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获取旋转补丁(矩形)matplotlib 的坐标

分类: 技术问答 • 2022-06-10 12:18:43
问题描述：

我想实现以下目标:

  • 1) 获取旋转面片的坐标
  • 2)获取补丁的所有点(此处为矩形)
  • ** 我的印象是旋转的矩形在面之间没有 90 度.那只是可视化吗?

下面的我的代码段.但是，旋转的面片的坐标与原始面的坐标相同.如何实现1)和2)?

My snippet below. The coordinates of the rotated patch are the same as of the original though .. How to achieve 1) and 2) ? 

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.patches as patches
import matplotlib as mpl

from matplotlib.transforms import Affine2D

fig = plt.figure()
ax = fig.add_subplot(111)
angle = np.deg2rad(45)

r1 = patches.Rectangle((8,4), 5,3, fill=False, color="red", alpha=0.50)
r2 = patches.Rectangle((8,4), 5,3, fill=False, color="blue",  alpha=0.50)

trafo = mpl.transforms.Affine2D().rotate_around(8,4,angle) + ax.transData
r2.set_transform(trafo)

ax.add_patch(r1)
ax.add_patch(r2)

plt.xlim(0,15)
plt.ylim(0,15)

plt.grid(False)

plt.show()
print(r1.get_bbox())
print(r1.get_xy())
print(r2.get_bbox()) # why are they the same as for r1?
print(r2.get_xy())
#print(r1.get_all_points()) # how to achieve it?

答

矩形的坐标

Rectangle 是通过左下角(x，y)以及宽度和高度的坐标对定义的.要获取其角的坐标，您可以

Rectangle's coordinates

A Rectangle is defined through a coordinate pair of the lower left corner (x,y), and a width and height. To get the coordinates of its corners, you may

  • 从角落，宽度和高度计算它们

  • calculate them from the corner, width and height,

r1 = patches.Rectangle((8,4), 5,3)
ax.add_patch(r1)
coords = np.array([r1.get_xy(), [r1.get_x()+r1.get_width(), r1.get_y()],
                   [r1.get_x()+r1.get_width(), r1.get_y()+r1.get_height()],
                   [r1.get_x(), r1.get_y()+r1.get_height()]])
print(coords)

  • 从转换后的路径中获取它们，

  • get them from the transformed path,

    r1 = patches.Rectangle((8,4), 5,3)
ax.add_patch(r1)
coords = r1.get_patch_transform().transform(r1.get_path().vertices[:-1])
print(coords)

    • 在两种情况下，打印结果均为

    In both cases the printed result will be

    [[  8.   4.]
 [ 13.   4.]
 [ 13.   7.]
 [  8.   7.]]

    您还可以从矩形的边界框获得左下角和右上角的两个点(由于一个框本身是矩形)，

    You may also get the two points of the lower left and upper right corner from the rectangle's bounding box (due to a box being a Rectangle itself),

    r1 = patches.Rectangle((8,4), 5,3)
ax.add_patch(r1)
coords = r1.get_bbox().get_points()
print(coords)

    with将导致

    [[  8.   4.]
 [ 13.   7.]]

    变换后的矩形的坐标.

    现在，如果要变换矩形，则上述方法需要考虑到变换，以提供变换后的矩形的正确坐标.

    Transformed rectangle's coordinates.

    Now if you transform the rectangle, the above methods need to take the transform into account to provide the correct coordinates of the transformed rectangle.

    • 转换手动获取的坐标，

    • transform the manually obtained coordinates,

    r2 = patches.Rectangle((8,4), 5,3)

trafo = mpl.transforms.Affine2D().rotate_around(8,4,angle)
r2.set_transform(trafo + ax.transData)
ax.add_patch(r2)
coords = np.array([r2.get_xy(), [r2.get_x()+r2.get_width(), r2.get_y()],
 [r2.get_x()+r2.get_width(), r2.get_y()+r2.get_height()],
 [r2.get_x(), r2.get_y()+r2.get_height()]])
print(trafo.transform(coords))

  • 变换从路径获得的坐标

  • transform the coordinates obtained from the path

    r2 = patches.Rectangle((8,4), 5,3)

trafo = mpl.transforms.Affine2D().rotate_around(8,4,angle)
r2.set_transform(trafo + ax.transData)
ax.add_patch(r2)

coords = r2.get_patch_transform().transform(r2.get_path().vertices[:-1])
print(trafo.transform(coords))

    • 在这些情况下，打印的坐标将是

    In those cases, the printed coordinates will be 

    [[  8.           4.        ]
 [ 11.53553391   7.53553391]
 [  9.41421356   9.65685425]
 [  5.87867966   6.12132034]]

    或者，如果要从边界框中获取余项

    Or, in case of getting the coodinates from the bounding box

    coords = r2.get_bbox().get_points()
print(trafo.transform(coords))

    印刷品

    [[ 8.          4.        ]
 [ 9.41421356  9.65685425]]

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