[Therion] Multiple fixes for the same point

Bruce Mutton bruce at tomo.co.nz
Fri Sep 8 21:47:08 CEST 2017

>From Andrews post

>Now one of the answers which I might start to do is always be explicit in the variance, however, is it really reasonable for survex and therefore therion to assume a fix is perfect, we know that they are not. 

That is the right approach I think Andrew.  I have always omitted variance when I want Therion to assume a fix is perfect (knowing of course it is not quite perfect) and included a variance on EVERY fixed point I want therion to adjust in the same way it adjusts survey legs.  The variance is analogous to survey grade or sd, and so we tweak each in every survey according to the perceived quality of each component (if we want to, otherwise just ignore it).

> gps locations fixed by survey legs all the error is distributed to the survey legs, does not seem right.
So what I'm suggesting is that the default for fix to be perfect should be looked at and maybe amended to almost perfect variance.

As above, I think Therion already provides users with straight forward control.  Aside from a few quirks and maybe bugs of course.
Guidance on typical fixed point variances for common devices and coordinate sources would not go amiss however.


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