Re: [Therion] Magnetic declination

[Martin KERN via Therion]

Hi everyone,

Many thanks for you replies.
I have all answers to my problems.

@Olly, your messages about magnetic declination are very relevant.
I also believe it could be clearer. You can write something on wiki?
I’ll do the same on french wiki.

Martin K.
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Re: [Therion] Magnetic declination

[Olly Betts via Therion]

On Fri, Mar 02, 2018 at 05:57:26PM +0100, Radek via Therion wrote:
> Here's more accurate
> 
> https://www.ngdc.noaa.gov/geomag-web/#declination

That uses the same model as Therion does, so I can't see why it should
be more accurate (unless you're using a version of therion more than a
year old, as before https://github.com/therion/therion/pull/52 Therion
calculated the fraction of the year to use in a slightly odd way, though
even then the difference is tiny if you're specifying a full date).

Also, if you look up values by hand and specify them explicitly to
therion you are hard coding the answers for the current version of the
IGRF model.  But each generation of the IGRF model is necessarily
predictive for dates after it was issued and is only declared to be
definitive for dates more than 5 years before it was issued.  So each
new generation of the model can change the declination figures reported
for the last 10 years compared to the previous generation (and the new
answers should be expected to be better).

As Xavier suggests, the table of reported declinations in the log is for
the start of each year, but declinations used for surveys are calculated
for the actual survey dates.

Maybe this needs making clearer somehow, as this isn't the first time
this summary table has led someone to think that the declination was
only being calculated for the start of each year:

https://mailman.speleo.sk/pipermail/therion/2017-February/006241.html

Cheers,
Olly
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Re: [Therion] Magnetic declination

[Xavier Pennec via Therion]

If I remember correctly, the declination is displayed on the log file 
for the beginning of all the years for which you have some survey data, 
but it is interpolated in between these measurements with the exact date 
for each survey environment where you provided a date.


Xavier

Le 02-Mar-18 à 17:22, Martin KERN via Therion a écrit :

Thanks for your reply Ladislav.

I know that but the automatic declination is calculated for the first 
januray of the year which is enter, not for the exact date.

It's not a probleme for the accuracy of the survey ?

Martin K.

Le 2 mars 2018 17:05, "Ladislav Blažek" > a écrit :


Hi,

declination should be calculated automatically based on the survey
date.
Declination parameter is for manual correction.

\LB

2. 3. 2018 v 16:29, Martin KERN via Therion mailto:therion@speleo.sk>>:


Quick question concerning the magnetic declination.

How you indicate it?

Just by entering the date or with the command ?

Because when I just specify the date, the declination which is
calculate is for the first January, even if I specify another
month in the centreline (e.g. 28.08.2017). Consequently,
centreline is slightly offset that if I enter the real
declination for the date.

I don’t know if this shift is important for survey accuracy or if
I can ignore it ?

Thanks and sorry for all my questions.

Martin K.


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--

-
Xavier Pennec
Senior Research Scientist / Directeur de recherche
Asclepios project-team, INRIA Sophia-Antipolis
2004 Route des Lucioles, BP93
F-06902 Sophia-Antipolis Cedex, France
+33 4 92 38 76 64
+33 6 78 35 16 90
http://www-sop.inria.fr/asclepios/
---


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Re: [Therion] Magnetic declination

[Henry.Bennett--- via Therion]

The variation throughout the year is fairly minimal and I don’t believe it is 
statistically relevant to worry about the data collection month.

Henry

From: Therion [mailto:therion-boun...@speleo.sk] On Behalf Of Martin KERN via 
Therion
Sent: 02 March 2018 16:22
To: Ladislav Blažek 
Cc: Martin KERN ; List for Therion users 

Subject: Re: [Therion] Magnetic declination

Thanks for your reply Ladislav.

I know that but the automatic declination is calculated for the first januray 
of the year which is enter, not for the exact date.
It's not a probleme for the accuracy of the survey ?

Martin K.

