如何根据沿线距离在谷歌地图折线上添加标记？

Question

我正在尝试创建一个谷歌地图，用户可以在其中绘制他步行/跑步/骑自行车的路线，并查看他跑了多长时间。带有 getLength() 方法的 GPolyline 类在这方面非常有帮助（至少对于 Google Maps API V2），但我想根据距离添加标记，例如例如 1 公里、5 公里、10 公里等的标记，但似乎没有明显的方法可以根据折线上的距离来查找折线上的点。有什么建议吗？

Answer 1

回答了类似的问题几个月前，关于如何在 SQL Server 2008 的服务器端解决这个问题，我使用 Google 地图 API v2。

在本示例中，我们使用一条简单的 4 点折线，总长度约为 8,800 米。下面的代码片段将定义这条折线并将其渲染在地图上：

var map = new GMap2(document.getElementById('map_canvas'));

var points = [
   new GLatLng(47.656, -122.360),
   new GLatLng(47.656, -122.343),
   new GLatLng(47.690, -122.310),
   new GLatLng(47.690, -122.270)
];

var polyline = new GPolyline(points, '#f00', 6);

map.setCenter(new GLatLng(47.676, -122.343), 12);
map.addOverlay(polyline);

现在，在我们采用实际算法之前，我们需要一个函数，在给定起点、终点以及沿该点行驶的距离时返回目的地点幸运的是，Chris Veness 在 计算距离，有一些方便的 JavaScript 实现，纬度/经度点之间的方位角和更多信息。

特别是，我从上述来源改编了以下两种方法来与 Google 的 GLatLng 类一起使用：

• 给定距起点的距离和方位的目标点
• Bearing

这些用于通过方法 moveTowards() 扩展 Google 的 GLatLng 类，当给定另一个点和距离时，该方法以米为单位，当从原始点向作为参数传递的点行进的距离时，它将沿着该线返回另一个 GLatLng 。

GLatLng.prototype.moveTowards = function(point, distance) {   
   var lat1 = this.lat().toRad();
   var lon1 = this.lng().toRad();
   var lat2 = point.lat().toRad();
   var lon2 = point.lng().toRad();         
   var dLon = (point.lng() - this.lng()).toRad();

   // Find the bearing from this point to the next.
   var brng = Math.atan2(Math.sin(dLon) * Math.cos(lat2),
                         Math.cos(lat1) * Math.sin(lat2) -
                         Math.sin(lat1) * Math.cos(lat2) * 
                         Math.cos(dLon));

   var angDist = distance / 6371000;  // Earth's radius.

   // Calculate the destination point, given the source and bearing.
   lat2 = Math.asin(Math.sin(lat1) * Math.cos(angDist) + 
                    Math.cos(lat1) * Math.sin(angDist) * 
                    Math.cos(brng));

   lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(angDist) *
                            Math.cos(lat1), 
                            Math.cos(angDist) - Math.sin(lat1) *
                            Math.sin(lat2));

   if (isNaN(lat2) || isNaN(lon2)) return null;

   return new GLatLng(lat2.toDeg(), lon2.toDeg());
}

有了这个方法，我们现在可以按如下方式解决问题：

1. 迭代路径的每个点。
2. 求迭代中当前点到下一个点之间的距离。

3. 如果点 2 的距离大于我们需要在路径上行驶的距离：

   ...那么目标点就在这个点和下一个点之间。只需将 moveTowards() 方法应用于当前点，并传递下一个点和要行进的距离。返回结果并中断迭代。

   其他：

   ...目标点距离迭代中的下一个点更远。我们需要从沿着路径行驶的总距离中减去这一点和下一点之间的距离。继续使用修改后的距离进行迭代。

您可能已经注意到，我们可以轻松地递归实现上述内容，而不是迭代。那么让我们这样做：

function moveAlongPath(points, distance, index) {
   index = index || 0;  // Set index to 0 by default.

   if (index < points.length) {
      // There is still at least one point further from this point.

