[Therion] Handling of tape and backtape in survey data

[Bill Gee]

Hello everyone - 

I have a holiday question for the group.  We have for years done our survey shots both directions, obtaining a forward and backward reading for both compass and inclinometer.  The two readings are averaged by Survex and Therion in an effort to reduce errors.  The tape reading, however, has only been a single number.

Now that the use of DistoX2 devices is becoming common, it is easy to get a distance measurement both forward and backward.  I have been ignoring the backward distance reading in the field.  It does not get into my notes.  I might need to change that practice.

I looked at the Survex manual yesterday and see that it supports both TAPE and BACKTAPE (also called LENGTH and BACKLENGTH) in the survey data.  That brings up two questions:

1) Does Therion also recognize the BACKTAPE data type?

2) What does Survex do if both TAPE and BACKTAPE are given?  Does it average the two readings?  Does Therion do the same thing?

I understand that Therion will use Survex to reduce the centerline data - if Survex is installed.  In case Survex is NOT installed, then Therion reduces the centerline itself.  As a result they might handle this situation differently.

As I write this, another related question occurred to me.  When either Therion or Survex averages a forward and backward reading, how many significant digits does it carry in the calculation?  Can the significant digits be changed?

And the same question applies to loop closure calculations.  How many significant digits are carried through the calculations?

Thanks!
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Bill Gee