CONE_HALF_ANGLE_DEG,
   MARKER_SCALE_BY_DISTANCE,
 } from './policy.js';
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
 
 /**
  * Badge scale at a camera distance, matching Cesium's NearFarScalar for the
@@ -49,9 +50,8 @@ export function alprLabelDetails(record, source) {
   const details = [
     sourceName === 'OpenStreetMap' ? 'OSM MAPPED' : `Source: ${sourceName}`,
   ];
-  // Wrap after rounding: 359.6° rounds to 360°, which is north.
   if (Number.isFinite(record.directionDeg))
-    details.push(`DIRECTION ${Math.round(record.directionDeg) % 360}°`);
+    details.push(`DIRECTION ${roundHeadingDegrees(record.directionDeg)}°`);
   const equipment = [
     ...new Set(
       [record.manufacturer, record.operator, record.cameraType]

src/layers/awareness/presentation.js

@@ -1,3 +1,5 @@
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
+
 /**
  * Format a compass direction for the awareness overlay.
  * @param {number} degrees
@@ -5,6 +7,5 @@
  */
 export function formatAwarenessDirection(degrees) {
   if (!Number.isFinite(degrees)) return '—';
-  const normalized = ((degrees % 360) + 360) % 360;
-  return String(Math.round(normalized) % 360).padStart(3, '0');
+  return String(roundHeadingDegrees(degrees)).padStart(3, '0');
 }

src/layers/cctv/headingConfidence.js

@@ -1,4 +1,5 @@
 import { t } from '../../i18n/index.js';
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
 
 /**
  * @module headingConfidence
@@ -44,8 +45,7 @@ export function isHeadingEstimated(camera) {
  * @returns {string}
  */
 export function headingHudToken(camera) {
-  // 359.5° and above rounds to north; modulo keeps it from printing 360°.
-  const hdg = Math.round(Number(camera?.headingDeg) || 0) % 360;
+  const hdg = roundHeadingDegrees(Number(camera?.headingDeg)) ?? 0;
   return isHeadingEstimated(camera)
     ? t('HDG {value}° (ESTIMATED)', { value: hdg })
     : t('HDG {value}°', { value: hdg });

src/layers/flights/tracking.js

@@ -24,6 +24,7 @@ import {
   TRAIL_COLOR,
   CYAN_TRANSPARENT,
 } from './policy.js';
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
 
 export function createTracking({
   flightState,
@@ -125,9 +126,8 @@ export function createTracking({
         speed: Number.isFinite(described.velocityMps)
           ? `${Math.round(described.velocityMps * 1.944)} kt`
           : '',
-        // 359.5° and above rounds to north; modulo keeps it from reading 360°.
         heading: Number.isFinite(described.track)
-          ? `${Math.round(described.track) % 360}°`
+          ? `${roundHeadingDegrees(described.track)}°`
           : '',
         route: route || '',
         icao24,

src/layers/localAdsb/card.js

@@ -1,6 +1,7 @@
 import { AIRCRAFT_CLASS_LABELS } from '../../data/aircraftClass.js';
 import { formatNumber, t, tn } from '../../i18n/index.js';
 import { BAND_LABELS, LOCAL_ADSB_COLOR, SOURCE_LABELS } from './policy.js';
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
 
 const DASH = '—';
 
@@ -152,7 +153,7 @@ export function localAdsbCardModel(
       t('ALT {altitude} FT · GS {speed} KT · TRK {track}', {
         altitude: grouped(altitude),
         speed: speed === null ? DASH : speed,
-        track: track === null ? DASH : `${track % 360}°`,
+        track: track === null ? DASH : `${roundHeadingDegrees(track)}°`,
       }),
       vertical === null
         ? t('V/S {rate}', { rate: DASH })

src/layers/military/tracking.js

@@ -25,6 +25,7 @@ import {
   AMBER_TRANSPARENT,
   TRACKED_ICON_COLOR,
 } from './policy.js';
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
 
 export function createTracking({
   flightState,
@@ -119,9 +120,8 @@ export function createTracking({
         speed: Number.isFinite(described.velocityMps)
           ? `${Math.round(described.velocityMps * 1.944)} kt`
           : '',
-        // 359.5° and above rounds to north; modulo keeps it from reading 360°.
         heading: Number.isFinite(described.track)
-          ? `${Math.round(described.track) % 360}°`
+          ? `${roundHeadingDegrees(described.track)}°`
           : '',
         icao24,
         // Honesty cue: the contact is coasting on dead reckoning, so the

src/layers/transit/policy.js

@@ -9,6 +9,7 @@ import {
   transitRouteLabel,
 } from '../../data/transitFeeds.js';
 import { displayMotion, playbackPosition } from './movement.js';
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
 
 export const TRANSIT_SELECTED_OVERLAY_SOURCE_ID = 'transit-selected';
 export const TRANSIT_SELECTED_OVERLAY_SOURCE_OPTIONS = Object.freeze({
@@ -405,11 +406,10 @@ export function buildTransitSelectionCopy(
     reportedMotion.push(
       t('reported {speed} km/h', { speed: Math.round(record.speedMps * 3.6) }),
     );
-  // 359.5° and above rounds to north; modulo keeps it from printing 360°.
   if (Number.isFinite(record.bearing))
     reportedMotion.push(
       t('reported hdg {heading}°', {
-        heading: Math.round(record.bearing) % 360,
+        heading: roundHeadingDegrees(record.bearing),
       }),
     );
   // The operator's own claim, kept as a REPORT rather than as the live state.

src/layers/vessels/cards.js

@@ -4,6 +4,7 @@ import {
   normalizeVesselType,
 } from '../../data/vesselLabels.js';
 import { formatNumber, t } from '../../i18n/index.js';
+import { roundHeadingDegrees } from '../../data/headingDegrees.js';
 
 export function createCards({
   vesselState,
@@ -55,10 +56,8 @@ export function createCards({
     if (record.speed !== null && record.speed !== undefined)
       parts.push(formatSpeed(record.speed));
     const direction = record.heading ?? record.course;
-    // A course of 359.5° and above rounds to north; modulo keeps it from
-    // printing 360°. The selected card and the HUD wrap the same way.
     if (Number.isFinite(direction))
-      parts.push(`${Math.round(direction) % 360}°`);
+      parts.push(`${roundHeadingDegrees(direction)}°`);
     return {
       id: vesselOverlayEntryId(record),
       actionable: Boolean(record?.mmsi),
@@ -89,7 +88,9 @@ export function createCards({
       [
         vesselTypeShort(record) || t('VESSEL'),
         formatSpeed(record.speed),
-        Number.isFinite(direction) ? `${Math.round(direction) % 360}°` : '--°',
+        Number.isFinite(direction)
+          ? `${roundHeadingDegrees(direction)}°`
+          : '--°',
       ].join(' · '),
     ];
     const destination = String(record.destination || '').trim();
@@ -179,7 +180,7 @@ export function createCards({
 
   function formatHeading(heading) {
     return t('{heading}DEG', {
-      heading: Number.isFinite(heading) ? Math.round(heading) % 360 : '--',
+      heading: roundHeadingDegrees(heading) ?? '--',
     });
   }