設置d3.geoPath（）的投影不能像記錄那樣工作

Question

我在D3中製作了很多地圖，並且從來沒有遇到這個問題，輸出太小而無法看到它。我已經添加了一個小的geojson文件，可以使用各種其他工具輕鬆查看（e.g. here）。

看來，投影沒有用d3.geoPath（）正確設置。 The API指定d3.geoPath（）接受投影參數，但是當我嘗試使用此方法設置投影時（如下例所示），結果地圖投影不正確。只有在使用d3.geoPath（）。projection（）方法設置投影后，我才能獲得正確的結果。

這是文檔中的錯誤還是我錯過了什麼？

//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

您需要正確設置你的投影參數。比例因子1 000很小，可以顯示一個小區域，如同您的示例。比例因子5萬可能更合適。您還需要將地圖正確居中。

您將需要找到靠近功能中心的點以正確居中地圖。您可以通過使用google earth或其他方法手動執行此操作，以便在地理座標中找到路徑質心（不是svg座標;但是，您可以通過翻譯要素來找到svg質心來優化投影，但我沒有使用該方法在我的答案雖然）。

隨着阿爾伯斯投影，你應該集中在y軸和旋轉的X軸：

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

你想，因爲你在地圖下旋轉地球使用你的中央子午線的負值。請參閱this answer以獲取Albers參數的更多圖形說明

d3中的Albers投影具有默認的中心和旋轉座標。如果您沒有設置中心座標既有旋轉又有中心，則地圖將保留用於顯示整個美國的默認參數;這將修改預期的投影。其他預測通常以d3中的[0,0]爲中心，默認情況下是非洲沿岸。

我使用谷歌地球的眼睛中心座標來使用此投影。我使用這裏的中心觀點是：

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

我也放大遠遠超出原來的縮放因子，採用10萬而不是1 000這裏是在您的數據投影：

//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>