      // Construct a GPolyline to use its getLength() method.
      var polyline = new GPolyline([points[index], points[index + 1]]);

      // Get the distance from this point to the next point in the polyline.
      var distanceToNextPoint = polyline.getLength();

      if (distance <= distanceToNextPoint) {
         // distanceToNextPoint is within this point and the next. 
         // Return the destination point with moveTowards().
         return points[index].moveTowards(points[index + 1], distance);
      }
      else {
         // The destination is further from the next point. Subtract
         // distanceToNextPoint from distance and continue recursively.
         return moveAlongPath(points,
                              distance - distanceToNextPoint,
                              index + 1);
      }
   }
   else {
      // There are no further points. The distance exceeds the length  
      // of the full path. Return null.
      return null;
   }  
}

使用上面的方法，如果我们定义一个 GLatLng 点数组，并使用该点数组和一个距离调用 moveAlongPath() 函数2,500 米，它将在距离第一个点 2.5 公里的路径上返回 GLatLng。

var points = [
   new GLatLng(47.656, -122.360),
   new GLatLng(47.656, -122.343),
   new GLatLng(47.690, -122.310),
   new GLatLng(47.690, -122.270)
];

var destinationPointOnPath = moveAlongPath(points, 2500);

// destinationPointOnPath will be a GLatLng on the path 
// at 2.5km from the start.

因此，我们需要做的就是为路径上需要的每个检查点调用 moveAlongPath() 。如果您需要 1 公里、5 公里和 10 公里处的三个标记，您可以简单地执行以下操作：

map.addOverlay(new GMarker(moveAlongPath(points, 1000)));
map.addOverlay(new GMarker(moveAlongPath(points, 5000)));
map.addOverlay(new GMarker(moveAlongPath(points, 10000)));

但是请注意，如果我们请求距离总数更远的检查点，moveAlongPath() 可能会返回 null路径的长度，因此在将返回值传递给 new GMarker() 之前检查它是明智的做法。

我们可以将其整合在一起以进行全面实施。在此示例中，我们沿着前面定义的 8.8 公里路径每 1,000 米放置一个标记：

<!DOCTYPE html>
<html> 
<head> 
   <meta http-equiv="content-type" content="text/html; charset=UTF-8"/> 
   <title>Google Maps - Moving point along a path</title> 
   <script src="http://maps.google.com/maps?file=api&v=2&sensor=false"
           type="text/javascript"></script> 
</head> 
<body onunload="GUnload()"> 
   <div id="map_canvas" style="width: 500px; height: 300px;"></div>

   <script type="text/javascript"> 

   Number.prototype.toRad = function() {
      return this * Math.PI / 180;
   }

   Number.prototype.toDeg = function() {
      return this * 180 / Math.PI;
   }

   GLatLng.prototype.moveTowards = function(point, distance) {   
      var lat1 = this.lat().toRad();
      var lon1 = this.lng().toRad();
      var lat2 = point.lat().toRad();
      var lon2 = point.lng().toRad();         
      var dLon = (point.lng() - this.lng()).toRad();

      // Find the bearing from this point to the next.
      var brng = Math.atan2(Math.sin(dLon) * Math.cos(lat2),
                            Math.cos(lat1) * Math.sin(lat2) -
                            Math.sin(lat1) * Math.cos(lat2) * 
                            Math.cos(dLon));

      var angDist = distance / 6371000;  // Earth's radius.

      // Calculate the destination point, given the source and bearing.
      lat2 = Math.asin(Math.sin(lat1) * Math.cos(angDist) + 
                       Math.cos(lat1) * Math.sin(angDist) * 
                       Math.cos(brng));

      lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(angDist) *
                               Math.cos(lat1), 
                               Math.cos(angDist) - Math.sin(lat1) *
                               Math.sin(lat2));

      if (isNaN(lat2) || isNaN(lon2)) return null;

      return new GLatLng(lat2.toDeg(), lon2.toDeg());
   }

   function moveAlongPath(points, distance, index) {        
      index = index || 0;  // Set index to 0 by default.

      if (index < points.length) {
         // There is still at least one point further from this point.

