在 matplotlib 中将数据坐标转换为轴坐标

Question

我正在尝试将数据点从数据坐标系转换为 matplotlib 中的轴坐标系。

import matplotlib.pyplot as plt


fig, ax = plt.subplots()
# this is in data coordinates
point = (1000, 1000)
# this takes us from the data coordinates to the display coordinates.
trans = ax.transData.transform(point)
print(trans)  # so far so good.
# this should take us from the display coordinates to the axes coordinates.
trans = ax.transAxes.inverted().transform(trans)
# the same but in one line
# trans = (ax.transData + ax.transAxes.inverted()).transform(point)
print(trans)  # why did it transform back to the data coordinates? it
# returns [1000, 1000], while I expected [0.5, 0.5]
ax.set_xlim(0, 2000)
ax.set_ylim(0, 2000)
ax.plot(*trans, 'o', transform=ax.transAxes)
# ax.plot(*point, 'o')
fig.show()

我阅读了我的代码所基于的 transformation tutorial and tried the solution presented in this answer，但它不起作用。我只是想不通为什么，这让我发疯。我确信有一个简单的解决方案，但我就是没看到。

Answer 1

好的，我发现了（明显的）问题。为了使转换工作，我需要在调用转换之前设置轴限制，我想这是有道理的。

import matplotlib.pyplot as plt


fig, ax = plt.subplots()
ax.set_xlim(0, 2000)
ax.set_ylim(0, 2000)
point = (1000, 1000)
trans = (ax.transData + ax.transAxes.inverted()).transform(point)
print(trans) 
ax.plot(*trans, 'o', transform=ax.transAxes)
# ax.plot(*point, 'o')
fig.show()

Answer 2

转换正在运行，只是当您开始时，默认轴限制为 0、1，并且它不会提前知道您打算更改限制：

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
# this is in data coordinates
point = (1000, 1000)
trans = ax.transData.transform(point)
trans = ax.transAxes.inverted().transform(trans)
print(ax.get_xlim(), trans)  

ax.set_xlim(0, 2000)
ax.set_ylim(0, 2000)
trans = ax.transData.transform(point)
trans = ax.transAxes.inverted().transform(trans)
print(ax.get_xlim(), trans)

产量：

(0.0, 1.0) [1000. 1000.]
(0.0, 2000.0) [0.5 0.5]

在 matplotlib 中将数据坐标转换为轴坐标

Convert from data coordinates to axes coordinates in matplotlib

python

transform

matplotlib