def calculate_mean_r(imp, ring_rois, centres):
"""calculate the average distance of the cell surface from the vessel axis"""
w = imp.getWidth()
h = imp.getHeight()
rp = FloatProcessor(w, h)
rpix = rp.getPixels()
for lidx, (roi, centre) in enumerate(zip(ring_rois, centres)):
for thetaidx, (x, y) in enumerate(
zip(roi.getPolygon().xpoints,
roi.getPolygon().xpoints)):
rpix[lidx * w + thetaidx] = math.sqrt((x - centre[0])**2 +
(y - centre[1])**2)
rimp = ImagePlus("Radii", rp)
IJ.setAutoThreshold(rimp, "Intermodes light")
bp = rimp.createThresholdMask()
bp.dilate()
bp.erode()
mask_imp = ImagePlus("Mask", bp)
IJ.run(mask_imp, "Create Selection", "")
roi = mask_imp.getRoi()
rimp.setRoi(roi)
mean_r = rimp.getStatistics().mean
rimp.close()
mask_imp.close()
return mean_r
