D3 albersUsa投影功能返回null [英] D3 albersUsa projection funtion return null

问题描述

我是D3的新手，我正在尝试在地图上设置点.

I'm pretty new to D3 and I'm trying to set point on a map.

使用此代码创建投影时，我感到很困惑:

I'm confused as I created a projection with this code:

var projection = d3.geo
      .albersUsa()
      .scale(500)
      .translate([el.clientWidth / 2, el.clientHeight / 2]);

我使用此投影来绘制地图，并且效果很好.

I use this projection to draw a map and it works fine.

但是无论何时我调用projection([10, 20])，它都会返回null，无论我传入的值是什么.

But then whenever I call projection([10, 20]) it returns null whichever values I'm passing in.

我的错误是什么?

推荐答案

来自文档

#

[…] 如果指定的位置没有定义的投影位置，例如当该位置在投影的剪切范围之外时，则可能返回null.

[…] May return null if the specified location has no defined projected position, such as when the location is outside the clipping bounds of the projection.

Albers USA投影仅在其边界内定义，对于定义明确的区域之外的坐标将产生null.

The Albers USA projection is defined only within its borders and will yield null for coordinates outside the well-defined area.

请参见使用无效的[10,20]和有效点[-110,40]调用projection(location)的以下比较:

See this comparison of calls to projection(location) using [10,20], which is not valid, and [-110,40], which is a valid point:

var projection = d3.geo
      .albersUsa()
      .scale(500)
      .translate([960, 500]);
      
d3.selectAll("p")
    .data([[10,20],[-110,40]])
  .enter().append("p")
    .text(function(d) { return d + ": " + projection(d); });

 

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>

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