如何从图中提取点？

Question

我有个问题.

我使用Matplotlib绘制了一个图形,如下所示:

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()

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

Answer 1

plot()返回一个有用的对象:[<matplotlib.lines.Line2D object at 0x38c9910>]
从中我们可以得到x轴和y轴值:

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

然后我们可以得到一个宽度值的索引:

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]),)

和相应的高度:

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

要检查我们可以使用get_xydata():

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