blocks|key|1289348|text|下面是一个函数，它在x坐标指定的<path>+(二进制搜索)上找到一个点：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|1289349|注记：路径在X上应该是单调的(在路径上，不能是2点，且x是相同的)|1289350|​|1289351|const+findPointAt+=+(path,+x)+=>+{
++let+from+=+0;
++let+to+=+path.getTotalLength();
++let+current+=+(from+%2B+to)+/+2;
++let+point+=+path.getPointAtLength(current);
++
++while+(Math.abs(point.x+-+x)+>+0.5)+{
++++if+(point.x+<+x)
++++++from+=+current;
++++else
++++++to+=+current;
++++current+=+(from+%2B+to)+/+2;
++++point+=+path.getPointAtLength(current);
++}
++return+point;
}


const+path+=+d3.select('path').node();

for+(let+x+=+0;+x+<=+200;+x+%2B=+50)+{
++const+pos+=+findPointAt(path,+x);
++console.log(pos);
++d3.select('svg').append('circle')
++++.attr('cx',+pos.x)
++++.attr('cy',+pos.y)
++++.attr('r',+3)
}|code-block|syntax|javascript|1289352|svg+{
++border:+1px+solid+gray;
}

path+{
++fill:+none;
++stroke:+blue;
}

circle+{
++fill:+red;
}|1289353|<script+src="https://cdnjs.cloudflare.com/ajax/libs/d3/5.7.0/d3.min.js"></script>

<svg+width="200"+height="150">
++<path+d="M+0,10+Q+40,0+90,80+C+120,120+150,70+220,20"+/>+
</svg>|1289354|1289355|entityMap^0|A|1|G|6|0|0|2|K|D|0|0|1|0|0|0|0|0|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]]|E|@]|F|$]]|$1|I|3|J|5|6|7|16|8|@$9|17|A|18|B|C]]|E|@]|F|$]]|$1|K|3|L|5|M|7|19|8|@]|E|@]|F|$N|O]]|$1|P|3|Q|5|M|7|1A|8|@]|E|@]|F|$N|O]]|$1|R|3|S|5|M|7|1B|8|@]|E|@]|F|$N|O]]|$1|T|3|J|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|E|@]|F|$]]|$1|U|3|-4|5|6|7|1F|8|@]|E|@]|F|$]]]|V|$]]

<p>Here is a function that finds a point with specified <strong>x</strong> coordinate on a <code>&lt;path&gt;</code> (kind of binary search):</p>
<p><strong>Note</strong>: The path should be <em>monotonic</em> on X (there <strong>must not</strong> be 2 points with the same x on the path)</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const findPointAt = (path, x) =&gt; {
  let from = 0;
  let to = path.getTotalLength();
  let current = (from + to) / 2;
  let point = path.getPointAtLength(current);
  
  while (Math.abs(point.x - x) &gt; 0.5) {
    if (point.x &lt; x)
      from = current;
    else
      to = current;
    current = (from + to) / 2;
    point = path.getPointAtLength(current);
  }
  return point;
}


const path = d3.select('path').node();

for (let x = 0; x &lt;= 200; x += 50) {
  const pos = findPointAt(path, x);
  console.log(pos);
  d3.select('svg').append('circle')
    .attr('cx', pos.x)
    .attr('cy', pos.y)
    .attr('r', 3)
}</code></pre>
<pre class="snippet-code-css lang-css prettyprint-override"><code>svg {
  border: 1px solid gray;
}

path {
  fill: none;
  stroke: blue;
}

circle {
  fill: red;
}</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://cdnjs.cloudflare.com/ajax/libs/d3/5.7.0/d3.min.js"&gt;&lt;/script&gt;

