China's Projection for OpenLayers

Author: wkgreat

Projection Supported

Introduction

GCJ02 is a coordinate systems often used in China. Strictly speaking, it is a confidential algorithm for encrypting geopoints. After processing by GCJ02 algorithm, the point defined in WGS84 will be deviated on web map visually. This module defines the GCJ02 as a Projection of openlayers, likewise EPSG:4326 and EPSG:3857

💡From version 1.0.3 also support typescript.

Install:

npm install ol-proj-ch

Import:

by import olpjch, the olpjch is defined as a container for all supported projections in this module.
by import {xxx} from 'ol-proj-ch', import the pertinent projection you want.

import olpjch from 'ol-proj-ch'

/* GCJ02 */
const GCJ02 = olpjch.GCJ02
const code = GCJ02.CODE
//...

/* BD09 */
const BD09 = olpjch.BD09
const code = BD09.CODE

//or import GCJ02, BD09 or others
import {GCJ02} from 'ol-proj-ch'
import {BD09} from 'ol-proj-ch'
const code1 = GCJ02.CODE    //the code of GCJ02
const code2 = BD09.CODE     //the code of BD09

Usage:

💡 here use GCJ02 to make exmaples.

• transform a coordinate from gcj02 to wgs84(EPSG:4326)

import {GCJ02} from 'ol-proj-ch'
import {transform} from 'ol/proj'
const coords = [117.0,32.0];
const newCoords = transform(coords, GCJ02.CODE, "EPSG:4326");

likewise, use transform([coords, "EPSG:4326", GCJ02.CODE) from wgs84 to gcj02

• transform a coordinate from gcj02 to EPSG:3857

import {GCJ02} from 'ol-proj-ch'
import {transform} from 'ol/proj'
const coords = [117.0,32.0];
const newCoords = transform(coords, GCJ02.CODE, "EPSG:3857");

likewise, use transform([coords, "EPSG:3857", GCJ02.CODE) from EPSG:3827 to gcj02

• eg: create feature from geojson data of GCJ02

import {GCJ02} from 'ol-proj-ch'
import {GeoJSON} from "ol/format";

//geojson data pretend coordinates are in GCJ02
const data = {
   "type": "Feature",
   "geometry": {
      "type": "Point",
      "coordinates": [125.6, 10.1]
   },
   "properties": {
      "name": "Dinagat Islands"
   }
};

const format = new GeoJSON();
let feature = format.readFeature(data, {
   dataProjection: GCJ02.CODE,
   featureProjection: "EPSG:3857"
});
//... then add feature to layer and then add to map

• eg: visulaize vector data from wkt with gcj02 data projection

import {GCJ02} from 'ol-proj-ch'
import WKT from "ol/format/WKT";

//WKT data
const data = `POINT (125.6 10.1)`;

const format = new WKT();
let feature = format.readFeature(data, {
   dataProjection: GCJ02.CODE,
   featureProjection: "EPSG:3857"
});
//... then add feature to layer and then add to map