[Therion] Build a map with all centerline and partial walls

[Bill Gee]

I am looking at this entry in the Wiki:

https://therion.speleo.sk/wiki/tips#showing_centreline_for_parts_of_a_cave_and_passage_walls_for_others

My understanding it that this requires making two sets of centerline 
data, then creating a survey for each set.  One of the data sets is for 
that part of the cave which has walls/scraps and the other is for the 
remainder of the cave.

The thconfig file is set up with only one survey/endsurvey section.  I 
think this also would have to change into two sections.

Is this correct?

The cave I want to do this for has all centerline data in one big file. 
It would be a huge pain to separate that into two files.  Even more of a 
pain would be moving the data as sketching is completed.

Thanks!
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Bill Gee