d3.js geoEckert4()用法及代码示例

D3.js是一个JavaScript库，用于在Web浏览器中生成动态的交互式数据可视化。它利用可伸缩矢量图形，HTML5和级联样式表标准。

d3.js中的geoEckert4()函数用于绘制Eckert IV投影，该投影是equal-area伪圆柱图投影。极线的长度是赤道长度的一半，而经度线是半椭圆或椭圆的一部分。

用法:

d3.geoEckert4()

参数：此方法不接受任何参数。

返回值：此方法根据给定的JSON数据创建Eckert4投影。

范例1：以下示例对Eckert4进行投影，其中心为(0,0)，并且不旋转。

HTML

<!DOCTYPE html>  
<html lang="en">  
  
<head>  
    <meta charset="UTF-8" />  
    <meta name="viewport"
        content="width=device-width,  
                initial-scale=1.0"/>    
    <script src= 
        "https://d3js.org/d3.v4.js"> 
    </script> 
    <script src= 
"https://d3js.org/d3-geo-projection.v2.min.js"> 
    </script>   
</head>  
  
<body>  
    <div style="width:700px; height:600px;">  
        <svg width="700" height="550">  
        </svg>  
    </div>  
      
    <script> 
        var svg = d3.select("svg"), 
            width = +svg.attr("width"), 
            height = +svg.attr("height"); 
  
        // geoEckert Iv  projection 
        // Center(0,0) and no rotation 
        var gfg = d3.geoEckert4() 
            .scale(width / 1.5 / Math.PI) 
            .rotate([0,0]) 
            .center([0,0]) 
            .translate([width / 2, height / 2]) 
  
        // Loading the json data 
        d3.json("https://raw.githubusercontent.com/" 
            + "janasayantan/datageojson/master/world.json",  
            function(data){ 
                // Draw the map 
                svg.append("g") 
                   .selectAll("path") 
                   .data(data.features) 
                   .enter().append("path") 
                   .attr("fill", "GREY") 
                   .attr("d", d3.geoPath() 
                       .projection(gfg) 
                    ).style("stroke", "#ffff") 
        }) 
    </script> 
</body>  
  
</html>

输出：

Eckert IV投影，中心为(0,0)，旋转为0

范例2：以下示例对Eckert4进行世界投影，中心为(0,0)，顺时针旋转20度。

HTML

<!DOCTYPE html>  
<html lang="en">  
  
<head>  
    <meta charset="UTF-8" />  
    <meta name="viewport"
        content="width=device-width,  
                initial-scale=1.0"/> 
    <script src= 
        "https://d3js.org/d3.v4.js"> 
    </script> 
    <script src= 
"https://d3js.org/d3-geo-projection.v2.min.js"> 
    </script> 
</head>  
  
<body>  
    <div style="width:700px; height:600px;">  
        <center>  
            <h3 style="color:black">  
            Eckert IV Projection of World 
            </h3>   
        </center> 
        <svg width="700" height="400">  
        </svg>  
    </div>  
      
    <script> 
        var svg = d3.select("svg"), 
            width = +svg.attr("width"), 
            height = +svg.attr("height"); 
  
        // geoEckert IV  projection 
        // Center(0,0) and rotating 20  
        // degree clockwise 
        var gfg = d3.geoEckert4() 
            .scale(width / 1.5 / Math.PI) 
            .rotate([20,0]) 
            .center([0,0]) 
            .translate([width / 2, height / 2]) 
  
        // Loading the json data 
        d3.json("https://raw.githubusercontent.com/" 
            + "janasayantan/datageojson/master/world.json",  
            function(data) { 
                // Draw the map 
                svg.append("g") 
                   .selectAll("path") 
                   .data(data.features) 
                   .enter().append("path") 
                   .attr("fill", "GREY") 
                   .attr("d", d3.geoPath() 
                       .projection(gfg) 
                   ).style("stroke", "#ffff") 
        }) 
    </script> 
</body>  
  
</html>

输出：

旋转的Eckert IV投影

相关用法

注：本文由纯净天空筛选整理自jana_sayantan大神的英文原创作品 D3.js geoEckert4() Function。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。