Detailed explanation of the steps to create a logistics map using D3.js-JS Tutorial-php.cn

This time I will give you a detailed explanation of the steps for using D3.js to create a logistics map. What are the precautions for using D3.js to create a logistics map? The following is a practical case, let’s take a look together. take a look.

Production ideas

A map of China needs to be drawn as a background.
The latitude and longitude coordinates of major cities are required to draw the starting and ending points of road sheets.
The city that receives the logistics order draws a flashing mark.
The target city that already has a logistics order will no longer draw a route.
Every time a new logistics order is generated, there will be an animation effect of the mark moving along the route to the target.
The data after drawing needs to be cleaned up to reduce the resource usage of the browser.

Start coding

1. Create a web page template

Load D3JS. In order to facilitate debugging, directly download the d3.js file locally. When actually using it, you can change it to the loading path. Note that the V4 version of D3 is used, which is different from the V3 version.

Create a p-block, ready for drawing.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf8">
    <script type="text/javascript" src="../../static/d3/d3.js"></script>
    <title>地图</title>
  </head>
  <body>
    <p class="fxmap">
    </p>
  </body>
  <script type="text/javascript"></script>
</html>

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Create SVG, place all the following codes in <script></script>

var width=1000 , height=800; // 定义SVG宽高
var svg = d3.select("body p.fxmap")
            .append("svg")
            .attr("width", "width) 
            .attr("height", height)
            .style("background","#000"); //

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Create SVG graphics groupings to prepare for calling

gmp, saves the background map and starting point markers.
mline, saves the connection between the starting point and the target, as well as the target point.
button, button for testing

gmap = svg.append("g").attr("id", "map").attr("stroke", "white").attr("stroke-width",1);
    mline = svg.append("g").attr("id", "moveto").attr("stroke", "#FFF").attr("stroke-width", 1.5).attr("fill","#FFF");
    button = svg.append("g").attr("id", "button").attr("stroke", "white").attr("stroke-width", 1).attr("fill", "white");

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Create projection function

Longitude and latitude cannot be used directly for drawing and need to be converted into plane coordinates. d3js provides a relatively rich range of projection methods. In this example, the geoEquirectangular() method is used.
projection is a method for converting longitude and latitude into plane coordinates
path is a method for converting longitude and latitude into point coordinates for connecting lines (saving you from writing functions yourself) Construct path path)

var projection = d3.geoEquirectangular()
              .center([465,395]) // 指定投影中心，注意[]中的是经纬度
              .scale(height)
              .translate([width / 2, height / 2]);
var path = d3.geoPath().projection(projection);

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Create marker tags for multiple connection endpoint calls

Since there will be multiple end points of the logistics line, they are all called in a marker.
This mark is composed of a circular outer ring in the middle. The flashing effect of the outer ring is created separately.

marker = svg.append("defs")
          .append("marker")
          .append("marker")
          .attr("id", "pointer")
          .attr("viewBox","0 0 12 12")  // 可见范围
          .attr("markerWidth","12")    // 标记宽度
          .attr("markerHeight","12")    // 标记高度
          .attr("orient", "auto")     //
          .attr("markerUnits", "strokeWidth") // 随连接线宽度进行缩放
          .attr("refX", "6")       // 连接点坐标
          .attr("refY", "6")
    // 绘制标记中心圆
    marker.append("circle")
        .attr("cx", "6")
        .attr("cy", "6")
        .attr("r", "3")
        .attr("fill", "white");
    // 绘制标记外圆，之后在timer()中添加闪烁效果
    marker.append("circle")
        .attr("id", "markerC")
        .attr("cx", "6")
        .attr("cy", "6")
        .attr("r", "5")
        .attr("fill-opacity", "0")
        .attr("stroke-width", "1")
        .attr("stroke", "white");

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Draw a map of China and mark the starting point (Changsha)

The latitude and longitude set used in the map is china.json. There are many files on the Internet

// 记录长沙坐标
    var changsha = projection([112.59,28.12]);
    // 读取地图数据，并绘制中国地图
    mapdata = [];
    d3.json('china.json', function(error, data){
      if (error)
        console.log(error);
      // 读取地图数据
      mapdata = data.features;
      // 绘制地图
      gmap.selectAll("path")
        .data(mapdata)
        .enter()
        .append("path")
        .attr("d", path);
      // 标记长沙
      gmap.append("circle").attr("id","changsha")
        .attr("cx", changsha[0])
        .attr("cy", changsha[1])
        .attr("r", "6")
        .attr("fill", "yellow")
      gmap.append("circle").attr("id","changshaC")
        .attr("cx", changsha[0])
        .attr("cy", changsha[1])
        .attr("r", "10")
        .attr("stroke-width", "2")
        .attr("fill-opacity", "0");
    });

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Create a method to draw a line from the specified starting point to the end point, and draw markers at the network points.

