获取图表值 [英] get chart value in point

问题描述

例如，我有2点的图表-0,0和10,10，图表类型为FastLine. 我想知道所选X值中图表中的Y值.

For example I have chart with 2 points - 0,0 and 10,10 and chart type is FastLine. I want to know what Y value will be in chart in choosen X value.

例如，当X为5时，我想知道Y为5.

For example when X is 5 I want to know that Y is 5.

我的图表更加复杂并且有很多点，我需要通过X获得Y值.

My charts more complicated and have tons of points, I need to get Y value through X.

我该怎么做?

推荐答案

问题归结为两个任务:

• 找到x值的相邻点
• 将它们的y值内插给定的x值.

如果x值确实在稳步增加，则应同时解决这两个问题:

If the x-values are indeed steadily increasing this should solve both:

double interpolatedY(Series s, double xval)
{
    DataPoint pPrev = s.Points.Last(x => x.XValue <= xval);
    DataPoint pNext = s.Points.First(x => x.XValue >= xval);

    if (pPrev == pNext) return pPrev.YValues[0];

    return pPrev.YValues[0] + (pNext.YValues[0] - pPrev.YValues[0])
        * (xval  - pPrev.XValue)/ (pNext.XValue - pPrev.XValue); 
}

它使用Linq查找上一个和下一个数据点，然后使用简单的数学查找插值.

It uses Linq to find the previous and next datapoint and then uses simple math to find the interpolated value.

请注意，大多数检查都被省略了！

Note that most checks are omitted!

在这里，我添加了一个相同的点序列，并添加了第三个序列以添加插值:

Here I have added an identical point series and a third one to add the interpolated values:

要在图表像素和值之间转换，请使用Axis函数ValueToPixelPosition和PixelPositionToValue，顺便说一句.

To convert between chart pixels and values there are Axis functions ValueToPixelPosition and PixelPositionToValue, btw.

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