javascript - d3 v4 geo 绘制边界反转

Question

当我在 SVG 元素中绘制百慕大三 Angular 形时，比例不是我所期望的(三 Angular 形应该延伸到框的边缘)并且填充是向后的(而不是绘制三 Angular 形，它绘制了一个切掉三 Angular 形的正方形).

var geojson = {
  "features": [
    {
      "type": "Feature",
      "properties": {
        "name": "Bermuda Triangle",
        "area": 1150180
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [-64.73, 32.31],
            [-80.19, 25.76],
            [-66.09, 18.43],
            [-64.73, 32.31]
          ]
        ]
      }
    }
  ],
  "type":"FeatureCollection"
};

var width = 480;
var height = 480;

var svg = d3.select("body").append("svg")
  .attr("width", width)
  .attr("height", height)
  .attr("style", "border: 2px solid black");

var projection = d3.geoMercator().fitSize([width, height], geojson);
var path = d3.geoPath().projection(projection);

svg.selectAll('path')
  .data(geojson.features)
  .enter()
  .append('path')
  .attr('d', path)
  .style("fill", "red")
  .style("stroke-width", "1")
  .style("stroke", "black");

<script src="//d3js.org/d3.v4.js"></script>

我做错了什么？

Answer 1

让我们改变一下:

[
    [-64.73, 32.31],
    [-80.19, 25.76],
    [-66.09, 18.43],
    [-64.73, 32.31]
]

对此:

[
    [-64.73, 32.31],
    [-66.09, 18.43],
    [-80.19, 25.76],
    [-64.73, 32.31]
]

这似乎是一个很小的变化，但却是一个重要的变化:D3 要求多边形顶点按顺时针顺序排列。

根据API :

Spherical polygons also require a winding order convention to determine which side of the polygon is the inside: the exterior ring for polygons smaller than a hemisphere must be clockwise, while the exterior ring for polygons larger than a hemisphere must be anticlockwise. (emphasis mine)

此外，这是 Bostock(D3 创建者)制作的一个有趣的 bl.ocks，从教学上解释了您的问题:https://bl.ocks.org/mbostock/a7bdfeb041e850799a8d3dce4d8c50c8

这是您进行了更改(并删除了 fitSize)的代码:

var geojson = {
  "features": [{
    "type": "Feature",
    "properties": {
      "name": "Bermuda Triangle",
      "area": 1150180
    },
    "geometry": {
      "type": "Polygon",
      "coordinates": [
        [
          [-64.73, 32.31],
          [-66.09, 18.43],
          [-80.19, 25.76],
          [-64.73, 32.31]
        ]
      ]
    }
  }],
  "type": "FeatureCollection"
};

var width = 480;
var height = 480;

var svg = d3.select("body").append("svg")
  .attr("width", width)
  .attr("height", height)
  .attr("style", "border: 2px solid black");

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

svg.selectAll('path')
  .data(geojson.features)
  .enter()
  .append('path')
  .attr('d', path)
  .style("fill", "red")
  .style("stroke-width", "1")
  .style("stroke", "black");

<script src="//d3js.org/d3.v4.js"></script>