D3.js geoWagner4()函数

The geoWagner4() function is a projection in the D3.js library based on the Wagner IV projection. The Wagner IV is a pseudo-cylindrical projection, which means that it preserves the shape and area of features on the map while distorting their distances and angles. The geoWagner4() function allows you to create a map projection in this style.

Syntax

The syntax for the geoWagner4() function is as follows:

d3.geoWagner4()

Usage

To use the geoWagner4() projection, you first need to define it and then apply it to your map with the D3.js projection() method. Here is an example:

var projection = d3.geoWagner4()
    .scale(100)
    .translate([width/2, height/2])
    .precision(0.1);

In this example, we define a new geoWagner4() projection with a scale of 100, a translation of [width/2, height/2], and a precision of 0.1. We then apply this projection to our map with the projection() method, like so:

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

svg.selectAll("path")
    .data(features)
    .enter()
    .append("path")
    .attr("d", path);

In this code, we are creating a new path generator with the geoPath() function and passing it our projection with the projection() method. We then use this path generator to render our map data as SVG paths with the enter() and append() methods.

Parameters

The geoWagner4() function takes no parameters.

Return Value

The geoWagner4() function returns a new projection object that can be used with the D3.js projection() method.

Example

Here is an example of a geoWagner4() projection in action:

var width = 500;
var height = 500;

var svg = d3.select("body")
    .append("svg")
    .attr("width", width)
    .attr("height", height);

var projection = d3.geoWagner4()
    .scale(100)
    .translate([width/2, height/2])
    .precision(0.1);

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

d3.json("path/to/json", function(error, topology) {
  var features = topojson.feature(topology, topology.objects.collection).features;

  svg.selectAll("path")
      .data(features)
      .enter()
      .append("path")
      .attr("d", path)
      .style("fill", "steelblue")
      .style("stroke", "white");
});

In this example, we are creating a new geoWagner4() projection with a scale of 100 and a translation of [width/2, height/2]. We then load in a JSON file containing our map data with the d3.json() function, create a new geoPath() generator with our projection, and use it to render our map data as SVG paths with the enter() and append() methods. We also style these paths with CSS properties like fill and stroke.