geotile_sdk/src/SRS.js

A tile sdk for Cloud Optimised Geotiff and shapefile

/*
 * @Description: SRS convertor (spatial reference system ,SRS) 空间参考系的转换
 * @Author: luojun1
 * @Date: 2021-10-21 17:25:12
 * @LastEditTime: 2021-12-02 16:51:19
 */

function tile2X (x, z) {
  return (x / Math.pow(2, z) * 2 - 1) * 6378137.0 * Math.PI
}

function tile2Y (y, z) {
  return (1 - 2 * y / Math.pow(2, z)) * 6378137.0 * Math.PI
}

// tile to bbox on web mercator
function tile2BBox (tile, tile2) {
  if (!tile2) {
    tile2 = [tile[0] + 1, tile[1] + 1]
  }
  var e = tile2X(tile2[0], tile[2])
  var w = tile2X(tile[0], tile[2])
  var s = tile2Y(tile2[1], tile[2])
  var n = tile2Y(tile[1], tile[2])
  return [w, s, e, n]
}

const r2d = 180 / Math.PI

function tile2lon (x, z) {
  return (x / Math.pow(2, z) * 360 - 180)
}

function tile2lat (y, z) {
  var n = Math.PI - 2 * Math.PI * y / Math.pow(2, z)
  return (r2d * Math.atan(0.5 * (Math.exp(n) - Math.exp(-n))))
}

// tile to bbox on WGS84
function tile2BBox84 (tile) {
  var e = tile2lon(tile[0] + 1, tile[2])
  var w = tile2lon(tile[0], tile[2])
  var s = tile2lat(tile[1] + 1, tile[2])
  var n = tile2lat(tile[1], tile[2])
  return [w, s, e, n]
}

//  WGS84 to web mercator
function WGS84To3857 (lng, lat) {
  var out = []
  out[0] = 6378137.0 * (Math.PI * lng / 180)
  if (lat <= -90) {
    out[1] = -20037508.3427892
  } else if (lat >= 90) {
    out[1] = 20037508.3427892
  } else {
    out[1] = 6378137.0 * Math.log(Math.tan((Math.PI * 0.25) + (0.5 * (Math.PI * lat / 180))))
  };
  return out
};

module.exports = {
  tile2BBox,
  tile2BBox84,
  WGS84To3857
}