[Therion] Declination and meridian convergence

Wolfgang Zillig wolfgang.zillig at web.de
Tue Oct 4 17:51:37 CEST 2011


Hi,

I'm a little bit confused at the moment how to correct for declination 
and meridian convergence.

Question 1: Is it correct that in therion and in survex the declination 
is specified exactly the opposite way?

Therion handbook page 18:
true bearing = measured bearing + declination

Survex 1.2.1 manual page 19:
(true bearing)=((bearing)-(declination zero err))

So in case that magnetic north is 2° east of geographic north, I have to 
correct this in therion by -2 and in survex by +2.

If this is correct, could you please add a warning note to the therion 
manual!


Question 2:
When I enter the measurement data in therion, the meridian convergence 
is handled automatically (in case a "cs" is specified). However due to 
historic reasons most of our data is still in survex format. I import 
the ".3d" file and specify the "cs" during import. I assume that therion 
is not applying any corrections for the meridian convergence and I need 
to correct the bearings manually in survex?



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