Method getResolutionFromScale

src/openlayers/mapping/WebMap.js:1970–1981

* @private * @function WebMap.prototype.getResolutionFromScale * @description 获取一个WMTS source需要的tileGrid * @param {number} scale - 比例尺（比例尺分母） * @param {number} dpi - 地图dpi * @param {string} unit - 单位 * @param {number} datumAxis * @returns {{res: Array, matrixIds: Array}}

(scale, dpi = dpiConfig.default, unit, datumAxis)

   * @returns {{res: Array, matrixIds: Array}}
   */
  getResolutionFromScale(scale, dpi = dpiConfig.default, unit, datumAxis) {
    //radio = 10000;
    let res;
    scale = +scale;
    scale = scale > 1.0 ? 1.0 / scale : scale;
    if (unit === 'degrees' || unit === 'dd' || unit === 'degree') {
      res = (0.0254 * 10000) / dpi / scale / ((Math.PI * 2 * datumAxis) / 360) / 10000;
    } else {
      res = (0.0254 * 10000) / dpi / scale / 10000;
    }
    return res;
  }

  /**
   * @private