原文出处:
https://blog.csdn.net/u010366748/article/details/50097865 (更详细的解说)
var bounds = map.getBounds(); //获取地图可视区域
var sw = bounds.getSouthWest(); //获取西南角的经纬度(左下端点)
var ne = bounds.getNorthEast(); //获取东北角的经纬度(右上端点)
var wn = new BMap.Point(sw.lng, ne.lat); //获取西北角的经纬度(左上端点)
var es = new BMap.Point(ne.lng, sw.lat); //获取东南角的经纬度(右下端点)