[Therion] Cartesian STD for individual legs

[Marcelo Taylor]

*Hi Marcelo,*
Hi Tarquin, thanks for your kind answer.

> These surveys  only
> use tape and clinometer, surveying triangles, starting from two
> coordinates known  stations.

*That's ... both cool and insane at the same time.*

I believe that a typical speleological topographer thing: being a little
bit ingenious and a lot insane...



*Pretty sure a Total Station can cope with this magnetic rock
situation.Perhaps someone else on this list can offer advice...*
For sure, but total stations are expensive, cumbersome and time consuming.
Our idea is to provide a cheap fast way to deal with magnetic anomalous
caves..

> Is there a way to specify specific standard deviations for each leg in
> Therion?

*As far as I know, SD affects all legs specified after it, until another*
*sd command changes it. Similar to the "calibrate" command or "units"*
*command.*
*sd compass 0.3 degrees*
*1 2 12.5 315 17*
*sd compass 0.5 degrees*
*2 3 7.2 220 33*

*It is a Survex command (most things inside a Therion centreline block*
*are a direct copy of their Survex equivalents, and can be passed through*
*to Survex for processing; group/endgroup is an exception, which is*
*begin/end in Survex syntax).*

*I tested it with a loop where every leg is set to sd 0.1, but one single*
*leg set to 200. Therion gave that single leg most of the error.*

Thanks for the suggestion, I will try it for sure. Nevertheless I will
prefer to use cartesian data and dX, dY and dZ notations. It is because
transversal and longitudinal expected errors are very different in
trilateration methodology and I have been able to estimate it in cartesian
coordinates.

I am a little worried if it will also work in "leap-frogging" legs, but I
will check it, for sure.

*If that doesn't work for you, you can use:*
*group*
*sd compass 0.3 degrees*
*1 2 12.5 315 17*
*endgroup*
*group*
*sd compass 0.5 degrees*
*2 3 7.2 220 33*
*endgroup*

*It's quite verbose, but that is explicitly stated as being possible in*
*the Therion book.*

I will try this option too. Right now, that calculations have been done in
an Excell spreadsheet,it is verbose, for sure. But the idea is to include
in our TOPGRU software package (https://see.ufop.br/topgru) in the future.
So, after coding, it will only lead to larger lines centerline blocks, that
can be copied directly into Therion.

TOPGRU right now is only in portuguese and have a more educational
characteristics, but one of our 2021 goals is to release an english version
and maybe moving it to GNU compliant.

*Hope this helps.*

It helped a lot, Tarquin. Many thanks.

Marcelo Taylor
Cel: +55 21 9 9344 5196
marcelo.taylor at gmail.com
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