[Therion] Declination and the cs command

[John Stevens]

Thank you for the answer, I now see that Therion deals with declination in a 
slightly different way to Survex. So i will need to adjust all the 
calibrated  data I have converted from Survex. It also explains why the gaps 
(closures) between caves has changed when some data was imported using a .3d 
file from Survex and others with the data converted into Therion.
Rather than going through all my files and finding out the differing 
meridian convergence for each file and changing the declination figures. 
(this would make it hard to see where these figures have come from). Is 
there any problem with setting a compass calibration to take care of the 
meridian convergence and use my old declination readings? As in the attached 
file.

John

-----Original Message----- 
From: Stacho Mudrak
Sent: Friday, October 05, 2012 1:22 PM
To: List for Therion users
Subject: Re: [Therion] Declination and the cs command

The problem of your sample data is, that you have cs specification
after fix command in centerline.

If you put cs OSGB:SO before "fix 1 10000 10000 0", then it starts to
behave as it should. Otherwise this fix is in local coordinate system.

Declination in therion is allways agains true north. So just
substracting "meridian convergence" from declination specification
should solve your problem.

S.

On 3 October 2012 16:41, John Stevens <john at k-stevens.co.uk> wrote:
> The calibrations were to grid north not true north
> The little file help illustrate the problem. Either declination statement
> can be used (or both, as they don’t stack).
> If the cs command is commented out, we get a level square, but a rotated
> square if the cs command is used.
> So that was the solution, the difference between grid and true north.
>
> I then used the north true command and this rotated it to be level, north
> grid then moved it back. So back to north true.
> I am now unable to reproduce the the twisted again. I seem to be locked 
> into
> this north command.
> Even when the declinations are commented out, I cant get it to use the cs
> declinations. Whoops!
> (yep I did restart the computer with no joy)
>
> John
>
>
> From: Stacho Mudrak
> Sent: Wednesday, October 03, 2012 2:04 PM
> To: List for Therion users
> Subject: Re: [Therion] Declination and the cs command
>
> If declination is explicitly specified for centerline, automatic 
> declination
> is turned off.
>
> The reason, why you have a rotated map is probably "meridian convergence". 
> I
> am not an expert in this topic, but coordinate system north is usually 
> also
> rotated against true astronomical north.
>
> Have you played with layout north settings? E.g. include:
>
> north grid
>
> in the layout? Are you able to measure somehow this artificial rotation?
> Therion in its output reports both - calculated magnetic declination and
> meridian convergence for cave area.
>
> Another question? Do you measure declination against true (astronomical) 
> or
> grid north?
>
> S.
>
> On 3 October 2012 13:54, John Stevens <john at k-stevens.co.uk> wrote:
>>
>> It seems the cs command over writes any declination that has been set,
>> using the date provided with the survey data.
>>
>> I have a large batch of old data with some accurate local declinations
>> given. Unfortunately these are overridden so I can’t compare my results 
>> with
>> the original results.
>> How can I make sure my local declinations are used rather than the cs
>> global declination.
>>
>> Another problem on the same line. I have a set of data where the
>> declination has been taken off the bearings, so the local declination is 
>> now
>> 0 degrees but the cs command still adds a declination, moving it way out
>> from its expected line.
>>
>> Can we have therion having a priority for local declinations rather than
>> the gobal cs delinations ?
>>
>> John
>>
>>
>> _______________________________________________
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>> Therion at speleo.sk
>> http://mailman.speleo.sk/mailman/listinfo/therion
>>
>
>
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