&lt;svg width="200" height="150"&gt;
  &lt;path d="M 0,10 Q 40,0 90,80 C 120,120 150,70 220,20" /&gt; 
&lt;/svg&gt;</code></pre>
</div>
</div>
</p>


blocks|key|235700|text|这真的是this的翻版，但是我添加了一个片段，因为这个帖子已经有好几年的历史了。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|235701|​|235702|const+margin+=+30;
const+width+=+400;+
const+height+=+180;
const+chartWidth+=+width+-+(margin+*+2);
const+chartHeight+=+height+-+(margin+*+2);

const+data+=+Array.from({length:+10},+(v,+i)+=>+{
++return+{
++++index:+i,
++++value:+Math.floor(Math.random()+*+20)+%2B+4
++}
});

const+svg+=+d3.select("#viz")
++.append("svg")
++.attr("width",+width)
++.attr("height",+height);
++
const+xScale+=+d3.scaleLinear()
++.domain(d3.extent(data,+d+=>+d.index))
++.range([0,+chartWidth]);
++
svg.append("g")
++.attr("class",+"x-axis")
++.attr("transform",+`translate(${margin},${height+-+margin})`)
++.call(d3.axisBottom(xScale));
++
const+yScale+=+d3.scaleLinear()
++.domain(d3.extent(data,+d+=>+d.value))
++.range([chartHeight,+0]);
++
svg.append("g")
++.attr("class",+"y-axis")
++.attr("transform",+`translate(${margin},${margin})`)
++.call(d3.axisLeft(yScale));
++++
const+line+=+d3.line()
++.x(d+=>+xScale(d.index))
++.y(d+=>+yScale(d.value))
++.curve(d3.curveCatmullRom);

const+series+=+svg.append("g")
++.attr("transform",+`translate(${margin},${margin})`)
++.append("path")
++.attr("d",+line(data))
++.attr("fill",+"transparent")
++.attr("stroke-width",+2)
++.attr("stroke",+"orange");

const+findYFromXLinearTime+=+(x,+line)+=>+{
++const+getXYAtLength+=+len+=>+{
++++const+pt+=+line.getPointAtLength(len);
++++return+{x:+pt.x,+y:+pt.y};
++}
++let+l+=+0;
++while+(getXYAtLength(l).x+<+x)+l%2B=0.01;
++return+getXYAtLength(l).y;
}

const+findYFromXLogTime+=+(x,+line)+=>+{
++const+error+=+0.01;
++const+iterMax+=+50;
++let+iter+=+0;
++let+start+=+0;
++let+end+=+line.getTotalLength();
++let+point+=+line.getPointAtLength((end+%2B+start)+/+2);
++while+(x+<+point.x+-+error+%7C%7C+x+>+point.x+%2B+error)+{
++++//+update+middle
++++point+=+line.getPointAtLength((end+%2B+start)+/+2);
++++//+test
++++x+<+point.x+?+end+=+(start+%2B+end)+/+2+:+start+=+(start+%2B+end+)+/+2;
++++//+update+iteration
++++if+(iterMax+<+%2B%2B+iter)+break;
++}
++return+point.y;
}

d3.select("#findY")
++.on("click",+evt+=>+{
++++const+x+=+document.getElementById("someX").value;
++++const+y+=+findYFromXLogTime(xScale(x),+series.node());
++++svg.append("circle")
++++++.attr("cx",+xScale(x)+%2B+margin)
++++++.attr("cy",+y+%2B+margin)
++++++.attr("r",+4)
++++++.attr("fill",+"red")
++++++.attr("stroke",+"black")
++});|code-block|syntax|javascript|235703|<script+src="https://cdnjs.cloudflare.com/ajax/libs/d3/6.7.0/d3.min.js"></script>
<input+id="someX"+type="number">
<button+id="findY"+type="button">find+Y</button>
<div+id="viz"></div>|235704|235705|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/11503151/in-d3-how-to-get-the-interpolated-line-data-from-a-svg-line^0|4|4|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|6|7|Z|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|10|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|M|3|E|5|6|7|12|8|@]|9|@]|C|$]]|$1|N|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|O|$P|$5|Q|R|S|C|$T|U]]]]

