矢量瓦片相关计算函数

摘要：根据该瓦片和计算出的行列号，即可取得鼠标点击位置的像素值。指定级别纬度对应的像素行号像素坐标转瓦片行列号像素坐标转瓦片行列号

import turf from "turf"
export default {
  TILE_SIZE: 256,
  /*
  * 获取指定级别的瓦片数目
  */
  _getMapSize(level) {
    return Math.pow(2, level);
  },
  /**
     * Convert a longitude coordinate (in degrees) to the tile X number at a
     * certain zoom level.经度转瓦片列号
     * @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.纬度转瓦片行号
      * @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.经纬度坐标(纬度)转屏幕像素坐标(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.经纬度坐标(经度)转屏幕像素坐标(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);
    },
   /*
   * 指定级别下，将宏观上的经度转换为对应列上的瓦片的像素矩阵列号(微观)
     例如：鼠标点击地图，鼠标位置在点击的瓦片内的行列号(即使像素行列号)。根据该瓦片(png)和计算出的行列号，即可取得鼠标点击位置的像素值。
  */
  _lngToPixelX(longitude, level) {
    let x = (longitude + 180) / 360;
    let pixelX = Math.floor(x * this._getMapSize(level) * 256 % 256);
    return pixelX;
  },
  /*
  * 指定级别纬度对应的像素行号
  */
  _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.
     * 像素坐标X转瓦片行列号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.
     * 像素坐标Y转瓦片行列号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));
    },
}