Using grid lines but improving the corner detection

import numpy as np
import pyfits
import matplotlib.pyplot as plt
import skimage
from skimage.feature import blob_dog, blob_doh, blob_log, canny
from skimage.color import rgb2gray
from skimage.feature import corner_harris, corner_subpix, corner_peaks
from skimage.segmentation import slic
from skimage.filters import sobel
from scipy.signal import convolve2d
from scipy.ndimage import gaussian_filter
from skimage import measure
from scipy.optimize import curve_fit
import matplotlib.ticker as mtick

path = '/home/fatima/Desktop/solar_orbiter_project/codes/targets/distortion/'
path_paper = '/home/fatima/Desktop/solar_orbiter_project/codes/notebooks/distortion/images_paper/'
#grid = pyfits.getdata(path+'solo_L0_0000015224_20170411T152003.fits')
grid = pyfits.getdata(path+'calibration_lines.fits')
dark = pyfits.getdata(path+'dark.fits')
#grid = grid/dark


#points = points[402:1813,52:1816] #circles
#grid = grid[135:1759,168:1792]

fig=plt.figure(figsize=(20,10))
ax1 = fig.add_subplot(121)
ax2 = fig.add_subplot(122)
ax1.imshow(dark)
ax2.imshow(grid)

<matplotlib.image.AxesImage at 0x7fe91ccbc910>

edge = sobel(grid)

#hdu = pyfits.PrimaryHDU(edge)
#hdu.writeto('edge.fits')

fig=plt.figure(figsize=(25,12))
plt.imshow(edge)

<matplotlib.image.AxesImage at 0x7fbebe4c5b50>