摘要：根據該瓦片和計算出的行列號，即可取得鼠標點擊位置的像素值。指定級別緯度對應的像素行號像素坐標轉瓦片行列號像素坐標轉瓦片行列號

import turf from "turf"
export default {
  TILE_SIZE: 256,
  /*
  * 獲取指定級別的瓦片數目
  */
  _getMapSize(level) {
    return Math.pow(2, level);
  },
  /**
     * Convert a longitude coordinate (in degrees) to the tile X number at a
     * certain zoom level.經度轉瓦片列號
     * @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.經緯度坐標(緯度)轉屏幕像素坐標(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.經緯度坐標(經度)轉屏幕像素坐標(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，將宏觀上的經度轉換為對應列上的瓦片的像素矩陣列號(微觀)
     例如：鼠標點擊地圖，鼠標位置在點擊的瓦片內的行列號(即使像素行列號)。根據該瓦片(png)和計算出的行列號，即可取得鼠標點擊位置的像素值。
  */
  _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X轉瓦片行列號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Y轉瓦片行列號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));
    },
}