[Therion] Handling of tape and backtape in survey data

[Andrew Atkinson]

On 27/12/2021 19:41, Tarquin Wilton-Jones via Therion wrote:
>> But because DistoX is an electronic device it is only way to be sure it
>> works properly. The same as check, if three (four) readings for
>> surveying leg with rotation around the longitudinal axe of DistoX are in
>> tolerance interval.
> Oh very true. This is one of the checks I recommend performing
> occasionally to test calibration (or every leg when working around
> scaffolding or magnetic rocks). Create legs with one reading flat, one
> rotated 90 degrees longitudinally, another reading flat or in any other
> orientation. Then validate with a splay back to the previous station.

I think, but have no proof, that if you rotate the distoX it is probably 
better than a manual backsight. pockettopo records the rotation, and I 
have this in the therion file. People surveying with me know I check 
that they rotate at least every 5 stations and i relity they rotate most 
station. All the times I've been with people doing backsights (mainly US 
cavers) all it seems to stop is blunders, if they don't get a reading 
that is within their personal tolerance they do it all again. The real 
question is how much are they doing expectation bias? I cannot really 
comment further as I have too little experience of this.


On 27/12/2021 19:36, Bill Gee wrote:
>> I remember seeing a presentation at a recent NSS Convention (2020, maybe?) where someone took an uncalibrated DistoX2 and ran it around a survey course on the surface.  By averaging the forward and backward shots he got loop closures around 1% over 400 feet and a dozen stations.  The data using Suunto/tape and a calibrated DistoX2 was not significantly different in the loop closure.

A compass that is 10° (well any degrees off will give a 0% loop error, 
the longer the loop the lower the percentage error, however bad the 
survey. (bit of over simplification, but relatively true) High percent 
loop closure is a poor survey, the opposite is not true.

This could turn into a long interesting debate, please feel free to 
argue with me, let's see how robust our ideas are :-)

Andrew