I second Ollies advice.
I'm a Therion user (not Survex), although I use survex loop closure.  That 
gives some additional statistics in the Therion log file, but not the loop 
error standard deviations.  I wonder if Therion (or Cavern) could incorporate 
these in the log file, or if Aven could be made to list them?

The graphical presentation in Aven is of course the best, but sometimes a 
written list is useful as well.


-----Original Message-----
From: Therion <therion-boun...@speleo.sk> On Behalf Of Olly Betts
Sent: Friday, 16 August 2019 09:06
To: MD <m...@foxel.org>
Cc: therion@speleo.sk
Subject: Re: [Therion] Detecting errors

On Thu, Aug 15, 2019 at 10:17:00AM +0200, MD wrote:
> I wonder what people use to find errors. For example im I have too 
> loops L1 and L2 and L1 is “good” (0.1% error) while L2 is “bad” (4%
> error) i can assume that the error is in the stations/shots which are 
> part of L2 but not L1. Is there an automated approach for that?

I would avoid looking at the percentage error - what's reasonable varies 
depending on the number of legs in the loop, and also how long the legs are, so 
you can't simply compare the percentage errors for two different loops.

What's more useful is what the observed error is compared to what you'd expect 
the error to be based on the grade(s) of the survey(s).  The grades say things 
like "compass readings within one degree" and from that you can work out what 
you'd expect the error for each leg to be (in 3 dimensions) and sum those to 
get the expected error for each traverse.

Benedikt's suggestion to view coloured by error in aven is where I would start 
(right click on the colour key is the easiest way to change what to colour by). 
 This shows you each traverse coloured by its error measured in standard 
deviations - assuming the grades are appropriate then 99.7% of readings should 
be within 3 standard deviations:


The colour scale is fixed such that blue is "good" and anything else is 
suspect.  You probably want to look at the worst first.

Once you have a suspect traverse identified, you can look it up in the .err 
file which is produced alongside the .3d file when you process the data.  
Here's an example entry:

76.brave.18 - 76.brave.17 - 76.brave.16 - 76.brave.15 - 76.brave.14 - 
76.brave.13 - 76.brave.12 - 76.brave.11 - 76.brave.10
Original length  32.35m (  8 legs), moved   1.26m ( 0.16m/leg). Error   3.90%
H: 5.888476 V: 0.864600

Here 4.920289 is the number of sds (which is what aven colours by).  But below 
that the H and V are the equivalent numbers looking only at the horizontal and 
vertical errors.  So here the vertical error is very good, and the horizontal 
error lousy.  That suggests the error is probably either in a compass reading 
or the tape reading in a low-inclination leg.  (If H was fine and V bad, you'd 
be looking for a clino error or a tape error in a steep leg or plumb.)

So you can now look at each of the legs in the list on the first line and look 
at their compass readings and the tape readings for any low-inclination legs.  
For manually entered data, compare with the original notes.

It's still somewhat manual, but at least you can narrow down where to look 

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