proj4js 坐标转换

2021-11-04 04:44:16

一、概述

Proj4js 是一个开源的 JavaScript 库，用于将点坐标从一个坐标系转换到另一个坐标系，包括基准转换。

git代码库地址：https://github.com/proj4js/proj4js

另一个坐标系在线查询和坐标转换地址：https://epsg.io/

在PostGIS中有一个表 spatial_ref_sys ，可以查询所有的坐标系信息。

在Geoserver中也有所有坐标系的信息。在ArcGIS中也有。

以下介绍在node中使用proj4，以及在Cesium三维开发中使用。

二、node中使用Proj4

1、引入库，npm install proj4

2、引用库，const proj4 = require(‘proj4‘)

3、转换方法，proj4(fromProjection, toProjection, [x, y])

4、坐标系举例说明

EPSG:4549 CGCS2000 / 3-degree Gauss-Kruger CM 120E

2000大地坐标系，3度分带，高斯克吕格投影，*经线120。

如果坐标是加了带号的，就用4528。具体看需要转换的数据坐标。加了带号的X坐标前面两位就是带号。

东西向X坐标不加带号6位数（坐标向东偏移，了500km，因此*子午线的X坐标就是500000，加了带号就是365000000），加了带号8位数。南北方向7位数

EPSG:4528 CGCS2000 / 3-degree Gauss-Kruger zone 40

3度带*经线=3乘以带号

5、代码，在下面的代码中实现将点坐标从CGCS2000坐标系EPSG:4549转换为WGS84坐标系

函数convert111_和convert111结果相同。因为proj4函数可以传入坐标系的wkt，也可以传入proj.4。

/*
 * @Author: 苹果园dog
 * @Date: 2021-07-01 11:48:07
 * @LastEditTime: 2021-07-01 17:44:56
 * @LastEditors: Please set LastEditors
 * @Description: In User Settings Edit
 * @FilePath: 
 */
const proj4 = require(‘proj4‘);
function convert111_(x, y) {
  const fromProjection = `PROJCS["CGCS2000 / 3-degree Gauss-Kruger CM 120E",GEOGCS["China Geodetic Coordinate System 2000",DATUM["China_2000",SPHEROID["CGCS2000",6378137,298.257222101,AUTHORITY["EPSG","1024"]],AUTHORITY["EPSG","1043"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4490"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",120],PARAMETER["scale_factor",1],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","4549"]]
  `;
  const toProjection = `GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG", "6326"]], PRIMEM["Greenwich", 0, AUTHORITY["EPSG", "8901"]],
        UNIT["degree", 0.0174532925199433, AUTHORITY["EPSG", "9122"]], AUTHORITY["EPSG", "4326"]]`;
  const newCoordinates = proj4(fromProjection, toProjection, [x, y]);
  return newCoordinates;
}

function convert111(x, y) {
  const fromProjection = `+proj=tmerc +lat_0=0 +lon_0=120 +k=1 +x_0=500000 +y_0=0 +ellps=GRS80 +units=m +no_defs`;
  const toProjection = `+proj=longlat +datum=WGS84 +no_defs`;
  const newCoordinates = proj4(fromProjection, toProjection, [x, y]);
  return newCoordinates;
}

module.exports = {
  convert111: convert111
}

6、坐标转换测试

三、Cesium中使用Proj4

由于Cesium三维球默认是WGS84的，要想加载一些CGCS2000坐标系的一些矢量文件。

比如geojson，kml等，需要在加载数据的时候动态转换坐标。

以下介绍加载2000坐标系的Geojson方法。

在下面的代码中实现将点坐标从CGCS2000坐标系EPSG:4524转换为WGS84坐标系。

/*
 * @Author: 苹果园dog
 * @Date: 2021-04-12 14:42:01
 * @LastEditTime: 2021-04-12 14:46:41
 * @LastEditors: Please set LastEditors
 * @Description: In User Settings Edit
 * @FilePath: 
 */
import { default as proj4 } from "proj4";

Cesium.GeoJsonDataSource.crsNames[
  "urn:ogc:def:crs:EPSG::4524"
] = Cesium.GeoJsonDataSource.crsNames["EPSG:4524"] = function(coordinates) {
  const fromProj = `PROJCS["CGCS2000 / 3-degree Gauss-Kruger zone 36", 
        GEOGCS["China Geodetic Coordinate System 2000", 
          DATUM["China 2000", 
            SPHEROID["CGCS2000", 6378137.0, 298.257222101, AUTHORITY["EPSG","1024"]], 
            AUTHORITY["EPSG","1043"]], 
          PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]], 
          UNIT["degree", 0.017453292519943295], 
          AXIS["Geodetic longitude", EAST], 
          AXIS["Geodetic latitude", NORTH], 
          AUTHORITY["EPSG","4490"]], 
        PROJECTION["Transverse_Mercator", AUTHORITY["EPSG","9807"]], 
        PARAMETER["central_meridian", 108.0], 
        PARAMETER["latitude_of_origin", 0.0], 
        PARAMETER["scale_factor", 1.0], 
        PARAMETER["false_easting", 36500000.0], 
        PARAMETER["false_northing", 0.0], 
        UNIT["m", 1.0], 
        AXIS["Easting", EAST], 
        AXIS["Northing", NORTH], 
        AUTHORITY["EPSG","4524"]]`;
  const toProj = `GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG", "6326"]], PRIMEM["Greenwich", 0, AUTHORITY["EPSG", "8901"]],
        UNIT["degree", 0.0174532925199433, AUTHORITY["EPSG", "9122"]], AUTHORITY["EPSG", "4326"]]`;

  const x = coordinates[0];
  const y = coordinates[1];

  const newCoordinates = proj4(fromProj, toProj, [x, y]);
  return Cesium.Cartesian3.fromDegrees(newCoordinates[0], newCoordinates[1], 0);
};

proj4js 坐标转换

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