Creating a path from the center points of a selection?

[mholder]

Ok got it thanks!

I tried this: 
- select the black line with the Fuzzy Selection Tool     (ok)
gimp menu :
- Select / To Path  (ok)
- Select / None     (ok)
- on path, right click : 
  - Tools / Cropping and Slicing / Crop path by rectangle  (error, then I use canvas option)
  - Edit / Break path apart   (ok)
  - Tools / Generate intermediate paths  (3)    (does nothing)

So what am I doing wrong here?  I can already think of many uses for this if I can get it to work.