python - 在图形上绘制椭圆并获取坐标_Python

Question

我正在研究 Python 2.7。我必须在图片上定义一些感兴趣区域 (AoI)。基本上，我试图在图片的特定部分上绘制一个椭圆(或更多)并获取其轮廓的坐标(x；y)。我想将这些坐标保存在文件中，以便稍后使用它们来查看我的数据是否在该区域内。

这是我的代码:

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.patches import Ellipse, Circle
from matplotlib.path import Path

# Get an example image

img = imread('sposa.png')

# Create a figure. Equal aspect so circles look circular
fig,ax = plt.subplots(1)
ax.set_aspect('equal')

# Show the image
ax.imshow(img)
ax.set_xlim(0,1600)
ax.set_ylim(0,1200)
# Now, loop through coord arrays, and create a circle at each x,y pair
ellipse = Ellipse((1000, 400), width=400, height=100, edgecolor='white',facecolor='none',linewidth=2)

ax.add_patch(ellipse)
path = ellipse.get_path()

# Show the image
plt.show()

当我运行代码时，我得到了这个(这正是我想要的):

但是，当我打印路径以检查它时，我得到以下输出，(我认为)它与椭圆完全相关。

Path(array([[ 0.        , -1.        ],
   [ 0.2652031 , -1.        ],
   [ 0.51957987, -0.89463369],
   [ 0.70710678, -0.70710678],
   [ 0.89463369, -0.51957987],
   [ 1.        , -0.2652031 ],
   [ 1.        ,  0.        ],
   [ 1.        ,  0.2652031 ],
   [ 0.89463369,  0.51957987],
   [ 0.70710678,  0.70710678],
   [ 0.51957987,  0.89463369],
   [ 0.2652031 ,  1.        ],
   [ 0.        ,  1.        ],
   [-0.2652031 ,  1.        ],
   [-0.51957987,  0.89463369],
   [-0.70710678,  0.70710678],
   [-0.89463369,  0.51957987],
   [-1.        ,  0.2652031 ],
   [-1.        ,  0.        ],
   [-1.        , -0.2652031 ],
   [-0.89463369, -0.51957987],
   [-0.70710678, -0.70710678],
   [-0.51957987, -0.89463369],
   [-0.2652031 , -1.        ],
   [ 0.        , -1.        ],
   [ 0.        , -1.        ]]), array([ 1,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,
    4,  4,  4,  4,  4,  4,  4,  4, 79], dtype=uint8))

但是，我需要一个椭圆相对于图片像素 (1600 X 1200) 的坐标列表。我可能使用了错误的函数，或者图片和椭圆之间存在不匹配的内容。

我应该得到这样的东西(这是之前实验的一个例子):

[ Path(array([[ 1599.        ,   868.86791294],
   [ 1598.        ,   868.87197971],
   [ 1597.        ,   868.8801087 ],
   ..., 
   [ 1597.        ,   675.30378536],
   [ 1598.        ,   675.31373204],
   [ 1599.        ,   675.31870792]]), None)]
665 

有人可以帮助我吗？ 先感谢您，

Answer 1

您应该使用Ellipse.get_path().vertices，但它不在正确的坐标系中。要对其进行转换，请对其应用ellipse.get_patch_transform().transform。请参阅下面的工作示例

import matplotlib.pyplot as plt
from matplotlib.patches import Ellipse
from matplotlib.path import Path
from matplotlib.patches import PathPatch

img = plt.imread("image.jpg")

fig, ax = plt.subplots(1)
ax.set_aspect('equal')

ax.imshow(img)

# Create the base ellipse
ellipse = Ellipse((300, 300), width=400, height=100,
                  edgecolor='white', facecolor='none', linewidth=2)

# Get the path
path = ellipse.get_path()
# Get the list of path vertices
vertices = path.vertices.copy()
# Transform the vertices so that they have the correct coordinates
vertices = ellipse.get_patch_transform().transform(vertices)

# You can then save the vertices array to a file: csv, pickle... It's up to you

plt.show()