基于高德地图的描点操作，监听地图缩放，展示合理数量的marker

1.根据两点经纬度算两点之间的距离函数

function Rad(d){ return d * Math.PI / 180.0;//经纬度转换成三角函数中度分表形式。 } //计算距离，参数分别为第一点的纬度，经度；第二点的纬度，经度 function GetDistance(lat1,lng1,lat2,lng2){

var radLat1 = Rad(lat1);
var radLat2 = Rad(lat2);
var a = radLat1 - radLat2;
var  b = Rad(lng1) - Rad(lng2);
var s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a/2),2) +
Math.cos(radLat1)*Math.cos(radLat2)*Math.pow(Math.sin(b/2),2)));
s = s *6378.137 ;// EARTH_RADIUS;
s = Math.round(s * 10000) / 10000; //输出为公里
//s=s.toFixed(4);
return s;

}

2.给地图绑定监听事件 map.on("zoomchange",function(){ for (var i = pathContentArr.length - 1; i >= 0; i--) { pathContentArr[i].setMap(null); } for (var i = pathMarkerArr.length - 1; i >= 0; i--) { pathMarkerArr[i].setMap(null); } pathMarkerArr=[]; pathContentArr=[]; drawMarkerByDistance(map.getZoom())

    })  

3.drawMarkerByDistance函数【会根据第i个点和第i+1个点之间的距离进行初步筛选，其中select函数对初步筛选出来的点进行了所有点两两之间距离的二次筛选】

function drawMarkerByDistance(zoom){ var perDistance=0; //当前累计公里数 var zoom=zoom||6; switch (zoom){ case 3: var targetDistance=800; //km break; case 4: var targetDistance=400; //km break; case 5: var targetDistance=200; //km break; case 6: var targetDistance=120; //km break; case 7: var targetDistance=60; //km break; case 8: var targetDistance=30; //km break; case 9: var targetDistance=15; //km break; case 10: var targetDistance=7; //km break; case 11: var targetDistance=4; //km break; case 12: var targetDistance=1; //km break; case 13: var targetDistance=0.5; //km break; default: var targetDistance=0.25; //km } var prepareToShowMarker=[]; for (var i = 0; i < curShipPolyLineData.length; i++) { //第一个点和最后一个点默认展示出来,累计长度大于目标长度的画出来 if (i==0||i==curShipPolyLineData.length-1 || (curShipPolyLineData[i].distance+perDistance)>targetDistance) { var marker={ lat:parseFloat(curShipPolyLineData[i].latitude), lng:parseFloat(curShipPolyLineData[i].longitude), course:curShipPolyLineData[i].course, AddTime: curShipPolyLineData[i].AddTime, } prepareToShowMarker.push(marker); } if(i<curShipPolyLineData.length-1 && i>1){ if ((curShipPolyLineData[i].distance+perDistance)>targetDistance) { perDistance=0; }else{ perDistance+=curShipPolyLineData[i].distance; } } }

    var select=function(arr){
        var flag=true;
        for(var i=0;i<arr.length;i++){
            for(var j=i+1;j<arr.length;j++){
                var curdistance=GetDistance(arr[i].lat,arr[i].lng,arr[j].lat,arr[j].lng);
                //如果还有靠得很近的点
                if (curdistance<targetDistance) {
                    flag=false;
                    //随机剔除掉一个i和j之间的一个点
                    Math.random()>0.5?arr.splice(i,1):arr.splice(j,1);
                    break;
                }
            }
            if(flag==false){
                break;
            }
        }
        //当数组中所有的点两两之间的距离都大于targetDistance的时候退出递归
        if (flag==false) {
            select(arr);
        }
    }
    select(prepareToShowMarker);
    for (var i = prepareToShowMarker.length - 1; i >= 0; i--) {
        var position=[prepareToShowMarker[i].lng,prepareToShowMarker[i].lat];
        var content = new AMap.Marker({
            content:prepareToShowMarker[i].AddTime,
            position: position,
            title: prepareToShowMarker[i].AddTime,
            offset:new AMap.Pixel(20,0),
            map: map
        });
        pathContentArr.push(content);
        var marker = new AMap.Marker({
            offset:new AMap.Pixel(0,0),
            icon:"new_images/arrow_r.png",
            angle:((prepareToShowMarker[i].course-90)%360),
            position: position,
            map: map
        });
        pathMarkerArr.push(marker);
    }


    
}