Find tunnel 'center line'?

Question

I have some map files consisting of \'polylines\' (each line is just a list of vertices) representing tunnels, and I want to try and find the tunnel \'center line\' (shown,

Answer 1

Well in Python using package skimage it is an easy task as follows.

import pylab as pl
from skimage import morphology as mp

tun = 1-pl.imread('tunnel.png')[...,0]        #your tunnel image
skl = mp.medial_axis(tun)                     #skeleton

pl.subplot(121)
pl.imshow(tun,cmap=pl.cm.gray)
pl.subplot(122)
pl.imshow(skl,cmap=pl.cm.gray)
pl.show()