         // Construct a GPolyline to use the getLength() method.
         var polyline = new GPolyline([points[index], points[index + 1]]);

         // Get the distance from this point to the next point in the polyline.
         var distanceToNextPoint = polyline.getLength();

         if (distance <= distanceToNextPoint) {
            // distanceToNextPoint is within this point and the next. 
            // Return the destination point with moveTowards().
            return points[index].moveTowards(points[index + 1], distance);
         }
         else {
            // The destination is further from the next point. Subtract
            // distanceToNextPoint from distance and continue recursively.
            return moveAlongPath(points,
                                 distance - distanceToNextPoint,
                                 index + 1);
         }
      }
      else {
         // There are no further points. The distance exceeds the length  
         // of the full path. Return null.
         return null;
      }  
   }

   var map = new GMap2(document.getElementById('map_canvas'));

   var points = [
      new GLatLng(47.656, -122.360),
      new GLatLng(47.656, -122.343),
      new GLatLng(47.690, -122.310),
      new GLatLng(47.690, -122.270)
   ];

   var polyline = new GPolyline(points, '#f00', 6);

   var nextMarkerAt = 0;     // Counter for the marker checkpoints.
   var nextPoint = null;     // The point where to place the next marker.

   map.setCenter(new GLatLng(47.676, -122.343), 12);

   // Draw the path on the map.
   map.addOverlay(polyline);

   // Draw the checkpoint markers every 1000 meters.
   while (true) {
      // Call moveAlongPath which will return the GLatLng with the next
      // marker on the path.
      nextPoint = moveAlongPath(points, nextMarkerAt);

      if (nextPoint) {
         // Draw the marker on the map.
         map.addOverlay(new GMarker(nextPoint));

         // Add +1000 meters for the next checkpoint.
         nextMarkerAt += 1000;    
      }
      else {
         // moveAlongPath returned null, so there are no more check points.
         break;
      }            
   }
   </script>
</body> 
</html>

上例的屏幕截图，显示每 1,000 米一个标记：

Answer 2

这些是所需函数的原型：

google.maps.Polygon.prototype.Distance = function() {
   var dist = 0;
   for (var i=1; i < this.getPath().getLength(); i++) {
      dist += this.getPath().getAt(i).distanceFrom(this.getPath().getAt(i-1));
   }
   return dist;
}

google.maps.LatLng.prototype.distanceFrom = function(newLatLng) {
    //var R = 6371; // km (change this constant to get miles)
    var R = 6378100; // meters
    var lat1 = this.lat();
    var lon1 = this.lng();
    var lat2 = newLatLng.lat();
    var lon2 = newLatLng.lng();
    var dLat = (lat2-lat1) * Math.PI / 180;
    var dLon = (lon2-lon1) * Math.PI / 180;
    var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
      Math.cos(lat1 * Math.PI / 180 ) * Math.cos(lat2 * Math.PI / 180 ) *
      Math.sin(dLon/2) * Math.sin(dLon/2);
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
    var d = R * c;
    return d;
}

源

Answer 3

最好的方法可能是计算这些点的位置。

作为基本算法，您可以迭代折线中的所有点，并计算累积距离 - 如果下一段使您超出距离，您可以在达到距离的点进行插值 - 然后只需添加一个兴趣点到你的地图上。

Answer 4

我已经使用 Martin Zeitler 方法来处理 Google Map V3，并且工作正常。

 function init() {
       var mapOptions = {
            zoom: 15,
            center: new google.maps.LatLng(-6.208437004433984, 106.84543132781982),
            suppressInfoWindows: true,
                     };

        // Get all html elements for map
        var mapElement = document.getElementById('map1');

        // Create the Google Map using elements
        map = new google.maps.Map(mapElement, mapOptions);

        var nextMarkerAt = 0;     // Counter for the marker checkpoints.
        var nextPoint = null;     // The point where to place the next marker.


        while (true) {

            var routePoints = [ new google.maps.LatLng(47.656, -122.360),
                                new google.maps.LatLng(47.656, -122.343),
                                new google.maps.LatLng(47.690, -122.310),
                                new google.maps.LatLng(47.690, -122.270)];

                nextPoint = moveAlongPath(routePoints, nextMarkerAt);

            if (nextPoint) {
              //Adding marker from localhost
                MarkerIcon = "http://192.168.1.1/star.png";
                var marker = new google.maps.Marker
                    ({position: nextPoint,
                        map: map,
                        icon: MarkerIcon
                    });
                // Add +1000 meters for the next checkpoint.
                nextMarkerAt +=1000;

