[Therion] Showing centreline for whole cave

[John Pybus]

Hi,

We're in the process of trying to draw up an extended elevation of a 
complicated part of one cave.  It would be very useful to see the 
centreline plotted for the whole cave.

I've added the metapost code from 
http://therion.speleo.sk/wiki/doku.php?id=metapost and it plots the 
whole line rather than just the ends (though it is only showing for half 
of the cave).  I've tried adding thee names of surveys which are not in 
the scraps to the map, but no centreline is shown.

Does anyone have any advise?  Is there a way to just get all the 
centreline plotted?

Thanks,
John