How to implement map grid using Baidu Maps

var ZMap = function (id, center, level) {
 this.initCenter = new ZPoint(116.404, 39.915);//初始化的中心点，同时为了定义网格的中心点
 this.id = id;//p的id
 this.level = level ? level : 13;//地图级别
 this.center = center ? center : this.initCenter;//中心点
 this.map = null;//百度地图实例
 this.xgrids = [];//经线
 this.ygrids = [];//纬线
 this.beSelectBounds = {};
 this.bounds = null;//当前地图的四个顶点
 this.span = null;//当前网格的跨度
 this.init();
}
ZMap.prototype = {
 init: function () {//全局初始化
  var zMap = this;
  this.map = new BMap.Map(this.id);
  this.map.centerAndZoom(this.center.point, this.level);
  this.map.enableScrollWheelZoom();
  this.map.disableInertialDragging();
  this.map.addControl(new BMap.NavigationControl({
   anchor: BMAP_ANCHOR_BOTTOM_RIGHT,
   type: BMAP_NAVIGATION_CONTROL_ZOOM
  })); //缩放按钮
  this.map.addControl(new BMap.ScaleControl({anchor: BMAP_ANCHOR_BOTTOM_LEFT, offset: new BMap.Size(80, 25)})); //比例尺
  this.map.disableDoubleClickZoom();
  this.map.setMapStyle({style: 'googlelite'});
  this.initProperty();
  this.initGrid();
  //添加移动后的点击事件
  this.map.addEventListener("dragend", function () {
   zMap.initProperty();
   zMap.initGrid();
  });
  //添加放大或缩小时的事件
  this.map.addEventListener("zoomend", function () {
   zMap.initProperty();
   zMap.initGrid();
  });
  //设置点击事件
  this.map.addEventListener("click", function (e) {
   var point = e.point;
   //获取当前点是在哪个区块内,获取正方形的四个顶点
   var points = zMap.getGrid(point);
   //判断当前区域是否已经被选中过，如果被选中过则取消选中
   var key = '' + points[0].lng + points[0].lat + points[2].lng + points[2].lat;//使用两个点的坐标作为key
   if (zMap.beSelectBounds[key]) {
    zMap.map.removeOverlay(zMap.beSelectBounds[key]);
    delete zMap.beSelectBounds[key];
    return;
   }
   var polygon = new BMap.Polygon(points, {strokeColor: "red", strokeWeight: 2, strokeOpacity: 0.5});
   zMap.map.addOverlay(polygon);
   zMap.beSelectBounds[key] = polygon;
  });
 },
 initProperty: function () {//初始化当前地图的状态
  this.level = this.map.getZoom();
  this.bounds = {
   x1: this.map.getBounds().getSouthWest().lng,
   y1: this.map.getBounds().getSouthWest().lat,
   x2: this.map.getBounds().getNorthEast().lng,
   y2: this.map.getBounds().getNorthEast().lat
  };
  this.span = this.getSpan();//需要使用level属性
 },
 initGrid: function () {//初始化网格
  var zMap = this;
  //将原来的网格线先去掉
  for (var i in zMap.xgrids) {
   this.map.removeOverlay(zMap.xgrids[i]);
  }
  zMap.xgrids = [];
  for (var i in zMap.ygrids) {
   this.map.removeOverlay(zMap.ygrids[i]);
  }
  zMap.ygrids = [];
  //获取当前网格跨度
  var span = zMap.span;
  //初始化地图上的网格
  for (var i = zMap.bounds.x1 + (zMap.initCenter.point.lng - zMap.bounds.x1) % span.x - span.x; i < zMap.bounds.x2 + span.x; i += span.x) {
   var polyline = new BMap.Polyline([
    new BMap.Point(i.toFixed(6), zMap.bounds.y1),
    new BMap.Point(i.toFixed(6), zMap.bounds.y2)
   ], {strokeColor: "black", strokeWeight: 1, strokeOpacity: 0.5});
   zMap.xgrids.push(polyline);
   zMap.map.addOverlay(polyline);
  }
  for (var i = zMap.bounds.y1 + (zMap.initCenter.point.lat - zMap.bounds.y1) % span.y - span.y; i < zMap.bounds.y2 + span.y; i += span.y) {
   var polyline = new BMap.Polyline([
    new BMap.Point(zMap.bounds.x1, i.toFixed(6)),
    new BMap.Point(zMap.bounds.x2, i.toFixed(6))
   ], {strokeColor: "black", strokeWeight: 1, strokeOpacity: 0.5});
   zMap.ygrids.push(polyline);
   zMap.map.addOverlay(polyline);
  }
 },
 getSpan: function () {//获取网格的跨度
  var scale = 0.75;
  var x = 0.00064;
  for (var i = this.level; i < 19; i++) {
   x *= 2;
  }
  var y = parseFloat((scale * x).toFixed(5));
  return {x: x, y: y};
 },
 getGrid: function (point) {//返回当前点在所在区块的四个顶点
  var zMap = this;
  //先找出两条纵线坐标
  var xpoints = this.xgrids.map(function (polyline) {
   return polyline.getPath()[0].lng;
  }).filter(function (lng) {
   return Math.abs(lng - point.lng) <= zMap.span.x;
  }).sort(function (a, b) {
   return a - b;
  }).slice(0, 2);
  //再找出两条横线的坐标
  var ypoints = this.ygrids.map(function (polyline) {
   return polyline.getPath()[0].lat;
  }).filter(function (lat) {
   return Math.abs(lat - point.lat) <= zMap.span.y;
  }).sort(function (a, b) {
   return a - b;
  }).slice(0, 2);
  return [
   new BMap.Point(xpoints[0], ypoints[0]),
   new BMap.Point(xpoints[0], ypoints[1]),
   new BMap.Point(xpoints[1], ypoints[1]),
   new BMap.Point(xpoints[1], ypoints[0])
  ];
 },
 reset: function () {//重置
  this.map.reset();
 }
}
var ZPoint = function (x, y, code) {
 this.code = code;
 this.point = new BMap.Point(x, y);
}