Error in loop closure algorithm?

[John Halleck]

On Wed, 11 Aug 2004, Olly Betts wrote:

> Date: Wed, 11 Aug 2004 23:16:26 +0100
> From: Olly Betts <olly at survex.com>
> To: Mike McCombe <mikemccombe at btinternet.com>
> Cc: Survex User Group <survex at survex.com>
> Subject: Re: Error in loop closure algorithm?
> 
> On Wed, Aug 11, 2004 at 11:04:43PM +0100, Mike McCombe wrote:
> > Survex moves not only the survey legs in the "bad" loop but also
> > adjusts the connecting leg (i.e. test.4 - test.5) and moves the
> > station in the "good" loop (i.e. test.4) where the connecting leg
> > joins. The "error" is only 1cm which wouldn't show in most cave
> > surveys (with me using the instruments!) . However, the error is still
> > 1cm if you scale the loops down to, say, 1m per leg - which becomes
> > quite noticeable when the loops are small and generally well-closed. 

  Basicly, Least Squares, can smear a blunder all over everything.
  Although whether or not it is very visible varies.

> I'm not seeing this on Linux with Survex 1.0.31.  If I run the second
> example through cavern and then 3dtopos, I get these coordinates:

> (    0.00,     0.00,     0.00 ) test.1
> (   10.00,     0.00,     0.00 ) test.2
> (   10.00,   -10.00,     0.00 ) test.3
> (    0.00,   -10.00,     0.00 ) test.4
> (  -10.00,   -10.00,     0.00 ) test.5
> (  -10.00,    -0.42,     0.00 ) test.6
> (  -20.00,    -1.50,     0.00 ) test.7
> (  -20.00,    -8.92,     0.00 ) test.8
> 
> What operating system are you using?  And which version of Survex?
> 
> Cheers,
>     Olly
> 
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