Openlayers4动态绘制地图分幅网络

在Openlayers地图上根据地图分幅规则，绘制分幅网格，需要注意的有几点：

1确认什么比例尺时展示什么1:100万、1:50万...比例尺的分幅

2根据地图当前视窗位置，动态绘制注记和网络，因为全部绘制的话，网格和注意太多，严重影像运行速度

3绘制经线和纬线，不绘制网格，网格严重内存更多

代码如下：

 addSheetNumber(number){
      getLayerByName(this.$map2d, "drawLayer")
            .getSource()
            .clear();
            var d1=6;
            var d2=4;
      switch (number) {
        case 1000000:
             d1=6;
             d2=4;
          break;
        case 500000:
             d1=3;
             d2=2;          
          break;
        case 250000:
             d1=1.5;
             d2=1;            
          break;
        case 100000:
             d1=0.5;
             d2=0.3333;            
          break;    
        default:
          break;
      }  
      for (let index = 0; index < 88/d2+1; index++) {
         if(index==0){this.outLine(index*d2,-180,index*d2,180)}else{
         this.outLine(index*d2,-180,index*d2,180);
         this.outLine(-index*d2,-180,-index*d2,180);
         }
        }
         //画经线
        for (let i = 0; i < 360/d1; i++) {
          this.outLine(-88,-180+i*d1,88,-180+i*d1);     
        }    
    },
    toggleSheetNumber(){
      const that=this;
      var view=this.$map2d.getView();
      if(this.sheetType!=0){
      //第二次点击清除网络  
      view.un('change:resolution',that.changeListener);
      view.un('change',that.resetNumberText);
      getLayerByName(this.$map2d, "drawLayer")
            .getSource()
            .clear();
      getLayerByName(this.$map2d, "textLayer").getSource()
            .clear();
      this.sheetType=0;
            return;
      }
      view.on('change:resolution',that.changeListener);
      view.on('change',that.resetNumberText);
      this.changeListener();
    },
    changeListener(e){
        var view=this.$map2d.getView();
        var ruler=view.getResolution(); 
        if(ruler>0.02197&&this.sheetType!=1000000){
        this.sheetType=1000000;
        this.addSheetNumber(1000000);
        }
        else if(ruler<0.02197&&ruler>0.00549&&this.sheetType!=500000){
        this.sheetType=500000;
        this.addSheetNumber(500000);
        }else if(ruler<0.00549&&ruler>0.00297&&this.sheetType!=250000){
        this.sheetType=250000;
        this.addSheetNumber(250000);
        }else if(ruler<0.00297&&this.sheetType!=100000){
        this.sheetType=100000;
        this.addSheetNumber(100000);
        }  
    },
    resetNumberText(e){
      getLayerByName(this.$map2d, "textLayer").getSource()
            .clear();
      let view=e.target;
      var extent=view.calculateExtent();

      if(extent[0]<-180){extent[0]=-180}
      if(extent[1]<-88){extent[1]=-88}
      if(extent[2]>180){extent[2]=180}
      if(extent[3]>88){extent[3]=88}
      let ruler=view.getResolution(); 
      var d1=6;
      var d2=4;
      switch (this.sheetType) {
        case 1000000:
             d1=6;
             d2=4;
          break;
        case 500000:
             d1=3;
             d2=2;          
          break;
        case 250000:
             d1=1.5;
             d2=1;            
          break;
        case 100000:
             d1=0.5;
             d2=0.3333;            
          break;    
        default:
          break;
      }

      var i1=Math.floor((extent[0]+180)/d1);
      if((extent[0]-i1*d1-d1/2)>0){i1++}
      var i2=Math.floor((extent[2]+180)/d1);
      if((extent[2]-i2*d1-d1/2)>0){i2++}
      var j1=Math.floor((extent[1]+88)/d2);
      if((extent[1]-j1*d2-d2/2)>0){j1++}
      var j2=Math.floor((extent[3]+88)/d2);
      if((extent[3]-j2*d2-d2/2)>0){j2++} 
      for (let index = i1; index < i2; index++) {
        this.outLabel(index*d1-180+d1/2,extent[3],String(index+1))
      }
      for (let h = j1; h < j2; h++) {
        var text=h;
        if(h<88/d2){
          text="S"+Math.round(88/d2-h)
        }
        else{text="N"+Math.round(h-88/d2+1)}
        this.outLabel(extent[0],h*d2-88+d2/2,text)
      }
    },

 outLabel(lon,lat,text){
      var geom = new ol.geom.Point([lon, lat]);
      var feature = new ol.Feature({
        geometry: geom,
        labelPoint: geom,
        name: text
      });
      feature.setStyle(this.createLabelStyle(feature));
      var vectorLayer = getLayerByName(this.$map2d, "textLayer");
      var vectorSource = vectorLayer.getSource();
      vectorSource.addFeature(feature);
    },
    //生成样式
    createLineStyle(feature) {
      return new ol.style.Style({
        stroke: new ol.style.Stroke({
          color: "red", //边框颜色
          width: 2 // 边框宽度
        })
      });
    },
    createLabelStyle(feature) {
      return new ol.style.Style({
        text: new ol.style.Text({
          textAlign: "center",
          textBaseLine: "start",
          offsetX:10,
          offsetY:5,
          font: "bold 10px 微软雅黑",
          text: feature.get("name"),
          fill: new ol.style.Fill({
            color: "red"
          })
        })
      });
    },

最后结果如下图所示：

缺点：无法在每一个网格里添加文字