Python：高效地使用形状测量区域属性的方法

Question

First of all, I apologize to post this easy question. I have a polygon

from shapely.geometry import Polygon

polygon = Polygon([(560023.4495758876400000 6362057.3904932579000000),(560023.4495758876400000 6362060.3904932579000000),(560024.4495758876400000 6362063.3904932579000000),(560026.9495758876400000 6362068.3904932579000000),(560028.4495758876400000 6362069.8904932579000000),(560034.9495758876400000 6362071.8904932579000000),(560036.4495758876400000 6362071.8904932579000000),(560037.4495758876400000 6362070.3904932579000000),(560037.4495758876400000 6362064.8904932579000000),(560036.4495758876400000 6362063.3904932579000000),(560034.9495758876400000 6362061.3904932579000000),(560026.9495758876400000 6362057.8904932579000000),(560025.4495758876400000 6362057.3904932579000000),(560023.4495758876400000 6362057.3904932579000000)])

My goal is compute the minor and the major axis of this polygon, following the Figure example:

I find this example in scikit-image but before to use a second module I wish to ask if there is in shapely module a method to calculate these indices.

thanks in advance

Answer 1

This question is a bit old but I ran into this myself recently, here's what I did:

from shapely.geometry import Polygon, LineString

polygon =  Polygon([(560023.4495758876400000, 6362057.3904932579000000),(560023.4495758876400000, 6362060.3904932579000000),(560024.4495758876400000, 6362063.3904932579000000),(560026.9495758876400000, 6362068.3904932579000000),(560028.4495758876400000, 6362069.8904932579000000),(560034.9495758876400000, 6362071.8904932579000000),(560036.4495758876400000, 6362071.8904932579000000),(560037.4495758876400000, 6362070.3904932579000000),(560037.4495758876400000, 6362064.8904932579000000),(560036.4495758876400000, 6362063.3904932579000000),(560034.9495758876400000, 6362061.3904932579000000),(560026.9495758876400000, 6362057.8904932579000000),(560025.4495758876400000, 6362057.3904932579000000),(560023.4495758876400000, 6362057.3904932579000000)])

# get the minimum bounding rectangle and zip coordinates into a list of point-tuples
mbr_points = list(zip(*polygon.minimum_rotated_rectangle.exterior.coords.xy))

# calculate the length of each side of the minimum bounding rectangle
mbr_lengths = [LineString((mbr_points[i], mbr_points[i+1])).length for i in range(len(mbr_points) - 1)]

# get major/minor axis measurements
minor_axis = min(mbr_lengths)
major_axis = max(mbr_lengths)

Shapely makes it easy to compute the mbr via minimum_rotated_rectangle , but it doesn't appear that the opposite sides are of exact equal length. Because of this, the above calculates the length of each side, then takes the min/max.

Answer 2

First calculate the Minimum Bounding Rectangle of the polygon - see the process described in How to find the minimum-area-rectangle for given points? , except you will start with the convex hull. In Shapely, use the .convex_hull() method to calculate the convex hull of your polygon.

Then once you have the MBR, you can find the major/minor axes.