How to reproduce GPS tracks with javascript

With the advent of the mobile Internet era, we have become inseparable from various map applications, such as Baidu Maps, Amap, Google Maps, etc. These map applications not only facilitate our travels, but also record our trajectories. In fields such as sports or logistics, the trajectory playback function is particularly important. So how to implement the track playback function? This article will introduce you to the method of reproducing GPS tracks through JavaScript.

1. Prerequisite knowledge

Before we start to introduce how to realize GPS trajectory reproduction, we need to understand several prerequisite knowledge:

(1)GPS positioning principle

The full name of GPS is "Global Positioning System", which is the global satellite positioning system. The principle is to transmit signals through satellites, receive terminal receivers to measure the signals, and then calculate the distance of the terminal receivers relative to the satellites, and then calculate the location information of the terminals.

(2) Trajectory data format

Before realizing trajectory reproduction, we need to prepare trajectory data. Trajectory data generally contains information such as timestamp, longitude, latitude, speed, etc. The format can be CSV, JSON, etc., depending on the specific situation.

(3) Map API

Map API refers to services that provide map data and related functions. When realizing GPS trajectory reproduction, we need to use the related functions of the map API, such as map rendering, trajectory drawing, etc.

2. Implementation steps

1. Prepare data

First, we need to prepare trajectory data. Here we take the JSON format as an example:

{
   "points": [
      { "lng": 116.397428, "lat": 39.90923, "time": 1601463615000 },
      { "lng": 116.404064, "lat": 39.915387, "time": 1601463630000 },
      { "lng": 116.407633, "lat": 39.91258, "time": 1601463645000 },
      { "lng": 116.410326, "lat": 39.904023, "time": 1601463660000 },
      ...
   ]
}

Among them, the points array stores the longitude, latitude and timestamp information of the track points.

2. Introducing the map API

In the process of realizing trajectory reproduction, we need to use the relevant functions provided by the map API. Here we take Baidu Map API as an example and introduce the code as follows:

<script type="text/javascript" src="http://api.map.baidu.com/api?v=2.0&ak={your-app-key}"></script>

Among them, {your-app-key} needs to be replaced with your application AK.

3. Create a map

Next, we need to create a map container and initialize the map. The code is as follows:

<div id="map-container" style="width: 100%; height: 100%;"></div>

<script type="text/javascript">
   // 创建地图实例
   var map = new BMap.Map("map-container");
   
   // 初始化地图，设置中心点和缩放级别
   map.centerAndZoom(new BMap.Point(116.404, 39.915), 15);
</script>

In the code, we create a div container with the ID "map-container" for rendering the map. Then, use the BMap.Map method to create a map instance, and use the centerAndZoom method to initialize the map and set the center point and zoom level.

4. Draw the trajectory

Next, we need to draw the trajectory points on the map. The code is as follows:

<script type="text/javascript">
   // 绘制轨迹
   function drawTrace(points) {
      var polyline = new BMap.Polyline([], { strokeColor: "#FF0000", strokeWeight: 3, strokeOpacity: 0.5 }); // 创建折线对象
      for (var i = 0; i < points.length; i++) {
         var point = new BMap.Point(points[i].lng, points[i].lat); // 创建坐标点
         polyline.getPath().push(point); // 添加坐标点
      }
      map.addOverlay(polyline); // 将折线添加到地图中
   }
   
   // 加载轨迹数据并绘制轨迹
   function loadTraceData(traceUrl) {
      $.getJSON(traceUrl, function (data) {
         var points = data.points;
         drawTrace(points);
      });
   }
   
   // 调用加载轨迹数据方法
   loadTraceData("trace.json");
</script>

In the code, we first define the drawTrace method for drawing trajectories. This method first creates a BMap.Polyline object, then traverses the track point array, converts each point into a BMap.Point object, and adds it to the path of the polyline object. , and finally add the polyline object to the map.

Next, we define the loadTraceData method, which is used to load trajectory data and draw trajectories. This method uses the $.getJSON method to load the trajectory data in JSON format, and calls the drawTrace method to draw the trajectory.

Finally, we call the loadTraceData method and pass in the URL of the trace data.

5. Track playback

Finally, we need to implement the track playback function. The code is as follows:

<script type="text/javascript">
   // 轨迹回放
   function tracePlayback(points) {
      var index = 0;
      var timer;
      var moveMarker = new BMap.Marker(points[0]);
      map.addOverlay(moveMarker);
      map.panTo(points[0]);
      moveMarker.setAnimation(BMAP_ANIMATION_BOUNCE);
      timer = setInterval(function () {
         if (index < points.length - 1) {
            index++;
            var currentPoint = new BMap.Point(points[index].lng, points[index].lat);
            moveMarker.setPosition(currentPoint);
            map.panTo(currentPoint);
         } else {
            clearInterval(timer);
            moveMarker.setAnimation(null);
         }
      }, 200);
   }
   
   // 加载轨迹数据并绘制轨迹
   function loadTraceData(traceUrl) {
      $.getJSON(traceUrl, function (data) {
         var points = data.points;
         drawTrace(points);
         tracePlayback(points);
      });
   }
   
   // 调用加载轨迹数据方法
   loadTraceData("trace.json");
</script>

In the code, we first define the tracePlayback method to implement the trace playback function. This method uses the BMap.Marker object to create a moving marker, and uses the setAnimation method to set the animation effect of the marker. Then, use the setInterval method to periodically update the marker's position to implement the track playback function.

Next, we called the tracePlayback method in the loadTraceData method to achieve trace playback.

Finally, we call the loadTraceData method and pass in the URL of the trace data.

3. Summary

This article introduces the method of reproducing GPS tracks through JavaScript, including five steps: preparing data, introducing map API, creating maps, drawing tracks and track playback. Implementing the trajectory playback function can help us better understand the trajectory direction, so as to better perform data analysis, optimization solutions, etc.

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