            }
            else {
                // moveAlongPath returned null, so there are no more check points.
                break;
            }
        }
 }


   Number.prototype.toRad = function () {
        return this * Math.PI / 180;
    }

    Number.prototype.toDeg = function () {
        return this * 180 / Math.PI;
    }

    function moveAlongPath(point, distance, index) {
        index = index || 0;  // Set index to 0 by default.

        var routePoints = [];

        for (var i = 0; i < point.length; i++) {
            routePoints.push(point[i]);
        }

        if (index < routePoints.length) {
            // There is still at least one point further from this point.

            // Construct a GPolyline to use the getLength() method.
            var polyline = new google.maps.Polyline({
                path: [routePoints[index], routePoints[index + 1]],
                strokeColor: '#FF0000',
                strokeOpacity: 0.8,
                strokeWeight: 2,
                fillColor: '#FF0000',
                fillOpacity: 0.35
            });

            // Get the distance from this point to the next point in the polyline.
            var distanceToNextPoint = polyline.Distance();

            if (distance <= distanceToNextPoint) {
                // distanceToNextPoint is within this point and the next.
                // Return the destination point with moveTowards().
                return moveTowards(routePoints, distance,index);
            }
            else {
                // The destination is further from the next point. Subtract
                // distanceToNextPoint from distance and continue recursively.
                return moveAlongPath(routePoints,
                    distance - distanceToNextPoint,
                    index + 1);
            }
        }
        else {
            // There are no further points. The distance exceeds the length
            // of the full path. Return null.
            return null;
        }
    }

    function moveTowards(point, distance,index) {

        var lat1 = point[index].lat.toRad();
        var lon1 = point[index].lng.toRad();
        var lat2 = point[index+1].lat.toRad();
        var lon2 = point[index+1].lng.toRad();
        var dLon = (point[index + 1].lng - point[index].lng).toRad();

        // Find the bearing from this point to the next.
        var brng = Math.atan2(Math.sin(dLon) * Math.cos(lat2),
            Math.cos(lat1) * Math.sin(lat2) -
            Math.sin(lat1) * Math.cos(lat2) *
            Math.cos(dLon));

        var angDist = distance / 6371000;  // Earth's radius.

        // Calculate the destination point, given the source and bearing.
        lat2 = Math.asin(Math.sin(lat1) * Math.cos(angDist) +
            Math.cos(lat1) * Math.sin(angDist) *
            Math.cos(brng));

        lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(angDist) *
            Math.cos(lat1),
            Math.cos(angDist) - Math.sin(lat1) *
            Math.sin(lat2));

        if (isNaN(lat2) || isNaN(lon2)) return null;



        return new google.maps.LatLng(lat2.toDeg(), lon2.toDeg());
    }

    google.maps.Polyline.prototype.Distance = function () {
        var dist = 0;
        for (var i = 1; i < this.getPath().getLength(); i++) {
            dist += this.getPath().getAt(i).distanceFrom(this.getPath().getAt(i - 1));
        }
        return dist;
    }

    google.maps.LatLng.prototype.distanceFrom = function (newLatLng) {
        //var R = 6371; // km (change this constant to get miles)
        var R = 6378100; // meters
        var lat1 = this.lat();
        var lon1 = this.lng();
        var lat2 = newLatLng.lat();
        var lon2 = newLatLng.lng();
        var dLat = (lat2 - lat1) * Math.PI / 180;
        var dLon = (lon2 - lon1) * Math.PI / 180;
        var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
            Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) *
            Math.sin(dLon / 2) * Math.sin(dLon / 2);
        var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
        var d = R * c;
        return d;
    }

Answer 5

我想将 Daniel Vassalo 的答案移植到 iOS，但它无法正常工作，并且一些标记被放错位置，直到我更改

var dLon = (point.lng() - this.lng()).toRad();

为

var dLon = point.lng().toRad() - this.lng().toRad();

因此，如果有人无法弄清楚为什么标记放错了位置，请尝试一下，也许会有所帮助。