d3javascript，获取svg路径中两点之间的距离

Question

我有一组点，通过这些点我绘制了一条路径。

let path=svg.append("path").attr("id","path")
.data([points])
.attr("d", d3.line()
.curve(d3.curveCatmullRom));

我现在想得到点之间的路径距离，这样我就可以把它分成段。我试着增加距离，检查点(四舍五入到5(是否与初始点集的点匹配，从而在匹配时获得距离。然后我将这些点保存为列表。

这里，xyArray具有我向其附加d的点的列表以及列表seg。

function distanceBetween2Points(path, xyArray) {
let distance = 0;
xyArray.forEach(function(d,i)
{
let flag=1;
seg=[];
while(flag)
{let pt=path.getPointAtLength(distance);
if(round5(pt.x)==round5(d.x) && round5(pt.y)==round5(d.y))
{console.log("d",i);
d.d=distance;
d.seg=seg;
flag=0;
break;}
seg.push([pt.x,pt.y]);
distance++;}
return 0;
});
}

它有时有效(尽管不准确(，但有时无效，这取决于数据。有更好的方法来跑这段距离吗？

Answer 1

这是一个使用香草javascript而非d3的演示，但我希望您会发现它很有用。

函数getLengthForPoint(p,thePath)计算给定点p在路径上的距离。我正在设置一个变量let precision = 100;。根据路径的长度，您可能希望将此值更改为其他值。

还要记住，一条路径可以多次通过同一点。这可能很棘手，可能会给您带来错误。

正如你可能知道的，你会得到一个点的近似距离。在本例中，点p1 = {x:93.5,y:60}。计算长度处的点具有以下坐标：{x:93.94386291503906,y: 59.063079833984375}

// some points on the path
let p1 = {x:93.5,y:60}
let p2 = {x:165,y:106}
//the total length of the path
let pathLength = thePath.getTotalLength();
let precision = 100;
let division = pathLength / precision;
function getLengthForPoint(p,thePath){
let theRecord = pathLength;
let theSegment;
for (let i = 0; i < precision; i++) {
// get a point on the path for thia distance
let _p = thePath.getPointAtLength(i * division);
// get the distance between the new point _p and the point p
let theDistance = dist(_p, p);
if (theDistance < theRecord) {
// if the distance is smaller than the record set the new record
theRecord = theDistance; 
theSegment = i;
}
}
return(theSegment * division);
}
let theDistanceOnThePath = getLengthForPoint(p1,thePath);
//if you calculate the coords of a point at the calculated distance you'll see that is very near the point 
console.log(thePath.getPointAtLength(theDistanceOnThePath));
let theDistanceBetween2PointsOnThePath = getLengthForPoint(p2,thePath) - getLengthForPoint(p1,thePath);

// a helper function to measure the distance between 2 points
function dist(p1, p2) {
let dx = p2.x - p1.x;
let dy = p2.y - p1.y;
return Math.sqrt(dx * dx + dy * dy);
}

svg{border:solid}

<svg viewBox="0 10 340 120">
<path id="thePath" fill="none" stroke="black" d="M10, 24Q10,24,40,67Q70,110,93.5,60Q117,10,123.5,76Q130,142,165,106Q200,70,235,106.5Q270,143, 320,24"></path>
<circle cx="93.5" cy="60" r="2" fill="red"/>
<circle cx="165" cy="106" r="2" fill="red"/>
</svg>

要获得路径上2个点之间的距离，可以执行以下操作：

let theDistanceBetween2PointsOnThePath = getLengthForPoint(p2,thePath) - getLengthForPoint(p1,thePath);