设置d3.geoPath（）的投影不能像记录那样工作

Question

我在D3中制作了很多地图，并且从来没有遇到这个问题，输出太小而无法看到它。我已经添加了一个小的geojson文件，可以使用各种其他工具轻松查看（e.g. here）。

看来，投影没有用d3.geoPath（）正确设置。 The API指定d3.geoPath（）接受投影参数，但是当我尝试使用此方法设置投影时（如下例所示），结果地图投影不正确。只有在使用d3.geoPath（）。projection（）方法设置投影后，我才能获得正确的结果。

这是文档中的错误还是我错过了什么？

//setup and map parameters 
 
var height = 300; 
 
var width = 300; 
 
var projection = d3.geoAlbers().scale(1000).translate([width/2, height/2]); 
 
var path = d3.geoPath(projection); 
 

 
//geoJSON data 
 
var geojson = 
 
{"type":"FeatureCollection","features":[ 
 
{"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[-86.910592,33.536105],[-86.907192,33.542204999999996],[-86.90539199999999,33.541305],[-86.901608,33.543456],[-86.895692,33.548805],[-86.89249199999999,33.550404],[-86.888392,33.549304],[-86.879772,33.553267999999996],[-86.868549,33.553418],[-86.8651,33.557134999999995],[-86.856129,33.562064],[-86.85159499999999,33.559404],[-86.848891,33.559805],[-86.852991,33.552104],[-86.85519099999999,33.543904999999995],[-86.855694,33.538151],[-86.860817,33.53405],[-86.850509,33.535693],[-86.83124699999999,33.544767],[-86.827029,33.534708],[-86.82383999999999,33.533389],[-86.826703,33.528081],[-86.826807,33.521107],[-86.822808,33.514319],[-86.81474899999999,33.502386],[-86.81411899999999,33.500078],[-86.816041,33.496234],[-86.823825,33.488839],[-86.825743,33.485408],[-86.82772299999999,33.477393],[-86.828558,33.472626999999996],[-86.82791,33.46967],[-86.833503,33.467552999999995],[-86.839366,33.463845],[-86.841534,33.460941],[-86.842309,33.465699],[-86.849758,33.466302],[-86.861663,33.456759],[-86.869367,33.4514],[-86.87749699999999,33.449382],[-86.884293,33.445453],[-86.88948599999999,33.441072999999996],[-86.890131,33.438437],[-86.899491,33.434508],[-86.908391,33.429308],[-86.922929,33.415512],[-86.925484,33.419897999999996],[-86.93114299999999,33.422801],[-86.93749199999999,33.421608],[-86.945352,33.425982999999995],[-86.946468,33.428407],[-86.937809,33.435314],[-86.925764,33.449968999999996],[-86.920859,33.454651999999996],[-86.92215,33.456643],[-86.927679,33.453849999999996],[-86.932965,33.449332],[-86.935435,33.446132],[-86.94133699999999,33.442150999999996],[-86.941301,33.445651999999995],[-86.942842,33.450103],[-86.946817,33.45017],[-86.95131599999999,33.45181],[-86.950279,33.458104],[-86.945494,33.463234],[-86.929693,33.478538],[-86.92935299999999,33.479858],[-86.920255,33.492874],[-86.92450699999999,33.493904],[-86.93110999999999,33.496843],[-86.933543,33.494935999999996],[-86.94144999999999,33.494743],[-86.944717,33.495934],[-86.946237,33.502279],[-86.946224,33.506071],[-86.941811,33.507621],[-86.937693,33.512206],[-86.92634,33.512381999999995],[-86.917255,33.517139],[-86.915435,33.519832],[-86.908779,33.518958999999995],[-86.903385,33.516537],[-86.898659,33.520165999999996],[-86.894459,33.526136],[-86.896992,33.530504],[-86.910592,33.536105]]]},"properties":{"a":1}} 
 
]} 
 

 
var svg = d3.select("#map"); 
 
svg.selectAll("path").data(geojson.features).enter().append("path").attr("fill","red").attr("d", path);

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

 
<svg height="300px" width="300px" id="map"> </svg>

Answer 1

您需要正确设置你的投影参数。比例因子1 000很小，可以显示一个小区域，如同您的示例。比例因子5万可能更合适。您还需要将地图正确居中。

您将需要找到靠近功能中心的点以正确居中地图。您可以通过使用google earth或其他方法手动执行此操作，以便在地理坐标中找到路径质心（不是svg坐标;但是，您可以通过翻译要素来找到svg质心来优化投影，但我没有使用该方法在我的答案虽然）。

