插值后访问d3.line的y值 [英] Access y value of a d3.line after interpolation
问题描述
我正在使用 curveMonotoneX 插值绘制一条简单的线:
I am drawing a simple line using the curveMonotoneX interpolation :
const line = d3
.line()
.x((_, i) => xScale(i))
.y(d => yScale(d))
.curve(d3.curveMonotoneX);
除此之外，我想在有实际数据的线上添加点.由于进行了插值，我绘制的点并不完全在直线上，所以我切换到 d3.curveLinear ，而我的问题就消失了.
Besides that, I wanted to add points on the line where there is actual data. Because of the interpolation, the points I drawn were not exactly on the line so I switched to d3.curveLinear and my issues were gone.
但是，我想知道是否有一种现成的方法可以使用 x 值访问行的 y 值?
However, I was wondering is there a ready-to-use method to access the y value of a line using the x value ?
这样，无论插值方法如何，都可以在直线上绘制点.
This way, one could draw the points on the line regardless of the interpolation method.
推荐答案
Here's a quick example, wrapping the code here into a reusable function. It places a bunch of points on a fitted curve.
<!DOCTYPE html>
<meta charset="utf-8">
<style type="text/css">
.line {
fill: none;
stroke: orange;
stroke-width: 2;
}
.overlay {
fill: none;
pointer-events: all;
}
.dot {
fill: steelblue;
stroke: #fff;
}
</style>
<body>
<!-- Load in the d3 library -->
<script src="https://d3js.org/d3.v5.min.js"></script>
<script>
var margin = {
top: 50,
right: 50,
bottom: 50,
left: 50
},
width = window.innerWidth - margin.left - margin.right,
height = window.innerHeight - margin.top - margin.bottom;
var xScale = d3.scaleLinear()
.domain([0, 9])
.range([0, width]);
var yScale = d3.scaleLinear()
.domain([0, 10])
.range([height, 0]);
var line = d3.line()
.x(function(d, i) {
return xScale(i);
})
.y(function(d) {
return yScale(d);
})
.curve(d3.curveBasis);
var dataset = d3.range(10).map(function(d) {
return d3.randomUniform(1)() * 10;
})
var svg = d3.select("body").append("svg")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(d3.axisBottom(xScale));
svg.append("g")
.attr("class", "y axis")
.call(d3.axisLeft(yScale));
var path = svg.append("path")
.datum(dataset)
.attr("class", "line")
.attr("d", line);
svg.selectAll(".dot")
.data(d3.range(0, 9.5, 0.5))
.enter()
.append("circle")
.attr("cx", (d) => xScale(d))
.attr("cy", (d) => yValueForX(d))
.attr("r", 5)
.attr("class", "dot")
function yValueForX(xCor){
var x = xScale(xCor),
pathEl = path.node(),
pathLength = pathEl.getTotalLength();
var beginning = x, end = pathLength, target;
while (true) {
target = Math.floor((beginning + end) / 2);
pos = pathEl.getPointAtLength(target);
if ((target === end || target === beginning) && pos.x !== x) {
break;
}
if (pos.x > x) end = target;
else if (pos.x < x) beginning = target;
else break; //position found
}
return pos.y;
}
</script>
</body>这篇关于插值后访问d3.line的y值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
