在d3地图投影周围创建弯曲的边框 [英] Create a curved border around a d3 map projection

问题描述

我已使用

I have created a world map in d3 using the geoNaturalEarth1() shown here. I used a geojson map of the world with this projection to get the map as shown in the code below. However, this shows the countries floating in space without a border. I'd like to draw a border around the map projection, so that it looks more like a map. The border would be the flat top/bottom, curved sides as shown in the projection image. Is this possible, and how could I go about doing it?

var projection = d3.geoNaturalEarth1()
    .translate([w/2, h/2])
    .scale(247)
    .center([0,0]);

var path = d3.geoPath().projection(projection);

d3.json('map.geojson').then(function(world) {

    svg.selectAll(".emissions_path")
        .data(world.features)
        .enter().append("path")
        .attr('fill', '#fff')
        .attr("d", path)
        .style('stroke', 'black')
        .style('stroke-width', '0.5px');

推荐答案

您可以向路径生成器提供类型为 Sphere 的geojson:

You can provide geojson with type Sphere to the path generator:

还支持Sphere类型，这对于呈现地球轮廓；球体没有坐标.(文档)

这看起来像:

var outline = {type:"Sphere"}

它可以直接传递给路径生成器:

And it can be passed directly to the path generator:

var context = d3.select("canvas").node().getContext("2d"),
    projection = d3.geoNaturalEarth1()
      .scale(70)
      .translate([200,100])
    path = d3.geoPath()
      .context(context)
      .projection(projection);

d3.json("https://unpkg.com/world-atlas@1/world/110m.json", function(error, world) {
  if (error) throw error;

  context.beginPath();
  context.fillStyle = "lightgreen";
  path(topojson.feature(world, world.objects.land));
  context.fill();
  
  context.beginPath();
  context.strokeStyle = "#ccc";
  path({type: "Sphere"})
  context.stroke();
  
});

<canvas width="500" height="300"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://unpkg.com/topojson-client@3"></script>

顺便说一句，还有 d3.geoGraticule ，允许定期绘制子午线和平行线:

As an aside, there is also d3.geoGraticule, which allows for drawing meridians and parallels at regular intervals:

var context = d3.select("canvas").node().getContext("2d"),
        projection = d3.geoNaturalEarth1()
          .scale(70)
          .translate([200,100])
        path = d3.geoPath()
          .context(context)
          .projection(projection);

    d3.json("https://unpkg.com/world-atlas@1/world/110m.json", function(error, world) {
      if (error) throw error;

      context.beginPath();
      context.fillStyle = "lightgreen";
      path(topojson.feature(world, world.objects.land));
      context.fill();
  
      context.beginPath();
      context.strokeStyle = "#eee";
      path(d3.geoGraticule10())
      context.stroke();
      
      context.beginPath();
      context.strokeStyle = "#000";
      path({type:"Sphere"})
      context.stroke();        
      
    });

<canvas width="500" height="300"></canvas>
    <script src="https://d3js.org/d3.v4.min.js"></script>
    <script src="https://unpkg.com/topojson-client@3"></script>

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