3857 Mercator coordinate system converted to 4326 (WGS84) longitude and latitude coordinates

mercatorTolonlat(mercator) {
    
  var lonlat = [0, 0]
  var x = mercator[0] / 20037508.34 * 180
  var y = mercator[1] / 20037508.34 * 180
  y = 180 / Math.PI * (2 * Math.atan(Math.exp(y * Math.PI / 180)) - Math.PI / 2)
  lonlat[0] = x
  lonlat[1] = y
  return lonlat
}

Geographic coordinate system 4326– Projection coordinate system 3857/2436

Spatial reference coordinate system query website ：https://spatialreference.org/ and http://epsg.io/

EPSG:4326 (WGS84) Geographic coordinate system ,WGS84 It is the most popular geographical coordinate system at present . In the world , Each coordinate system is assigned a EPSG Code ,EPSG:4326 Namely WGS84 Code for .
GPS Is based on WGS84 Of , So usually the coordinate data we get is WGS84 Of . Generally, when storing data , Still press WGS84 Storage .

EPSG:3857 (Pseudo-Mercator) Pseudo Mercator projection , Also known as the sphere Mercator ,Web Mercator. It's based on the Mercator projection , hold WGS84 The coordinate system is projected onto the square .

EPSG:2436, The projection coordinate system of Beijing ;
The East-West range of Beijing ：Beijing: 115.7°E - 117.4°E;
Beijing 1954 / 3-degree Gauss-Kruger CM 117E (Google it);
WGS84 Bounds: 115.5000, 22.6600, 118.5000, 49.8800;
Projected Bounds: 345818.6654, 2507707.7737, 654181.3346, 5528676.1748;
Scope: Large scale topographic mapping, cadastral and engineering survey.;
Last Revised: July 22, 2006;
Area: China - 115.5°E to 118.5°E.

Inquiry and Beijing / The coordinate system related to China

SELECT * FROM spatial_ref_sys WHERE srtext ~* 'beijing';

SELECT * FROM spatial_ref_sys WHERE srtext ~* 'china';

SELECT ST_AsText(ST_Transform(ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,743265 2967450,743265.625 2967416,743238 2967416))',2249),4326)) As wgs_geom;

SELECT ST_AsEWKT(ST_Transform(ST_GeomFromEWKT('SRID=2249;CIRCULARSTRING(743238 2967416 1,743238 2967450 2,743265 2967450 3,743265.625 2967416 3,743238 2967416 4)'),4326));