如何从图中提取点? [英] How to extract points from a graph?

问题描述

我有一个问题.

我使用 Matplotlib 绘制了一个图形，如下所示:

from matplotlib import pyplot导入 numpy从 scipy.interpolate 导入样条宽度 = numpy.array([0, 30, 60, 90, 120, 150, 180])高度 = numpy.array([26, 38.5, 59.5, 82.5, 120.5, 182.5, 319.5])xnew = numpy.linspace(widths.min(),widths.max(),300)heights_smooth = 样条(宽度，高度，xnew)pyplot.plot(xnew,heights_smooth)pyplot.show()

现在我想使用宽度值作为参数来查询高度值.我似乎无法找到如何做到这一点.请帮忙！提前致谢！

解决方案

plot() 返回一个有用的对象:[]
从中我们可以得到 x 轴和 y 轴的值:

导入 matplotlib.pyplot 为 plt，numpy 为 np...line2d = plt.plot(xnew,heights_smooth)xvalues = line2d[0].get_xdata()yvalues = line2d[0].get_ydata()

然后我们可以得到宽度值之一的索引:

idx = np.where(xvalues==xvalues[-2]) # 这是 179.3979933110368# idx 是一个数组元组，其中包含找到值的索引# 在这种情况下 ->(数组([298])，)

和对应的高度:

yvalues[idx]# ->数组([315.53469])

我们可以使用get_xydata()来检查:

<预><代码>>>>xy = line2d[0].get_xydata()>>>xy[-2]数组([ 179.39799331, 315.53469 ])

I have a question.

I have plotted a graph using Matplotlib like this:

from matplotlib import pyplot
import numpy
from scipy.interpolate import spline

widths = numpy.array([0, 30, 60, 90, 120, 150, 180])
heights = numpy.array([26, 38.5, 59.5, 82.5, 120.5, 182.5, 319.5])

xnew = numpy.linspace(widths.min(),widths.max(),300)
heights_smooth = spline(widths,heights,xnew)

pyplot.plot(xnew,heights_smooth)
pyplot.show()

Now I want to query a height value using width value as an argument. I cannot seem to find how to do that. Please help! Thanks in advance!

解决方案

plot() returns a useful object: [<matplotlib.lines.Line2D object at 0x38c9910>]
From that we can get x- and y-axis values:

import matplotlib.pyplot as plt, numpy as np
...
line2d = plt.plot(xnew,heights_smooth)
xvalues = line2d[0].get_xdata()
yvalues = line2d[0].get_ydata()

Then we can get the index of one of the width values:

idx = np.where(xvalues==xvalues[-2]) # this is 179.3979933110368
# idx is a tuple of array(s) containing index where value was found
# in this case -> (array([298]),)

And the corresponding height:

yvalues[idx]
# -> array([ 315.53469])

To check we can use get_xydata():

>>> xy = line2d[0].get_xydata()
>>> xy[-2]
array([ 179.39799331,  315.53469   ])

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