Coordinate System

Apollo HD maps use ENU (East-North-Up) coordinates in meters, with a user-defined local origin. The editor stores all geometry in WGS84 longitude/latitude (GeoJSON standard) and converts to ENU only at export time.

WGS84 (editor storage)

All LaneFeature, JunctionFeature, and other editor types hold GeoJSON Feature objects whose coordinates are [longitude, latitude] pairs in WGS84.

Advantages:

• MapLibre GL natively renders WGS84 GeoJSON
• turf.js functions (distance, offset, intersection) operate on WGS84 directly
• No precision loss from repeated ENU↔WGS84 conversions during editing

ENU (Apollo export format)

Apollo's PointENU type is:

message PointENU {
  double x = 1;  // East, meters
  double y = 2;  // North, meters
  double z = 3;  // Up, meters (default 0 for 2D maps)
}

All coordinates in base_map.bin and sim_map.bin are in ENU relative to the project origin.

Projection

The editor uses a Transverse Mercator projection centered on the project origin, via proj4:

const projStr =
  `+proj=tmerc +lat_0=${originLat} +lon_0=${originLon}` + ` +k=1 +ellps=WGS84 +no_defs`

This matches the projection string Apollo writes to MapHeader.projection.proj.

API

import { createProjection, setGlobalProjection, lngLatToENU } from './geo/projection'

// Create a projection for a specific origin
const proj = createProjection(37.4, -122.0)

// WGS84 → ENU
const [easting, northing] = proj.toENU(-122.0012, 37.4008)
// → approximately [95.8, 88.5]

// ENU → WGS84
const [lng, lat] = proj.toLngLat(95.8, 88.5)
// → approximately [-122.0012, 37.4008]

Global projection singleton

During a session, setGlobalProjection(lat, lon) stores the active projection. lngLatToENU(lng, lat) uses this singleton, so the export functions don't need to pass projection objects through every call.

setGlobalProjection(37.4, -122.0)
const enu = lngLatToENU(-122.0012, 37.4008)
// → { x: 95.8, y: 88.5, z: 0 }

Accuracy

Transverse Mercator distortion is negligible for HD map areas:

Distance from origin	Linear error
1 km	< 0.1 mm
10 km	< 1 cm
50 km	~2.5 cm
100 km	~10 cm

For city-scale maps (< 20 km across), ENU precision exceeds what mapbox-gl-draw can represent anyway (limited by float64 in GeoJSON).

Coordinate frame in exports

The MapHeader proto records the origin:

header {
  version: "1.0.0"
  date: "2026-02-19"
  projection {
    proj: "+proj=tmerc +lat_0=37.4 +lon_0=-122.0 +k=1 +ellps=WGS84 +no_defs"
  }
}

Apollo modules read this string to initialize their own proj4 projection, so the ENU → WGS84 conversion is exact when loading the map in Dreamview or the planning module.

z-coordinate

All exported PointENU.z values are 0. Apollo Map Studio is a 2D editor. For maps with elevation (highway overpasses, tunnels), you would need to post-process the exported base_map.bin and set z values externally.