在numpy数组中屏蔽圆形扇区

Question

我有一个代码将一个numpy数组切成一个圆圈.我希望仅从圆圈中恢复包含在特定角度范围内的值并掩盖数组.例如:屏蔽原始数组,其中(x,y)位置包含在圆圈的0到45度之间.

有这样做的pythonic方式吗？

这是我的(简化)原始代码:

import numpy as np
matrix = np.zeros((500,500))
x = 240
y = 280
radius = 10
mask=np.ogrid[x-radius:x+radius+1,y-radius:y+radius+1]
matrix[mask]

提前致谢

编辑:我省略了半径可以变化.

Answer 1

我会这样做,从笛卡儿坐标到极坐标转换,并为圆圈和你想要的角度范围构建布尔蒙版:

import numpy as np

def sector_mask(shape,centre,radius,angle_range):
    """
    Return a boolean mask for a circular sector. The start/stop angles in  
    `angle_range` should be given in clockwise order.
    """

    x,y = np.ogrid[:shape[0],:shape[1]]
    cx,cy = centre
    tmin,tmax = np.deg2rad(angle_range)

    # ensure stop angle > start angle
    if tmax < tmin:
            tmax += 2*np.pi

    # convert cartesian --> polar coordinates
    r2 = (x-cx)*(x-cx) + (y-cy)*(y-cy)
    theta = np.arctan2(x-cx,y-cy) - tmin

    # wrap angles between 0 and 2*pi
    theta %= (2*np.pi)

    # circular mask
    circmask = r2 <= radius*radius

    # angular mask
    anglemask = theta <= (tmax-tmin)

    return circmask*anglemask

例如:

from matplotlib import pyplot as pp
from scipy.misc import lena

matrix = lena()
mask = sector_mask(matrix.shape,(200,100),300,(0,50))
matrix[~mask] = 0
pp.imshow(matrix)
pp.show()