geo/projection

WGS84 ↔ ENU coordinate conversion using proj4.

createProjection

function createProjection(
  originLat: number,
  originLon: number
): {
  toENU: (lng: number, lat: number) => [number, number]
  toLngLat: (x: number, y: number) => [number, number]
}

Creates a Transverse Mercator projection centered on (originLat, originLon).

Parameters

Name	Type	Description
originLat	number	WGS84 latitude of the ENU origin, degrees
originLon	number	WGS84 longitude of the ENU origin, degrees

Returns an object with two conversion functions:

• toENU(lng, lat) — converts a WGS84 point to [easting_m, northing_m]
• toLngLat(x, y) — converts ENU meters back to [longitude, latitude]

Example

const proj = createProjection(37.4, -122.0)

const [e, n] = proj.toENU(-122.0012, 37.4008)
// e ≈ -95.8, n ≈ 88.5

const [lng, lat] = proj.toLngLat(e, n)
// lng ≈ -122.0012, lat ≈ 37.4008

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setGlobalProjection

function setGlobalProjection(
  originLat: number,
  originLon: number
): ReturnType<typeof createProjection>

Creates a projection and stores it as the module-level singleton. Returns the same object as createProjection.

Called once during New Project creation and once during import (to restore the origin from the proto header).

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getGlobalProjection

function getGlobalProjection(): ReturnType<typeof createProjection> | null

Returns the current global projection, or null if not yet initialized.

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lngLatToENU

function lngLatToENU(lng: number, lat: number): PointENU

Convenience wrapper around the global projection's toENU. Returns a PointENU object:

{ x: easting_m, y: northing_m, z: 0 }

Used extensively in buildBaseMap.ts to convert each GeoJSON coordinate.

Throws if no global projection has been set via setGlobalProjection.