<p>It's really a duplicate of <a href="https://stackoverflow.com/questions/11503151/in-d3-how-to-get-the-interpolated-line-data-from-a-svg-line">this</a> but I added a snippet as the post is several years old ...</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const margin = 30;
const width = 400; 
const height = 180;
const chartWidth = width - (margin * 2);
const chartHeight = height - (margin * 2);

const data = Array.from({length: 10}, (v, i) =&gt; {
  return {
    index: i,
    value: Math.floor(Math.random() * 20) + 4
  }
});

const svg = d3.select("#viz")
  .append("svg")
  .attr("width", width)
  .attr("height", height);
  
const xScale = d3.scaleLinear()
  .domain(d3.extent(data, d =&gt; d.index))
  .range([0, chartWidth]);
  
svg.append("g")
  .attr("class", "x-axis")
  .attr("transform", `translate(${margin},${height - margin})`)
  .call(d3.axisBottom(xScale));
  
const yScale = d3.scaleLinear()
  .domain(d3.extent(data, d =&gt; d.value))
  .range([chartHeight, 0]);
  
svg.append("g")
  .attr("class", "y-axis")
  .attr("transform", `translate(${margin},${margin})`)
  .call(d3.axisLeft(yScale));
    
const line = d3.line()
  .x(d =&gt; xScale(d.index))
  .y(d =&gt; yScale(d.value))
  .curve(d3.curveCatmullRom);

const series = svg.append("g")
  .attr("transform", `translate(${margin},${margin})`)
  .append("path")
  .attr("d", line(data))
  .attr("fill", "transparent")
  .attr("stroke-width", 2)
  .attr("stroke", "orange");

const findYFromXLinearTime = (x, line) =&gt; {
  const getXYAtLength = len =&gt; {
    const pt = line.getPointAtLength(len);
    return {x: pt.x, y: pt.y};
  }
  let l = 0;
  while (getXYAtLength(l).x &lt; x) l+=0.01;
  return getXYAtLength(l).y;
}

const findYFromXLogTime = (x, line) =&gt; {
  const error = 0.01;
  const iterMax = 50;
  let iter = 0;
  let start = 0;
  let end = line.getTotalLength();
  let point = line.getPointAtLength((end + start) / 2);
  while (x &lt; point.x - error || x &gt; point.x + error) {
    // update middle
    point = line.getPointAtLength((end + start) / 2);
    // test
    x &lt; point.x ? end = (start + end) / 2 : start = (start + end ) / 2;
    // update iteration
    if (iterMax &lt; ++ iter) break;
  }
  return point.y;
}

d3.select("#findY")
  .on("click", evt =&gt; {
    const x = document.getElementById("someX").value;
    const y = findYFromXLogTime(xScale(x), series.node());
    svg.append("circle")
      .attr("cx", xScale(x) + margin)
      .attr("cy", y + margin)
      .attr("r", 4)
      .attr("fill", "red")
      .attr("stroke", "black")
  });</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://cdnjs.cloudflare.com/ajax/libs/d3/6.7.0/d3.min.js"&gt;&lt;/script&gt;
&lt;input id="someX" type="number"&gt;
&lt;button id="findY" type="button"&gt;find Y&lt;/button&gt;
&lt;div id="viz"&gt;&lt;/div&gt;</code></pre>
</div>
</div>
</p>


<p>I use d3js to draw a smooth curve. Then, I want to draw a point on the curve, but the point is random and I only have x value. I want get the function expression and get the y value with the x value. Is there any method to get the y value?</p>
<pre><code>const line = d3.line()
  .x(d =&gt; xScale(new Date(d.name)))
  .y(d =&gt; yScale(d.value1))
  .curve(d3.curveCatmullRom);
const series = svg.append('g')
  .attr('transform', `translate(${grid.left},${grid.top})`)
  .append('path')
  .attr('d', line(data))
  .attr('fill', 'transparent')
  .attr('stroke-width', 2)
  .attr('stroke', 'orange');
</code></pre>
<p>My current chart:
<img src="https://i.stack.imgur.com/cnx0S.png" alt="the chart I draw current" /></p>


Find a point on an SVG path

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我用d3js画了一条平滑的曲线。然后，我想在曲线上画一个点，但是这个点是随机的，我只有x值。我要得到函数表达式，用x值得到y值。有什么方法可以得到y值吗？const line = d3.line()  .x(d => xScale(new Date(d.name)))  .y(d => yScale(d.value1)...

问在SVG路径上找到一个点
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问在SVG路径上找到一个点EN