distance between concentric circle at various angles using opencv

Question

im using the below code to detect concentric circles and measure distance at various angles. outer circle matrix shape is zero and im getting error - valueerror: operands could not be broadcast together with shapes (0,) (2,). please help to solve the error . image attached for you reference

import cv2
import numpy as np
import shapely.geometry as shapgeo

# Read image, and binarize
img = cv2.imread('/Users/n/Opencv/New_OpenCv/image.jpeg', cv2.IMREAD_GRAYSCALE)
img = cv2.threshold(img, 128, 255, cv2.THRESH_BINARY)[1]

# Find (approximated) contours of inner and outer shape
cnts, hier = cv2.findContours(img, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)
outer = [cv2.approxPolyDP(cnts[0], 0.1, True)]
inner = [cv2.approxPolyDP(cnts[2], 0.1, True)]

# Just for visualization purposes: Draw contours of inner and outer shape
h, w = img.shape[:2]
vis = np.zeros((h, w, 3), np.uint8)
cv2.drawContours(vis, outer, -1, (255, 0, 0), 1)
cv2.drawContours(vis, inner, -1, (0, 0, 255), 1)

# Squeeze contours for further processing
outer = np.vstack(outer).squeeze()
inner = np.vstack(inner).squeeze()

# Calculate centroid of inner contour
M = cv2.moments(inner)
cx = int(M['m10'] / M['m00'])
cy = int(M['m01'] / M['m00'])

# Calculate maximum needed radius for later line intersections
r_max = np.min([cx, w - cx, cy, h - cy])

# Set up angles (in degrees)
angles = np.arange(0, 360, 4)

# Initialize distances
dists = np.zeros_like(angles)

# Prepare calculating the intersections using Shapely
poly_outer = shapgeo.asLineString(outer)
poly_inner = shapgeo.asLineString(inner)

# Iterate angles and calculate distances between inner and outer shape
for i, angle in enumerate(angles):

    # Convert angle from degrees to radians
    angle = angle / 180 * np.pi

    # Calculate end points of line from centroid in angle's direction
    x = np.cos(angle) * r_max + cx
    y = np.sin(angle) * r_max + cy
    points = [(cx, cy), (x, y)]

    # Calculate intersections using Shapely
    poly_line = shapgeo.LineString(points)
    insec_outer = np.array(poly_outer.intersection(poly_line))
    insec_inner = np.array(poly_inner.intersection(poly_line))

    # Calculate distance between intersections using L2 norm
    dists[i] = np.linalg.norm(insec_outer - insec_inner)

    # Just for visualization purposes: Draw lines for some examples
    if (i == 10) or (i == 40) or (i == 75):

        # Line from centroid to end points
        cv2.line(vis, (cx, cy), (int(x), int(y)), (128, 128, 128), 1)

        # Line between both shapes
        cv2.line(vis,
                 (int(insec_inner[0]), int(insec_inner[1])),
                 (int(insec_outer[0]), int(insec_outer[1])), (0, 255, 0), 2)

        # Distance
        cv2.putText(vis, str(dists[i]), (int(x), int(y)),
                    cv2.FONT_HERSHEY_COMPLEX, 0.75, (0, 255, 0), 2)

# Output angles and distances
print(np.vstack([angles, dists]).T)
print(poly_outer)
print(poly_inner)
print(poly_line)
print(insec_inner)
print(insec_outer)
# Just for visualization purposes: Output image
cv2.imshow('Output', vis)
cv2.waitKey(0)
cv2.destroyAllWindows()