地图区域大数据量 marker 坐标点高效抽稀算法

//抽稀
if (mapZoom >= 15 && mapZoom <= 16) {
    currentMarkerMap = new HashMap();

    var getKey = function (lng, lat, len, ratio) { //如果计算结果数量较少，就调大ratio
        var a = (10000 + lng * ratio).toString().substr(0, len);
        var b = (10000 + lat * ratio).toString().substr(0, len)
        return a + "," + b;
    };

    for (var i = 0; i < forAdd.length; i++) {
        var marker = forAdd[i];

        var key;
        if (mapZoom == 15) key = getKey(marker.geometry.x, marker.geometry.y, 9, 1);
        if (mapZoom == 16) key = getKey(marker.geometry.x, marker.geometry.y, 10, 1);

        if (!currentMarkerMap.containsKey(key)) {
            currentMarkerMap.put(key, marker);
        }
    }
}

var forClear = [];
var currentMarkerMap = new HashMap();