[Therion] Joining old and new surveys

Bruce bruce at tomo.co.nz
Tue Feb 17 08:23:31 CET 2015



I have done this a couple of times, although I have always first created a
pseudo survey by making a very (very) crude centerline based on the original
plan and elevation drawings (or plan and estimated altitudes) using a scale
rule and pencil.

I measure overall x and y coords of the pseudo stations (only about 10 or 20
for an entire cave) and use a spreadsheet to calculate delta x and delta y
values for each pseudo leg to enter thus.


   declination 21 deg # is effective with cartesian co-ords, tick

   flags duplicate #prevents length accumulation

   flags approximate


   data cartesian from to northing easting altitude

   7  7a  90  -99  4.5

   7a 9   97 -9 4.5

   9 10   31 -22 0


I then draw a collection of scraps attached to this centerline, and THEN fix
any entrances with known gps coordinates.


Ie Similar to what you have done, but there is a crude centerline that
allows model outputs to be generated as well as map outputs.


Now, whenever we do some modern survey deep in the cave, there is generally
a pseudo station somewhere nearby to connect to.  Of course it will be not
quite in the right place, so we just add another differential pseudo leg
between the closest pseudo station and the estimated position of our new
modern survey.


Some related information in this link that seems closer to what you have
done (but not what I have followed


Not sure if the above will be that helpful, given you have progressed as far
as you have, but hopefully give you some ideas.





From: therion-bounces at speleo.sk [mailto:therion-bounces at speleo.sk] On Behalf
Of Steven Tucker
Sent: Tuesday, 17 February 2015 7:15 p.m.
To: therion at speleo.sk
Subject: [Therion] Joining old and new surveys



I have an old survey from the 80s and I have new sections that I want to add
with Therion. The old survey has no centerline data. 

I have redrawn the old survey in a th2 file and allocated 3 points which
correspond to 3 different entrances. In the th file I have given coordinates
to all 3 of those points. This works perfectly. 

I am struggling to connect the new section with this old section. The new
section starts in a deep section of the cave and is far away from any of my
currently defined points. 

What is the easiest way to connect the new and old sections?



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