China’s Projection for OpenLayers

Author: wkgreat

Projection Supported

Document

https://wkgreat.github.io/ol-proj-ch/

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:

```shell script
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.  
```javascript
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
  ```javascript
  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
```javascript
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