投影 Projection

Projection 类提供坐标参考系统（CRS）之间的坐标转换能力，支持自定义投影定义。

Projection

构造函数

class Projection {
  readonly id: string;

  constructor(id: string, def: string);
}

参数

参数	类型	说明
id	string	投影标识符（如 'EPSG:4326'）
def	string	投影定义字符串（Proj4 格式）

方法

方法	参数	返回值	说明
transform(coord, targetCRS)	coord: Coordinate, targetCRS: string	Coordinate	坐标转换
transformMany(coords, targetCRS)	coords: Coordinate[], targetCRS: string	Coordinate[]	批量坐标转换
forward(coord)	coord: Coordinate	Pixel	地理坐标 -> 投影像素
inverse(pixel)	pixel: Pixel	Coordinate	投影像素 -> 地理坐标
getUnitsPerMeter()	—	number	获取每米对应的投影单位数
equals(o)	o: Projection	boolean	是否为同一投影

---

示例

创建投影

import { Projection } from '@gmap/standard';

// WGS84 (EPSG:4326)
const wgs84 = new Projection(
  'EPSG:4326',
  '+proj=longlat +datum=WGS84 +no_defs'
);

// Web Mercator (EPSG:3857)
const webMercator = new Projection(
  'EPSG:3857',
  '+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs'
);

// CGCS2000 (EPSG:4490)
const cgcs2000 = new Projection(
  'EPSG:4490',
  '+proj=longlat +datum=CGCS2000 +no_defs'
);

坐标转换

import { Projection } from '@gmap/standard';

const wgs84 = new Projection('EPSG:4326', '+proj=longlat +datum=WGS84');
const webMercator = new Projection('EPSG:3857', '+proj=merc ...');

// WGS84 -> Web Mercator
const mercatorCoord = wgs84.transform([116.397, 39.908], 'EPSG:3857');
console.log(mercatorCoord); // [12946768.64, 4851854.47] (约)

// Web Mercator -> WGS84
const wgs84Coord = webMercator.transform([12946768.64, 4851854.47], 'EPSG:4326');
console.log(wgs84Coord); // [116.397, 39.908] (约)

批量转换

const wgs84 = new Projection('EPSG:4326', '+proj=longlat +datum=WGS84');

const coords = [
  [116.397, 39.908],
  [116.407, 39.918],
  [116.417, 39.928],
];

const mercatorCoords = wgs84.transformMany(coords, 'EPSG:3857');
console.log(mercatorCoords); // 3 个 Web Mercator 坐标

前向/反向投影

const wgs84 = new Projection('EPSG:4326', '+proj=longlat +datum=WGS84');

// 地理坐标 -> 像素
const pixel = wgs84.forward([116.397, 39.908]);
console.log(pixel); // [116.397, 39.908] (原始坐标即像素)

// 像素 -> 地理坐标
const coord = wgs84.inverse([100, 200]);
console.log(coord); // [100, 200]

比较投影

const wgs84a = new Projection('EPSG:4326', '+proj=longlat +datum=WGS84');
const wgs84b = new Projection('EPSG:4326', '+proj=longlat +datum=WGS84');
const mercator = new Projection('EPSG:3857', '+proj=merc ...');

console.log(wgs84a.equals(wgs84b)); // true
console.log(wgs84a.equals(mercator)); // false

获取单位比率

const wgs84 = new Projection('EPSG:4326', '+proj=longlat +datum=WGS84');
const webMercator = new Projection('EPSG:3857', '+proj=merc ...');

console.log(wgs84.getUnitsPerMeter());      // ~0.00000899 (度/米)
console.log(webMercator.getUnitsPerMeter()); // 1 (米/米)

---

与 ProjectionUtils 配合

Projection 类可以与 ProjectionUtils 命名空间配合使用，实现全局投影管理。

import { Projection, ProjectionUtils } from '@gmap/standard';

// 注册自定义投影
const myProj = new Projection('EPSG:4547', '+proj=tmerc +lat_0=0 +lon_0=117 ...');
ProjectionUtils.register('EPSG:4547', myProj);

// 查询已注册投影
const proj = ProjectionUtils.get('EPSG:4547');
console.log(proj?.id); // 'EPSG:4547'

// 列出所有投影
const all = ProjectionUtils.list();
console.log(all); // ['EPSG:4547', ...]

// 检查是否支持
const supported = ProjectionUtils.isSupported('EPSG:4547'); // true

---

常用投影定义

标识	名称	Proj4 定义
EPSG:4326	WGS 84	+proj=longlat +datum=WGS84 +no_defs
EPSG:3857	Web Mercator	+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs
EPSG:4490	CGCS 2000	+proj=longlat +datum=CGCS2000 +no_defs
EPSG:4547	CGCS 2000 / 3-degree Gauss-Kruger zone 39	+proj=tmerc +lat_0=0 +lon_0=117 +k=1 +x_0=39500000 +y_0=0 +datum=CGCS2000 +units=m +no_defs