随着阿尔伯斯投影，你应该集中在y轴和旋转的X轴：

var projection = d3.geoAlbers() 
    .rotate([-x,0]) 
    .center([0,y]) 
    .scale(k) 
    .translate([width/2,height/2]) 

你想，因为你在地图下旋转地球使用你的中央子午线的负值。请参阅this answer以获取Albers参数的更多图形说明

d3中的Albers投影具有默认的中心和旋转坐标。如果您没有设置中心坐标既有旋转又有中心，则地图将保留用于显示整个美国的默认参数;这将修改预期的投影。其他预测通常以d3中的[0,0]为中心，默认情况下是非洲沿岸。

我使用谷歌地球的眼睛中心坐标来使用此投影。我使用这里的中心观点是：

86.884 degrees West (-86.884 degrees East) 
33.507 degress North 

我也放大远远超出原来的缩放因子，采用10万而不是1 000这里是在您的数据投影：

//setup and map parameters 
 
var height = 300; 
 
var width = 300; 
 
var projection = d3.geoAlbers() 
 
    .scale(100000) 
 
    .translate([width/2, height/2]) 
 
    .rotate([86.884,0]) 
 
    .center([0,33.507]); 
 
var path = d3.geoPath(projection); 
 

 
//geoJSON data 
 
var geojson = 
 
{"type":"FeatureCollection","features":[ 
 
{"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[-86.910592,33.536105],[-86.907192,33.542204999999996],[-86.90539199999999,33.541305],[-86.901608,33.543456],[-86.895692,33.548805],[-86.89249199999999,33.550404],[-86.888392,33.549304],[-86.879772,33.553267999999996],[-86.868549,33.553418],[-86.8651,33.557134999999995],[-86.856129,33.562064],[-86.85159499999999,33.559404],[-86.848891,33.559805],[-86.852991,33.552104],[-86.85519099999999,33.543904999999995],[-86.855694,33.538151],[-86.860817,33.53405],[-86.850509,33.535693],[-86.83124699999999,33.544767],[-86.827029,33.534708],[-86.82383999999999,33.533389],[-86.826703,33.528081],[-86.826807,33.521107],[-86.822808,33.514319],[-86.81474899999999,33.502386],[-86.81411899999999,33.500078],[-86.816041,33.496234],[-86.823825,33.488839],[-86.825743,33.485408],[-86.82772299999999,33.477393],[-86.828558,33.472626999999996],[-86.82791,33.46967],[-86.833503,33.467552999999995],[-86.839366,33.463845],[-86.841534,33.460941],[-86.842309,33.465699],[-86.849758,33.466302],[-86.861663,33.456759],[-86.869367,33.4514],[-86.87749699999999,33.449382],[-86.884293,33.445453],[-86.88948599999999,33.441072999999996],[-86.890131,33.438437],[-86.899491,33.434508],[-86.908391,33.429308],[-86.922929,33.415512],[-86.925484,33.419897999999996],[-86.93114299999999,33.422801],[-86.93749199999999,33.421608],[-86.945352,33.425982999999995],[-86.946468,33.428407],[-86.937809,33.435314],[-86.925764,33.449968999999996],[-86.920859,33.454651999999996],[-86.92215,33.456643],[-86.927679,33.453849999999996],[-86.932965,33.449332],[-86.935435,33.446132],[-86.94133699999999,33.442150999999996],[-86.941301,33.445651999999995],[-86.942842,33.450103],[-86.946817,33.45017],[-86.95131599999999,33.45181],[-86.950279,33.458104],[-86.945494,33.463234],[-86.929693,33.478538],[-86.92935299999999,33.479858],[-86.920255,33.492874],[-86.92450699999999,33.493904],[-86.93110999999999,33.496843],[-86.933543,33.494935999999996],[-86.94144999999999,33.494743],[-86.944717,33.495934],[-86.946237,33.502279],[-86.946224,33.506071],[-86.941811,33.507621],[-86.937693,33.512206],[-86.92634,33.512381999999995],[-86.917255,33.517139],[-86.915435,33.519832],[-86.908779,33.518958999999995],[-86.903385,33.516537],[-86.898659,33.520165999999996],[-86.894459,33.526136],[-86.896992,33.530504],[-86.910592,33.536105]]]},"properties":{"a":1}} 
 
]} 
 

 
var svg = d3.select("#map"); 
 
svg.selectAll("path").data(geojson.features).enter().append("path").attr("fill","red").attr("d", path);

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

 
<svg height="300px" width="300px" id="map"> </svg>