createOpenStreetMapImageryProvider.js

define([
        '../Core/Credit',
        '../Core/defaultValue',
        '../Core/DeveloperError',
        '../Core/Rectangle',
        '../Core/WebMercatorTilingScheme',
        './UrlTemplateImageryProvider'
    ], function(
        Credit,
        defaultValue,
        DeveloperError,
        Rectangle,
        WebMercatorTilingScheme,
        UrlTemplateImageryProvider) {
    'use strict';

    var trailingSlashRegex = /\/$/;
    var defaultCredit = new Credit('MapQuest, Open Street Map and contributors, CC-BY-SA');

    /**
     * Creates a {@link UrlTemplateImageryProvider} instance that provides tiled imagery hosted by OpenStreetMap
     * or another provider of Slippy tiles.  The default url connects to OpenStreetMap's volunteer-run
     * servers, so you must conform to their
     * {@link http://wiki.openstreetmap.org/wiki/Tile_usage_policy|Tile Usage Policy}.
     *
     * @exports createOpenStreetMapImageryProvider
     *
     * @param {Object} [options] Object with the following properties:
     * @param {String} [options.url='https://a.tile.openstreetmap.org'] The OpenStreetMap server url.
     * @param {String} [options.fileExtension='png'] The file extension for images on the server.
     * @param {Object} [options.proxy] A proxy to use for requests. This object is expected to have a getURL function which returns the proxied URL.
     * @param {Rectangle} [options.rectangle=Rectangle.MAX_VALUE] The rectangle of the layer.
     * @param {Number} [options.minimumLevel=0] The minimum level-of-detail supported by the imagery provider.
     * @param {Number} [options.maximumLevel] The maximum level-of-detail supported by the imagery provider, or undefined if there is no limit.
     * @param {Ellipsoid} [options.ellipsoid] The ellipsoid.  If not specified, the WGS84 ellipsoid is used.
     * @param {Credit|String} [options.credit='MapQuest, Open Street Map and contributors, CC-BY-SA'] A credit for the data source, which is displayed on the canvas.
     * @returns {UrlTemplateImageryProvider} The imagery provider.
     *
     * @exception {DeveloperError} The rectangle and minimumLevel indicate that there are more than four tiles at the minimum level. Imagery providers with more than four tiles at the minimum level are not supported.
     *
     * @see ArcGisMapServerImageryProvider
     * @see BingMapsImageryProvider
     * @see GoogleEarthEnterpriseMapsProvider
     * @see SingleTileImageryProvider
     * @see createTileMapServiceImageryProvider
     * @see WebMapServiceImageryProvider
     * @see WebMapTileServiceImageryProvider
     * @see UrlTemplateImageryProvider
     *
     *
     * @example
     * var osm = Cesium.createOpenStreetMapImageryProvider({
     *     url : 'https://a.tile.openstreetmap.org/'
     * });
     *
     * @see {@link http://wiki.openstreetmap.org/wiki/Main_Page|OpenStreetMap Wiki}
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     */
    function createOpenStreetMapImageryProvider(options) {
        options = defaultValue(options, {});

        var url = defaultValue(options.url, 'https://a.tile.openstreetmap.org/');

        if (!trailingSlashRegex.test(url)) {
            url = url + '/';
        }

        var fileExtension = defaultValue(options.fileExtension, 'png');

        var tilingScheme = new WebMercatorTilingScheme({ ellipsoid : options.ellipsoid });

        var tileWidth = 256;
        var tileHeight = 256;

        var minimumLevel = defaultValue(options.minimumLevel, 0);
        var maximumLevel = options.maximumLevel;

        var rectangle = defaultValue(options.rectangle, tilingScheme.rectangle);

        // Check the number of tiles at the minimum level.  If it's more than four,
        // throw an exception, because starting at the higher minimum
        // level will cause too many tiles to be downloaded and rendered.
        var swTile = tilingScheme.positionToTileXY(Rectangle.southwest(rectangle), minimumLevel);
        var neTile = tilingScheme.positionToTileXY(Rectangle.northeast(rectangle), minimumLevel);
        var tileCount = (Math.abs(neTile.x - swTile.x) + 1) * (Math.abs(neTile.y - swTile.y) + 1);
        //>>includeStart('debug', pragmas.debug);
        if (tileCount > 4) {
            throw new DeveloperError('The rectangle and minimumLevel indicate that there are ' + tileCount + ' tiles at the minimum level. Imagery providers with more than four tiles at the minimum level are not supported.');
        }
        //>>includeEnd('debug');

        var credit = defaultValue(options.credit, defaultCredit);
        if (typeof credit === 'string') {
            credit = new Credit(credit);
        }

        var templateUrl = url + '{z}/{x}/{y}.' + fileExtension;

        return new UrlTemplateImageryProvider({
            url: templateUrl,
            proxy: options.proxy,
            credit: credit,
            tilingScheme: tilingScheme,
            tileWidth: tileWidth,
            tileHeight: tileHeight,
            minimumLevel: minimumLevel,
            maximumLevel: maximumLevel,
            rectangle: rectangle
        });
    }

    return createOpenStreetMapImageryProvider;
});