Le 2 mars 2018 17:05, "Ladislav Blažek" 
mailto:ladis...@lblazek.cz>> a écrit :
Hi,

declination should be calculated automatically based on the survey date.
Declination parameter is for manual correction.
\LB

2. 3. 2018 v 16:29, Martin KERN via Therion 
mailto:therion@speleo.sk>>:
Quick question concerning the magnetic declination.
How you indicate it?
Just by entering the date or with the command ?
Because when I just specify the date, the declination which is calculate is for 
the first January, even if I specify another month in the centreline (e.g. 
28.08.2017). Consequently, centreline is slightly offset that if I enter the 
real declination for the date.
I don’t know if this shift is important for survey accuracy or if I can ignore 
it ?

Thanks and sorry for all my questions.
Martin K.

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Re: [Therion] Magnetic declination

[Radek via Therion]

Here's more accurate





https://www.ngdc.noaa.gov/geomag-web/#declination





Radek S.___
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Re: [Therion] Magnetic declination

[Philippe Vernant via Therion]

Hi Martin,

Just to be sure, but I guess you already know it, you also have to enter the 
coordinate for the calculation of the declination. 

Phil


> On 02 Mar 2018, at 17:22 PM, Martin KERN via Therion  
> wrote:
> 
> Thanks for your reply Ladislav.
> 
> I know that but the automatic declination is calculated for the first januray 
> of the year which is enter, not for the exact date.
> It's not a probleme for the accuracy of the survey ? 
> 
> Martin K. 
> 
> Le 2 mars 2018 17:05, "Ladislav Blažek"  > a écrit :
> Hi,
> 
> declination should be calculated automatically based on the survey date.
> Declination parameter is for manual correction.
> 
> \LB
> 
> 2. 3. 2018 v 16:29, Martin KERN via Therion  >:
> 
>> Quick question concerning the magnetic declination.
>> 
>> How you indicate it?
>> 
>> Just by entering the date or with the command ?
>> 
>> Because when I just specify the date, the declination which is calculate is 
>> for the first January, even if I specify another month in the centreline 
>> (e.g. 28.08.2017). Consequently, centreline is slightly offset that if I 
>> enter the real declination for the date.
>> 
>> I don’t know if this shift is important for survey accuracy or if I can 
>> ignore it ?
>> 
>>  
>> Thanks and sorry for all my questions.
>> 
>> Martin K.
>> 
>> 
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>> 
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Re: [Therion] Magnetic declination

[Martin KERN via Therion]

Thanks for your reply Ladislav.

I know that but the automatic declination is calculated for the first
januray of the year which is enter, not for the exact date.
It's not a probleme for the accuracy of the survey ?

Martin K.

Le 2 mars 2018 17:05, "Ladislav Blažek"  a écrit :

> Hi,
>
> declination should be calculated automatically based on the survey date.
> Declination parameter is for manual correction.
>
> \LB
>
> 2. 3. 2018 v 16:29, Martin KERN via Therion :
>
> Quick question concerning the magnetic declination.
>
> How you indicate it?
>
> Just by entering the date or with the command ?
>
> Because when I just specify the date, the declination which is calculate
> is for the first January, even if I specify another month in the centreline
> (e.g. 28.08.2017). Consequently, centreline is slightly offset that if I
> enter the real declination for the date.
>
> I don’t know if this shift is important for survey accuracy or if I can
> ignore it ?
>
>
>
> Thanks and sorry for all my questions.
>
> Martin K.
>
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>
>
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Re: [Therion] Magnetic declination

[Ladislav Blažek via Therion]

Hi,

declination should be calculated automatically based on the survey date.
Declination parameter is for manual correction.

\LB

2. 3. 2018 v 16:29, Martin KERN via Therion :

> Quick question concerning the magnetic declination.
> 
> How you indicate it?
> 
> Just by entering the date or with the command ?
> 
> Because when I just specify the date, the declination which is calculate is 
> for the first January, even if I specify another month in the centreline 
> (e.g. 28.08.2017). Consequently, centreline is slightly offset that if I 
> enter the real declination for the date.
> 
> I don’t know if this shift is important for survey accuracy or if I can 
> ignore it ?
> 
>  
> 
> Thanks and sorry for all my questions.
> 
> Martin K.
> 
> 
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