openlayers4加载百度地图、百度影像图、谷歌地图、谷歌影像图

// 自定义分辨率和瓦片坐标系
    var resolutions = [];
    var maxZoom = 18;
    // 计算百度使用的分辨率
    for (var i = 0; i <= maxZoom + 1; i++) {
        resolutions[i] = Math.pow(2, maxZoom - i);
    }
    var tilegrid = new ol.tilegrid.TileGrid({
        origin: [0, 0], // 设置原点坐标
        resolutions: resolutions // 设置分辨率
    });
    // 创建百度行政区划
    var baiduSource = new ol.source.TileImage({
        tileGrid: tilegrid,
        tileUrlFunction: function(tileCoord, pixelRatio, proj) {
            var z = tileCoord[0];
            var x = tileCoord[1];
            var y = tileCoord[2];

            // 百度瓦片服务url将负数使用M前缀来标识
            if (x < 0) {
                x = 'M' + (-x);
            }
            if (y < 0) {
                y = 'M' + (-y);
            }

            // return "http://online0.map.bdimg.com/onlinelabel/?qt=tile&x=" + x + "&y=" + y + "&z=" + z + "&styles=pl&udt=20170115&scaler=1&p=1";
            //street
            return 'http://online' + parseInt(Math.random() * 10) + '.map.bdimg.com/onlinelabel/?qt=tile&x=' +
                x + '&y=' + y + '&z=' + z + '&styles=pl&udt=20170620&scaler=1&p=1';
        }
    });
    // 百度影像
    var baiduSourceRaster= new ol.source.TileImage({
        tileGrid: tilegrid,
        tileUrlFunction: function(tileCoord, pixelRatio, proj) {
            var z = tileCoord[0];
            var x = tileCoord[1];
            var y = tileCoord[2];

            // 百度瓦片服务url将负数使用M前缀来标识
            if (x < 0) {
                x = 'M' + (-x);
            }
            if (y < 0) {
                y = 'M' + (-y);
            }
           return 'http://shangetu' + parseInt(Math.random() * 10) + '.map.bdimg.com/it/u=x=' + x +
                ';y=' + y + ';z=' + z + ';v=009;type=sate&fm=46&udt=20170606';
        }
    });
    // 百度标注
    var baiduSourceLabel = new ol.source.TileImage({
        tileGrid: tilegrid,
        tileUrlFunction: function(tileCoord, pixelRatio, proj) {
            var z = tileCoord[0];
            var x = tileCoord[1];
            var y = tileCoord[2];

            // 百度瓦片服务url将负数使用M前缀来标识
            if (x < 0) {
                x = 'M' + (-x);
            }
            if (y < 0) {
                y = 'M' + (-y);
            }
            return 'http://online' + parseInt(Math.random() * 10) + '.map.bdimg.com/onlinelabel/?qt=tile&x=' +
                x + '&y=' + y + '&z=' + z + '&styles=sl&udt=20170620&scaler=1&p=1';
        }
    });
    // 百度行政区划
    var baiduMapLayer = new ol.layer.Tile({
        source: baiduSource
    });

    // 百度地图标注
    var baiduMapLayerLabel = new ol.layer.Tile({
        source: baiduSourceLabel
    });
    //百度地图影像
    var baiduRasterLayer = new ol.layer.Tile({
        source: baiduSourceRaster
    });
    //谷歌行政区划
    var googleMapLayer = new ol.layer.Tile({
        source: new ol.source.XYZ({
            url: 'http://www.google.cn/maps/vt/pb=!1m4!1m3!1i{z}!2i{x}!3i{y}!2m3!1e0!2sm!3i345013117!3m8!2szh-CN!3scn!5e1105!12m4!1e68!2m2!1sset!2sRoadmap!4e0'
        })
    });
    //谷歌影像
    var googleRasterLayer = new ol.layer.Tile({
        source: new ol.source.TileImage({ url: 'http://mt2.google.cn/vt/lyrs=y&hl=zh-CN&gl=CN&src=app&x={x}&y={y}&z={z}&s=G' }),
        visible: false
    });