问题描述
我正在使用CV2从图像中查找轮廓，然后使用Shapely将其转换为多边形.我目前陷入困境，因为当我尝试将一个轮廓数组从Shapely放入Polygon()时，它将引发未指定的错误.
I am using CV2 to find contours from an image and then converting them into polygons using Shapely. I am currently stuck because when I try putting one of the contour arrays into Polygon() from Shapely it throws an unspecified error.
我已经仔细检查了是否导入了我需要的所有内容，以及当我手动输入数组坐标点时创建Shapely多边形的工作原理.
I have double-checked that I imported everything I needed, and that creating a Shapely polygon works when I manually enter the array coordinate points.
这是代码中有问题的部分:
Here is the problematic section of the code:
contours, hierarchy = cv2.findContours(thresh, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_SIMPLE)
testcontour = contours[1]
ply = Polygon(testcontour)
轮廓列表如下:
contours = [np.array([[[700, 700]],
[[700, 899]],
[[899, 899]],
[[899, 700]]]),
np.array([[[774, 775]],
[[775, 774]],
[[824, 774]],
[[825, 775]],
[[825, 824]],
[[824, 825]],
[[775, 825]],
[[774, 824]]]),
np.array([[[200, 200]],
[[200, 399]],
[[399, 399]],
[[399, 200]]]),
np.array([[[274, 275]],
[[275, 274]],
[[324, 274]],
[[325, 275]],
[[325, 324]],
[[324, 325]],
[[275, 325]],
[[274, 324]]])]
我得到的错误是:
---------------------------------------------------------------------------
AssertionError Traceback (most recent call last)
<ipython-input-65-4124f49b42e1> in <module>
----> 1 ply = Polygon(testcontour)
~\AppData\Local\Continuum\anaconda3\envs\geocomp\lib\site-packages\shapely\geometry\polygon.py in __init__(self, shell, holes)
238
239 if shell is not None:
--> 240 ret = geos_polygon_from_py(shell, holes)
241 if ret is not None:
242 self._geom, self._ndim = ret
~\AppData\Local\Continuum\anaconda3\envs\geocomp\lib\site-packages\shapely\geometry\polygon.py in geos_polygon_from_py(shell, holes)
492
493 if shell is not None:
--> 494 ret = geos_linearring_from_py(shell)
495 if ret is None:
496 return None
~\AppData\Local\Continuum\anaconda3\envs\geocomp\lib\site-packages\shapely\speedups\_speedups.pyx in shapely.speedups._speedups.geos_linearring_from_py()
AssertionError:
推荐答案
问题是由于某些原因cv2.findContours将每个轮廓作为具有一个冗余尺寸的3D NumPy数组返回:
The problem is that for some reason cv2.findContours returns each contour as a 3D NumPy array with one redundant dimension:
>>> contours[1]
array([[[774, 775]],
[[775, 774]],
[[824, 774]],
[[825, 775]],
[[825, 824]],
[[824, 825]],
[[775, 825]],
[[774, 824]]])
，但是Shapely希望采用这种形式的2D数组(请参阅文档):
but Shapely expects a 2D array in this form (see the docs):
array([[774, 775],
[775, 774],
[824, 774],
[825, 775],
[825, 824],
[824, 825],
[775, 825],
[774, 824]])
因此，我们可以做的是使用 删除多余的尺寸，并使用结果获取多边形:
So, what we can do is to use np.squeeze to remove that redundant dimension, and use the result to obtain our polygon:
import numpy as np
from shapely.geometry import Polygon
contour = np.squeeze(contours[1])
polygon = Polygon(contour)
print(polygon.wkt)
# POLYGON ((774 775, 775 774, 824 774, 825 775, 825 824, 824 825, 775 825, 774 824, 774 775))
如果要一次转换所有轮廓，我会这样做:
In case if you want to convert all of the contours at once, I would do it like this:
contours = map(np.squeeze, contours) # removing redundant dimensions
polygons = map(Polygon, contours) # converting to Polygons
multipolygon = MultiPolygon(polygons) # putting it all together in a MultiPolygon
生成的multipolygon将如下所示:
要从此处获取第二个多边形，您只需编写:
And to get the second polygon from here you would just write:
my_polygon = multipolygon[1]
print(my_polygon.wkt)
# POLYGON ((774 775, 775 774, 824 774, 825 775, 825 824, 824 825, 775 825, 774 824, 774 775))
这篇关于如何将从cv2.findContours获得的NumPy数组转换为Shapely多边形?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！