摘要：根據(jù)該瓦片和計算出的行列號，即可取得鼠標(biāo)點擊位置的像素值。指定級別緯度對應(yīng)的像素行號像素坐標(biāo)轉(zhuǎn)瓦片行列號像素坐標(biāo)轉(zhuǎn)瓦片行列號

import turf from "turf"
export default {
  TILE_SIZE: 256,
  /*
  * 獲取指定級別的瓦片數(shù)目
  */
  _getMapSize(level) {
    return Math.pow(2, level);
  },
  /**
     * Convert a longitude coordinate (in degrees) to the tile X number at a
     * certain zoom level.經(jīng)度轉(zhuǎn)瓦片列號
     * @param longitude
     *            the longitude coordinate that should be converted.
     * @param zoom
     *            the zoom level at which the coordinate should be converted.
     * @return the tile X number of the longitude value.
  */
   longitudeToTileX(longitude, zoom) {
       let px = this.longitudeToPixelX(longitude, zoom);
       return this.pixelXToTileX(px, zoom);
   },
   /**
      * Convert a latitude coordinate (in degrees) to a tile Y number at a
      * certain zoom level.緯度轉(zhuǎn)瓦片行號
      * @param latitude
      *            the latitude coordinate that should be converted.
      * @param zoom
      *            the zoom level at which the coordinate should be converted.
      * @return the tile Y number of the latitude value.
   */
   latitudeToTileY(latitude, zoom) {
       let py = this.latitudeToPixelY(latitude, zoom);
       return this.pixelYToTileY(py, zoom);
   },
/**
     * Convert a latitude coordinate (in degrees) to a pixel Y coordinate at a
     * certain zoom level.經(jīng)緯度坐標(biāo)(緯度)轉(zhuǎn)屏幕像素坐標(biāo)(Y)
     *
     * @param latitude
     *            the latitude coordinate that should be converted.
     * @param zoom
     *            the zoom level at which the coordinate should be converted.
     * @return the pixel Y coordinate of the latitude value.
     */
    latitudeToPixelY(latitude, zoom) {
        let sinLatitude = Math.sin(latitude * Math.PI / 180);
        return (0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI)) * (this.TILE_SIZE << zoom);
    },
    /**
     * Convert a longitude coordinate (in degrees) to a pixel X coordinate at a
     * certain zoom level.經(jīng)緯度坐標(biāo)(經(jīng)度)轉(zhuǎn)屏幕像素坐標(biāo)(X)
     *
     * @param longitude
     *            the longitude coordinate that should be converted.
     * @param zoom
     *            the zoom level at which the coordinate should be converted.
     * @return the pixel X coordinate of the longitude value.
     */
    longitudeToPixelX(longitude, zoom) {
        return (longitude + 180) / 360 * (this.TILE_SIZE << zoom);
    },
   /*
   * 指定級別下，將宏觀上的經(jīng)度轉(zhuǎn)換為對應(yīng)列上的瓦片的像素矩陣列號(微觀)
     例如：鼠標(biāo)點擊地圖，鼠標(biāo)位置在點擊的瓦片內(nèi)的行列號(即使像素行列號)。根據(jù)該瓦片(png)和計算出的行列號，即可取得鼠標(biāo)點擊位置的像素值。
  */
  _lngToPixelX(longitude, level) {
    let x = (longitude + 180) / 360;
    let pixelX = Math.floor(x * this._getMapSize(level) * 256 % 256);
    return pixelX;
  },
  /*
  * 指定級別緯度對應(yīng)的像素行號
  */
  _latToPixelY(latitude, level) {
    let sinLatitude = Math.sin(latitude * Math.PI / 180);
    let y = 0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);
    let pixelY = Math.floor(y * this._getMapSize(level) * 256 % 256);
    return pixelY;
  },
  /**
     * Convert a pixel X coordinate to the tile X number.
     * 像素坐標(biāo)X轉(zhuǎn)瓦片行列號X
     * @param pixelX
     *            the pixel X coordinate that should be converted.
     * @param zoom
     *            the zoom level at which the coordinate should be converted.
     * @return the tile X number.
   */
    pixelXToTileX(pixelX, zoom) {
        return Math.floor(Math.min(Math.max(pixelX / this.TILE_SIZE, 0), Math.pow(2, zoom) - 1));
    },
   /**
     * Converts a pixel Y coordinate to the tile Y number.
     * 像素坐標(biāo)Y轉(zhuǎn)瓦片行列號Y
     * @param pixelY
     *            the pixel Y coordinate that should be converted.
     * @param zoom
     *            the zoom level at which the coordinate should be converted.
     * @return the tile Y number.
    */
    pixelYToTileY(pixelY, zoom) {
        return Math.floor(Math.min(Math.max(pixelY / this.TILE_SIZE, 0), Math.pow(2, zoom) - 1));
    },
}