使用 matplotlib 在对数刻度上居中注释

Question

我有以下不言自明的情况；请参阅下面粘贴的图和工作示例。我想知道如何在尺寸线的中间居中文本。import numpy as npimport matplotlib.pyplot as plt# Dimension linedef annotation_line(ax, xmin, xmax, y, text, ytext=0, linecolor='black', linewidth=1, fontsize=12):    ax.annotate('', xy=(xmin, y), xytext=(xmax, y), xycoords='data', textcoords='data', arrowprops={'arrowstyle': '|-|', 'color':linecolor, 'linewidth':linewidth})    ax.annotate('', xy=(xmin, y), xytext=(xmax, y), xycoords='data', textcoords='data', arrowprops={'arrowstyle': '<->', 'color':linecolor, 'linewidth':linewidth})    xcenter = xmin + (xmax - xmin) / 2    if ytext==0:        ytext = y + ( ax.get_ylim()[1] - ax.get_ylim()[0] ) / 20    ax.annotate(text, xy=(xcenter, ytext), ha='center', va='bottom', fontsize=fontsize)# Toy dataN = 8y = np.zeros(N)x1 = np.linspace(1, 1000, N, endpoint=True)fig, ax = plt.subplots(figsize=(10, 6))ax.plot(x1, y, 'o')annotation_line(ax=ax, text='TEXT 1', xmin=1, xmax=100, y=0.01, ytext=0, linewidth=1, linecolor='gray', fontsize=12)ax.set_xscale('log')

Answer 1

简单的解决方案是按照@JohanC 的建议进行操作并计算对数坐标的中点。

另一种解决方案是使用箭头的坐标来找到它的中点。然而，这种方法也有缺点。首先，您需要在中间步骤显式绘制图形，因为坐标仅在绘制时有效，其次，您需要在绘制注释之前设置对数比例。另一方面，无论轴的缩放如何，代码都可以工作

import numpy as np

import matplotlib.pyplot as plt

# Dimension line

def annotation_line(ax, xmin, xmax, y, text, ytext=0, linecolor='black', linewidth=1, fontsize=12):

    an = ax.annotate('', xy=(xmin, y), xytext=(xmax, y), xycoords='data', textcoords='data', arrowprops={'arrowstyle': '|-|', 'color':linecolor, 'linewidth':linewidth})

    ax.annotate('', xy=(xmin, y), xytext=(xmax, y), xycoords='data', textcoords='data', arrowprops={'arrowstyle': '<->', 'color':linecolor, 'linewidth':linewidth})

    ax.figure.canvas.draw() # draw to get actual coordinates

    p = an.arrow_patch.get_path().transformed(ax.transAxes.inverted())

    xmin, xmax = np.min(p.vertices[:,0]),np.max(p.vertices[:,0])

    xcenter = xmin+(xmax-xmin)/2

    if ytext==0:

        ytext = y + ( ax.get_ylim()[1] - ax.get_ylim()[0] ) / 20

    ax.annotate(text, xy=(xcenter, ytext), xycoords=('axes fraction','data'), ha='center', va='bottom', fontsize=fontsize)

    return an

# Toy data

N = 8

y = np.zeros(N)

x1 = np.linspace(1, 1000, N, endpoint=True)

fig, ax = plt.subplots(figsize=(10, 6))

ax.plot(x1, y, 'o')

ax.set_xscale('log') # must do before the call to annotation_line

an = annotation_line(ax=ax, text='TEXT 1', xmin=1, xmax=100, y=0.01, ytext=0, linewidth=1, linecolor='gray', fontsize=12)