radial_profile: 'center' mode passes physical coordinates where pixel indices are expected #93

Problem

sigima.proc.image.radial_profile with center="center" passes the physical coordinates of the image center (ImageObj.xc, yc) to sigima.tools.image.get_radial_profile, which expects pixel indices (the centroid mode passes indices, and the x0/y0 parameters of the user mode are documented in pixels). The result is only correct for images with x0 = y0 = 0 and dx = dy = 1.

Reproduction (Gaussian peak at the center of an 11 × 11 image):

import numpy as np, sigima.objects as so, sigima.proc.image as sipi, sigima.params as sp
y, x = np.indices((11, 11)); data = np.exp(-((x - 5) ** 2 + (y - 5) ** 2) / 4.0)
for x0, dx in ((0.0, 1.0), (100.0, 1.0), (0.0, 0.1)):
    img = so.create_image("g", data.copy()); img.set_uniform_coords(dx, dx, x0, x0)
    s = sipi.radial_profile(img, sp.RadialProfileParam.create(center="center"))
    print(x0, dx, img.xc, len(s.y), np.nanmax(s.y))

The X axis of the profile (distances) is also in pixels whatever the calibration, and non-uniform coordinates are not taken into account.

Found while auditing the 1.4 contract versions (#87): radial_profile is now at contract version 2 because xc/yc changed; this issue is about its pre-existing mix of physical and pixel coordinates.

Expected

The center mode uses the pixel indices of the center of the pixel grid (or the whole function works in physical coordinates, consistently for the three modes and for the X axis of the profile).