projection([lat,lng])始终返回null [英] projection([lat,lng]) keeps returning null
本文介绍了projection([lat,lng])始终返回null的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我试图使用albersUsa投影将几个点从GeoJSON文件映射到地图上。我的代码如下,但它未能添加 cx
和 cy
属性到 circle
元素:
I'm trying to map several points from a GeoJSON file onto a map using the albersUsa projection. My code is as follows, but it fails to add the cx
and cy
attributes to the circle
elements:
var width = 960, height = 500;
// set projection
var projection = d3.geo.albersUsa()
.scale(1000)
.translate([width / 2, height / 2]);
// create path variable
var path = d3.geo.path().projection(projection);
d3.json("us.json", function(error, topo) {
states = topojson.feature(topo, topo.objects.states).features
// create svg variable
var svg = d3.select("#body").append("svg")
.attr("width", width)
.attr("height", height);
// add states from topojson
svg.append("g").attr("class", "feature").selectAll("path")
.data(states).enter()
.append("path")
.attr("class", "feature")
.attr("d", path);
// put border around states
svg.append("g").attr("class", "mesh").append("path")
.datum(topojson.mesh(topo, topo.objects.states, function(a, b) { return a !== b; }))
.attr("class", "mesh")
.attr("d", path);
d3.json("data/bhutan.json", function(error, bhutan) {
// add circles to svg
svg.selectAll("circle")
.data(bhutan.features)
.enter()
.append("circle")
.attr("class", "bhutan")
.attr("cx", function(d) {
var longitude = d.geometry.coordinates[0];
var latitude = d.geometry.coordinates[1];
return projection(latitude);
})
.attr("cy", function(d) {
var longitude = d.geometry.coordinates[0];
var latitude = d.geometry.coordinates[1];
return projection(longitude);
})
.attr("r", "8px");
});
和我的JSON:
{
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [39.13, -84.48845]
},
"properties": {
"state": "Ohio",
"city": "2816 Cincinnati",
"arrivals": "1"
}
}, {
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [32.44874, -99.73314]
},
"properties": {
"state": "Texas",
"city": "Abilene",
"arrivals": "178"
}
}, {
…
}]
}
任何人都可以帮我找出我做错了什么?
Can anyone help me figure out what I'm doing wrong?
推荐答案
你调用投影不正确 - 需要给一对坐标:
You're calling the projection incorrectly -- it needs to be given a pair of coordinates:
.attr("cx", function(d) {
var longitude = d.geometry.coordinates[1];
var latitude = d.geometry.coordinates[0];
return projection([longitude, latitude])[0];
})
.attr("cy", function(d) {
var longitude = d.geometry.coordinates[1];
var latitude = d.geometry.coordinates[0];
return projection([longitude, latitude])[1];
})
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