The method requires inputting the destination city name (city) and longitude and latitude (data)
Call the previously established project() method to convert the destination longitude and latitude into plane coordinates.
Calculate the distance between the starting point (Changsha) and the end point as line length and animation time parameters.
Draw a circular mark on the line and implement a moving animation from the starting point to the end point
After the mark moves to the end point, it is deleted ,save resources.
If the line point has been drawn before, no line will be drawn, only the moving mark will be drawn.
Every time a logistics order is processed, the city record is 1.

// 创建对象，保存每个城市的物流记录数量
    var citylist = new Object();
    // 创建方法，输入data坐标，绘制发射线
    var moveto = function(city, data){
      var pf = {x:projection([112.59,28.12])[0], y:projection([112.59,28.12])[1]};
      var pt = {x:projection(data)[0], y:projection(data)[1]};
      var distance = Math.sqrt((pt.x - pf.x)**2 + (pt.y - pf.y)**2);
      if (city in citylist){
        citylist[city]++;
      }else{
        mline.append("line")
            .attr("x1", pf.x)
            .attr("y1", pf.y)
            .attr("x2", pt.x)
            .attr("y2", pt.y)
            .attr("marker-end","url(#pointer)")
            .style("stroke-dasharray", " "+distance+", "+distance+" ")
            .transition()
            .duration(distance*30)
            .styleTween("stroke-dashoffset", function(){
              return d3.interpolateNumber(distance, 0);
            });
        citylist[city] = 1;
      };
      mline.append("circle")
        .attr("cx", pf.x)
        .attr("cy", pf.y)
        .attr("r", 3)
        .transition()
        .duration(distance*30)
        .attr("transform", "translate("+(pt.x-pf.x)+","+(pt.y-pf.y)+")")
        .remove();
    };

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Create an animation queue instance to achieve the flashing effect of the outer circle of the mark

var scale = d3.scaleLinear();
    scale.domain([0, 1000, 2000])
      .range([0, 1, 0]);
    var start = Date.now();
    d3.timer(function(){
      var s1 = scale((Date.now() - start)%2000);
      // console.log(s1);
      gmap.select("circle#changshaC")
        .attr("stroke-opacity", s1);
      marker.select("circle#markerC")
        .attr("stroke-opacity", s1);
    });

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Create a test button and test target city data

var cityordinate = {
      '哈尔滨':[126.5416150000,45.8088260000],
      '石家庄':[116.46,39.92],
      '北京':[116.39564503787867,39.92998577808024],
      '上海':[121.480539,31.235929],
      '广州':[113.271431,23.135336],
      '重庆':[106.558434,29.568996],
      '青岛':[120.38442818368189,36.10521490127382],
      '福州':[119.30347,26.080429],
      '兰州':[103.840521,36.067235],
      '贵阳':[106.636577,26.653325],
      '成都':[104.081534,30.655822],
      '西安':[108.946466,34.347269],
      '长春':[125.3306020000,43.8219540000],
      '台湾':[120.961454,23.80406],
      '呼和浩特':[111.7555090000,40.8484230000],
      '澳门':[113.5494640000,22.1929190000],
      '武汉':[114.3115820000,30.5984670000],
      '昆明':[102.71460113878045,25.049153100453159],
      '乌鲁木齐':[87.56498774111579,43.84038034721766],
      '益阳':[112.36654664522563,28.58808777988717],
      '南京':[118.77807440802562,32.05723550180587],
      '武昌':[114.35362228468498,30.56486029278519],
    };
    // 随机获得目标城市
    var cityname = [], total = 0;
    for (var key in cityordinate){
      cityname[total++] = key;
    };
    
    // 创建操作按钮，每次点击发射一条物流线
    button.append("circle")
        .attr("cx", width*0.9)
        .attr("cy", height*0.8)
        .attr("r", width/20)
        .attr("text","click")
        .attr("fill", "grey");
    button.append("text")
        .attr("x", width*0.87)
        .attr("y", height*0.81)
        .style("font-size", "30px")
        .text("click");
    button.on("click", function(){
      var _index = ~~(Math.random() * total);
      moveto(cityname[_index], cityordinate[cityname[_index]]);
    });

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I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the PHP Chinese website!