Google maps api 3 将多段线捕捉到道路

因此，我尝试使用步行移动模式将多段线捕捉到道路上，目前我有一条工作多段线，当用户的地理位置移动时会更新，然后从旧位置删除旧的多段线，并从新原点到目标绘制一条新的多段线，但这是一条直线，就像乌鸦飞线一样

function polyLine(myPos){

    var start;
    if (!start){
        start = geoMarker.position;
    }else{
        start = myPos;
    }
    var end = marker.position;

    var pathCoords = [start, end];
    var pathGo = new google.maps.Polyline({
        path: pathCoords,
        map: googleMap,
        strokeColor: "#FF0000",
        strokeOpacity: 0.7,
        strokeWeight: 2
    });
    polyLineArray.push(pathGo);
}

我还尝试了通过其他线程找到的各种代码片段，但都没有成功。这就是我目前正在玩的东西

function calcDist(myPos) {
var start;
if (!start){
    start = geoMarker.position;
}else{
    start = myPos;
}
var end = marker.position;

    var request = {
    origin: start,
    destination: end,
    travelMode: google.maps.TravelMode.WALKING
    };


directionsService.route(request, function(response, status) {
    if (status == google.maps.DirectionsStatus.OK)
    {

        var steps = response.routes[0].legs[0].steps;

        for(var step = 0; step < steps.length; step++)
        {
            polylineOptions = {
                    map: googleMap,
                    strokeColor: "#FF0000",
                    strokeOpacity: 0.7,
                    strokeWeight: 2,
                    path: steps[step].path
            }
        drawPoly = new google.maps.Polyline(polylineOptions);
        }

        drawPoly.getPath().push(ble);

    }

});
}

---

身份的价值是什么？

var directionsDisplay;
var directionsService = new google.maps.DirectionsService();

function calcDist(myPos) {
var start;
if (!start){
    start = geoMarker.position;
}else{
    start = myPos;
}
var end = marker.position;

    var request = {
        origin:start,
        destination:end,
        travelMode: google.maps.DirectionsTravelMode.WALKING
    };


directionsService.route(request, function(response, status) {
      if (status == google.maps.DirectionsStatus.OK) {
        directionsDisplay.setDirections(response);
      }
    });
}