[Therion] Handling of tape and backtape in survey data

[Bruce Mutton]

I just checked on my little experiment of some years ago, and I
misrepresented it.

> PocketTopo automatically detects backsights if they are taken immediately
after a foresight.  So the software handles the station naming, no user
intervention required.  
That much is true. You end up with something like:
1.4 splays
1.4 1.5 shot
1.4 1.5 shot
1.4 1.5 shot

1.5 1.4 shot # for back shots it will recognise 1 or more shots within
tolerance as 'back legs', so you can do as many as you want, I think
1.5 1.4 shot
1.5 1.4 shot

1.5 splays
1.5 1.6 shot etc

>While I processed the only survey I ever did this way with Therion...
Not true.  I did not bother parsing the data from PocketTopo, as the passage
ends were too far apart to consider digging, and so no point to mapping with
Therion (we already have an older map).

Never the less, I am almost curious to see what TopParser and Therion does
with it.  Lots of loops and doubled survey length I expect.  Maybe I will
process it one day.

Tarquin
You mention that SexyTopo deals with this by treating the backsight as a
splay.  Does it detect and label this splay as a backleg if it is within
tolerance for the previous leg?  I think it should (similarly to
PocketTopo).  While I don't tend to use backsights as a rule, there is that
1 in 100 occasion where I do consider it, and I expect that the field
software should automatically detect this and number the shot/leg
accordingly.  In a generic sense, rigorous foresight/<move to next
station>/backsight/splay is a valid survey protocol (along with variations
of that).

Bruce