Numpy中rot90函数实现矩阵旋转

Posted 2021-03-09 ratels

从NumPy的官方完整查到rot90函数语法格式如下：

rot90(m, k=1, axes=(0, 1)

m是要旋转的数组(矩阵)，k是旋转的次数，默认旋转1次，那是顺时针还是逆时针呢？正数表示逆时针，而k为负数时则是对数组进行顺时针方向的旋转。axes是由坐标轴定义的平面，旋转轴垂直于该平面，坐标轴必须不同，用于三维矩阵的旋转。

import numpy as np
mat = np.array([[1,3,5],
                [2,4,6],
                [7,8,9]
                ])
print mat, "# orignal"
mat90 = np.rot90(mat, 1)
print mat90, "# rorate 90 <left> anti-clockwise"
mat90 = np.rot90(mat, -1)
print mat90, "# rorate 90 <right> clockwise"
mat180 = np.rot90(mat, 2)
print mat180, "# rorate 180 <left> anti-clockwise"
mat270 = np.rot90(mat, 3)
print mat270, "# rorate 270 <left> anti-clockwise"

执行结果：

[[1 3 5]
 [2 4 6]
 [7 8 9]] # orignal
[[5 6 9]
 [3 4 8]
 [1 2 7]] # rorate 90 <left> anti-clockwise
[[7 2 1]
 [8 4 3]
 [9 6 5]] # rorate 90 <right> clockwise
[[9 8 7]
 [6 4 2]
 [5 3 1]] # rorate 180 <left> anti-clockwise
[[7 2 1]
 [8 4 3]
 [9 6 5]] # rorate 270 <left> anti-clockwise

三维矩阵围绕Z轴旋转：

import  numpy as np

if __name__ == ‘__main__‘:
    weights = np.array(
        [[[-1, 1, 0],
          [0, 1, 0],
          [0, 1, 1]],
         [[-1, -1, 0],
          [0, 0, 0],
          [0, -1, 0]],
         [[0, 0, -1],
          [0, 1, 0],
          [1, -1, -1]]], dtype=np.float64)
    flipped_weights = np.rot90(weights, 2 , (1,2))
    print(flipped_weights)

执行结果：

[[[ 1.  1.  0.]
  [ 0.  1.  0.]
  [ 0.  1. -1.]]
 [[ 0. -1.  0.]
  [ 0.  0.  0.]
  [ 0. -1. -1.]]
 [[-1. -1.  1.]
  [ 0.  1.  0.]
  [-1.  0.  0.]]]

 

参考：

http://liao.cpython.org/numpy13/

https://blog.csdn.net/weixin_39506322/article/details/89463286