mirror of
https://github.com/mauriceboe/TREK.git
synced 2026-10-22 06:56:35 +00:00
A1phaN
80 lines
3.4 KiB
TypeScript
80 lines
3.4 KiB
TypeScript
import L from 'leaflet'
|
|
import { gcj02ToWgs84, wgs84ToGcj02 } from '@trek/shared'
|
|
|
|
/**
|
|
* A Leaflet CRS that draws WGS-84 coordinates on GCJ-02 tiles.
|
|
*
|
|
* Amap's raster tiles are rendered in GCJ-02 — the datum Chinese law requires
|
|
* published maps to use — while every coordinate in TREK is WGS-84: the database
|
|
* columns, the search results, the routes from OSRM, an imported GPX track. Put
|
|
* one on the other untouched and every marker sits a few hundred metres from the
|
|
* building it names, which around a city block is the wrong street.
|
|
*
|
|
* The fix could live in three places, and two of them are worse:
|
|
*
|
|
* - Converting each marker at the call site means every component that draws
|
|
* anything on a map has to know which basemap is loaded — MapView,
|
|
* JourneyMap, CollectionMap, the cluster group, the route polylines, the
|
|
* bounds fitting, the click handler that turns a pixel back into a place.
|
|
* Miss one and it is off by 300 m with no error anywhere.
|
|
* - A constant offset is not a fix at all: the shift is a function of position,
|
|
* ranging from roughly 100 m to 800 m across the country.
|
|
*
|
|
* So it goes into the projection, which is the one place every coordinate
|
|
* already passes through. `project` shifts WGS-84 → GCJ-02 before the standard
|
|
* Web Mercator maths, `unproject` shifts back, and everything above it —
|
|
* markers, polylines, `getBounds`, `containerPointToLatLng` — keeps speaking
|
|
* WGS-84 without knowing this exists.
|
|
*
|
|
* Everything else is inherited from EPSG3857 on purpose: Amap's tile grid IS
|
|
* standard Web Mercator (same zoom levels, same 256 px tiles, same origin), so
|
|
* the scale and the transformation must not change. Only the datum does.
|
|
* `distance()` also stays as it is and stays correct, because it is handed
|
|
* WGS-84 latitudes.
|
|
*/
|
|
function buildCrs(): L.CRS {
|
|
const mercator = L.Projection.SphericalMercator
|
|
const projection: L.Projection = {
|
|
project(latlng: L.LatLng): L.Point {
|
|
const gcj = wgs84ToGcj02(latlng.lat, latlng.lng)
|
|
return mercator.project(L.latLng(gcj.lat, gcj.lng))
|
|
},
|
|
unproject(point: L.Point): L.LatLng {
|
|
const gcj = mercator.unproject(point)
|
|
const wgs = gcj02ToWgs84(gcj.lat, gcj.lng)
|
|
return L.latLng(wgs.lat, wgs.lng)
|
|
},
|
|
bounds: mercator.bounds,
|
|
}
|
|
return L.Util.extend({}, L.CRS.EPSG3857, { code: 'TREK:GCJ02', projection }) as L.CRS
|
|
}
|
|
|
|
/**
|
|
* Built on first use, not at import.
|
|
*
|
|
* Reading `L.Projection.SphericalMercator` while the module graph loads means
|
|
* every importer of MapView has to have a fully-formed Leaflet — which the map
|
|
* component tests deliberately do not, they mock it down to the handful of
|
|
* exports they assert on. A basemap nobody selected should not be able to break
|
|
* an unrelated test file, or a build, by existing.
|
|
*/
|
|
let cached: L.CRS | null = null
|
|
|
|
export function getCrsGcj02(): L.CRS {
|
|
if (!cached) cached = buildCrs()
|
|
return cached
|
|
}
|
|
|
|
/**
|
|
* The CRS a map should use for a given basemap.
|
|
*
|
|
* Returning `undefined` rather than `L.CRS.EPSG3857` matters: passing a `crs`
|
|
* option to a MapContainer is what pins it, and Leaflet cannot change a map's
|
|
* CRS after construction. Handing back undefined lets the component omit the
|
|
* prop entirely for the 99% of installs on a WGS-84 basemap, which keeps their
|
|
* map byte-identical to what it was.
|
|
*/
|
|
export function crsForBasemap(isGcj02: boolean): L.CRS | undefined {
|
|
return isGcj02 ? getCrsGcj02() : undefined
|
|
}
|