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));

},

}

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