Below a conversation transcript that I
took briefly ‘off forum’, but now time to post it I think.
You can read from the bottom of the
transcript below if you are interested.
Briefly in summary, it seems to me that
since 5.3.5 or earlier, therion loop closure results in grossly distorted
outputs IF there are two or more fixed stations AND (only?) for the stations
that have standard errors specified AND there are survey networks connecting
those fixed stations. Specifying Survex loop closure bypassed this problem.
Since I installed Survex 1.2.8 a few weeks
agoi, my machine has been giving;
“C:\Program
Files\Therion\therion.exe: warning -- can't open cavern output”
when survex loop closure is specified, and
I suspect this is causing Therion to revert to therion loop closure and hence
the distortion problem has been manifesting again if I specify std errors. You
can see samples of my therion.log files in the attached dataset.
Xavier is using Survex 1.2.6 and his log
files, which do not have this problem, are attached separately.
If you are interested you can experiment
with the fixed station statements in the INDEX file in the attached dataset to
see what effect various adjustments have. You might also have to adjust the
loop-closure statement in therion.ini.
So two things to fix; Therions loop
closures and Survex 1.2.8 integration with Therion.
Bruce
From: Bruce [mailto:bruce@tomo.co.nz]
Sent: Friday, 27 December 2013
8:47 a.m.
To:
Subject: fixed point std error
causes extreme survey network distortion
As
commented below.
Bruce
From: Xavier Pennec [mailto:Xavier.Pennec@inria.fr]
Sent: Friday, 27 December 2013
12:48 a.m.
To: Bruce Mutton
Subject: Re: fixed point std error
causes extreme survey network distortion
Hi Bruce,
I just compiled as is and did not get any distortion. However, I have survex
installed: I vaguely remember having some problems using the therion
loop-closure algorithm with some uncertainty on the fixed points a long time
ago (actually problems when survex is not installed, which amounts to using the
therion loop-closure engine). Way back in time
this was the reason I first installed Survex – I had similar problem with
elevations (this one seems mainly a plan problem however)
And then later I had this problem that I posted on the forum
http://article.gmane.org/gmane.comp.gis.therion/2378/match=loop+closure
Indeed, activating therion loop closure (using "loop-closure therion"
in the therion.ini file) distorts the cave …. This might be a side effect of the
loop-closure problem that you reported in 2010 (link above) and which is still unsolved
apparently. Based
on past experience this is what I was expecting, but my current therion.ini is
‘default’ and therion.log reports survex activity, so it seems for
me both survex and therion loop closures are now giving me this effect (5.3.11
and 5.3.12 it seems). I have tried editing therion.ini to explicitly
force both types of loop closure, and the log file reflects what I specify, but
the output is always distorted when there are two or more fixed points and at
least one has std errors specified.
With therion
loop-closure, I get as well with my data some "scraps too large"
errors to produce the pdf output. Same (but also for Survex
closure for me)
Thus, we can conclude to a bug in therion loop-closure. (Historically I agree, but I am perplexed
as to why I now get it with Survex loop closure as well. I have searched
my machine and cannot find any rogue therion.ini files that might be causing
the problem. The log file reports the correct initialization file.
Perhaps there is a clue in the log file entry
“C:\Program Files\Therion\therion.exe: warning -- can't open cavern
output”
Maybe this is causing my machine to revert back to therion loop closure in all
cases?)
…
Xavier
Le 26/12/2013 02:48, Bruce a écrit :