标签外弧(饼图)d3.js [英] Label outside arc (Pie chart) d3.js
问题描述
I'm new to d3.js and I"m trying to make a Pie-chart with it. I have only one problem: I can't get my labels outside my arcs... The labels are positioned with arc.centroid
arcs.append("svg:text")
.attr("transform", function(d) {
return "translate(" + arc.centroid(d) + ")";
})
.attr("text-anchor", "middle")
Who can help me with this?
I can solve that problem - with trigonometry :).
See fiddle: http://jsfiddle.net/nrabinowitz/GQDUS/
Basically, calling arc.centroid(d)
returns an [x,y]
array. You can use the Pythagorean Theorem to calculate the hypotenuse, which is the length of the line from the center of the pie to the arc centroid. Then you can use the calculations x/h * desiredLabelRadius
and y/h * desiredLabelRadius
to calculate the desired x,y
for your label anchor:
.attr("transform", function(d) {
var c = arc.centroid(d),
x = c[0],
y = c[1],
// pythagorean theorem for hypotenuse
h = Math.sqrt(x*x + y*y);
return "translate(" + (x/h * labelr) + ',' +
(y/h * labelr) + ")";
})
The only downside here is that text-anchor: middle
isn't a great choice anymore - you'd be better off setting the text-anchor
based on which side of the pie we're on:
.attr("text-anchor", function(d) {
// are we past the center?
return (d.endAngle + d.startAngle)/2 > Math.PI ?
"end" : "start";
})
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