在d3中,如何从SVG行获取插入线数据? [英] In d3, how to get the interpolated line data from a SVG line?
问题描述
我用D3大致显示一个折线图(给定比例函数 x
, y
浮点数组 data
):
var line = d3.svg。 line()
.interpolate(basis)
.x(function(d,i){return x(i);})
.y (d);});
d3.select('。line')。attr('d',line(data));
现在,我想知道给定水平像素位置的线的垂直高度。 data
数组比像素的数据点少,显示的行是 interpolated ,因此不直接推导出行的高度
任何提示?
您需要对由 getPointAtLength
返回的数据进行某种搜索。 (请参阅 https://developer.mozilla.org/en-US/docs/ DOM / SVGPathElement 。)
// Line
var line = d3.svg.line
.interpolate(basis)
.x(function(d){return i;})
.y(function(d,i){return 100 * Math.sin(i )+ 100;});
//追加DOM的路径
d3.select(svg#chart)//或任何你的SVG容器是
.append(svg:path )
.attr(d,line([0,10,20,30,40,50,60,70,80,90,100]))
.attr(id,myline );
//获取坐标
function findYatX(x,linePath){
function getXY(len){
var point = linePath.getPointAtLength(len);
return [point.x,point.y];
}
var curlen = 0;
while(getXY(curlen)[0]< x){curlen + = 0.01; }
return getXY(curlen);
}
console.log(findYatX(5,document.getElementById(myline)));
对我来说,这会返回[5.000403881072998,140.6229248046875]。
这个搜索函数 findYatX
远不是有效的(在 O(n)时间运行) / p>
I display a line chart with D3 with roughly the following code (given the scale functions x
, y
and the float array data
):
var line = d3.svg.line()
.interpolate("basis")
.x(function (d, i) { return x(i); })
.y(function (d) { return y(d); });
d3.select('.line').attr('d', line(data));
Now I want to know the vertical height of the line at a given horizontal pixel position. The data
array has lesser data points than pixels and the displayed line is interpolated, so it is not straight-forward to deduce the height of the line at a given pixel just from the data
array.
Any hints?
Edited 19-Sep-2012 per comments with many thanks to nrabinowitz!
You will need to do some sort of search of the data returned by getPointAtLength
. (See https://developer.mozilla.org/en-US/docs/DOM/SVGPathElement.)
// Line
var line = d3.svg.line()
.interpolate("basis")
.x(function (d) { return i; })
.y(function(d, i) { return 100*Math.sin(i) + 100; });
// Append the path to the DOM
d3.select("svg#chart") //or whatever your SVG container is
.append("svg:path")
.attr("d", line([0,10,20,30,40,50,60,70,80,90,100]))
.attr("id", "myline");
// Get the coordinates
function findYatX(x, linePath) {
function getXY(len) {
var point = linePath.getPointAtLength(len);
return [point.x, point.y];
}
var curlen = 0;
while (getXY(curlen)[0] < x) { curlen += 0.01; }
return getXY(curlen);
}
console.log(findYatX(5, document.getElementById("myline")));
For me this returns [5.000403881072998, 140.6229248046875].
This search function, findYatX
, is far from efficient (runs in O(n) time), but illustrates the point.
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