Get directional elements in matrix

Question

Lets suppose that I have a point of interest in my matrix that is NxN. The point is located in the position ij. So, given the index ij, is there a simple way to get the line elements passing trough ij and to the origin (that is located in the middle of the matrix) ?

I am using torch and I though that using torch.diag would be a first start but acttualy this function does not pass in the middle of the matrix.

def directionalK(kx,ky, indices):
    '''Function that provides the K values at a given direction dictated by the indices'''
    kx_grid,ky_grid = torch.meshgrid(kx,kx, indexing='ij')
    k_grid = torch.sqrt(kx_grid**2 + ky_grid**2) 
    k_grid[...,:len(k_grid)//2] *=-1 
    y,x = indices
    diag = x - len(k_grid)//2

Answer 1

I think you could solve this using the skimage.draw.line method where you input the starting (i,j) and ending (0,0) coordinates and it calculates the indices belonging to the line which you can use for indexing.

Worked example:

from skimage.draw import line
import numpy as np
import matplotlib.pyplot as plt
arr = np.zeros((100, 100))
i, j = 10, 80
origin = 50, 50
rr, cc = line(*origin, i, j)
arr[rr, cc] = 1
plt.imshow(arr, cmap='gray', interpolation='nearest')

Or if you want the line to continue:

arr = np.zeros((100, 100))
rr, cc = line(i, j, 2*origin[0]-i, 2*origin[1]-j)
arr[rr, cc] = 2
plt.imshow(arr, cmap='gray', interpolation='nearest')