ol/proj/epsg3857.js

OpenLayers mapping library

/**
 * @module ol/proj/epsg3857
 */
import Projection from './Projection.js';

/**
 * Radius of WGS84 sphere
 *
 * @const
 * @type {number}
 */
export const RADIUS = 6378137;

/**
 * @const
 * @type {number}
 */
export const HALF_SIZE = Math.PI * RADIUS;

/**
 * @const
 * @type {import("../extent.js").Extent}
 */
export const EXTENT = [-HALF_SIZE, -HALF_SIZE, HALF_SIZE, HALF_SIZE];

/**
 * @const
 * @type {import("../extent.js").Extent}
 */
export const WORLD_EXTENT = [-180, -85, 180, 85];

/**
 * Maximum safe value in y direction
 * @const
 * @type {number}
 */
export const MAX_SAFE_Y = RADIUS * Math.log(Math.tan(Math.PI / 2));

/**
 * @classdesc
 * Projection object for web/spherical Mercator (EPSG:3857).
 */
class EPSG3857Projection extends Projection {
  /**
   * @param {string} code Code.
   */
  constructor(code) {
    super({
      code: code,
      units: 'm',
      extent: EXTENT,
      global: true,
      worldExtent: WORLD_EXTENT,
      getPointResolution: function (resolution, point) {
        return resolution / Math.cosh(point[1] / RADIUS);
      },
    });
  }
}

/**
 * Projections equal to EPSG:3857.
 *
 * @const
 * @type {Array<import("./Projection.js").default>}
 */
export const PROJECTIONS = [
  new EPSG3857Projection('EPSG:3857'),
  new EPSG3857Projection('EPSG:102100'),
  new EPSG3857Projection('EPSG:102113'),
  new EPSG3857Projection('EPSG:900913'),
  new EPSG3857Projection('http://www.opengis.net/def/crs/EPSG/0/3857'),
  new EPSG3857Projection('http://www.opengis.net/gml/srs/epsg.xml#3857'),
];

/**
 * Transformation from EPSG:4326 to EPSG:3857.
 *
 * @param {Array<number>} input Input array of coordinate values.
 * @param {Array<number>} [output] Output array of coordinate values.
 * @param {number} [dimension] Dimension (default is `2`).
 * @param {number} [stride] Stride (default is `dimension`).
 * @return {Array<number>} Output array of coordinate values.
 */
export function fromEPSG4326(input, output, dimension, stride) {
  const length = input.length;
  dimension = dimension > 1 ? dimension : 2;
  stride = stride ?? dimension;
  if (output === undefined) {
    if (dimension > 2) {
      // preserve values beyond second dimension
      output = input.slice();
    } else {
      output = new Array(length);
    }
  }
  for (let i = 0; i < length; i += stride) {
    output[i] = (HALF_SIZE * input[i]) / 180;
    let y = RADIUS * Math.log(Math.tan((Math.PI * (+input[i + 1] + 90)) / 360));
    if (y > MAX_SAFE_Y) {
      y = MAX_SAFE_Y;
    } else if (y < -MAX_SAFE_Y) {
      y = -MAX_SAFE_Y;
    }
    output[i + 1] = y;
  }
  return output;
}

/**
 * Transformation from EPSG:3857 to EPSG:4326.
 *
 * @param {Array<number>} input Input array of coordinate values.
 * @param {Array<number>} [output] Output array of coordinate values.
 * @param {number} [dimension] Dimension (default is `2`).
 * @param {number} [stride] Stride (default is `dimension`).
 * @return {Array<number>} Output array of coordinate values.
 */
export function toEPSG4326(input, output, dimension, stride) {
  const length = input.length;
  dimension = dimension > 1 ? dimension : 2;
  stride = stride ?? dimension;
  if (output === undefined) {
    if (dimension > 2) {
      // preserve values beyond second dimension
      output = input.slice();
    } else {
      output = new Array(length);
    }
  }
  for (let i = 0; i < length; i += stride) {
    output[i] = (180 * input[i]) / HALF_SIZE;
    output[i + 1] =
      (360 * Math.atan(Math.exp(input[i + 1] / RADIUS))) / Math.PI - 90;
  }
  return output;
}