[Therion] Therion uses wrong declination for surveys 'in the future'

[Matthias Keller]

Hi

Thanks for your effort!

At least for me, this is already a huge improvement. Extrapolating into 
the future is ok for me and would have avoided my problem, so I guess 
the most important points have been adressed.


On 06.10.2020 21:10, Martin Budaj wrote:
>
>     >    I would propose:
>     >
>     >     1. If a survey is dated but is newer than available
>     correction data,
>     >        build should fail with a message like:
>     >        "Error determining magnetic declination for survey <name>
>     with date
>     >        <date>. Please specify the declination explicitly using
>     for example
>     >        'declination 3 deg'"
>     >        instead of the (completely wrong)
>     >        "unable to determine magnetic declination for undated
>     surveys"
>
>
> We have discussed it with Stacho and the following seems to be the 
> best approach:
>
> IGRF models are designed to predict over the 5 year period (IGRF 13 
> released at the end of 2019 is intended to be used to predict the 
> declination up to the end of 2024, when a new version, IGRF 14 will be 
> released). In Therion, we will allow to use the model for additional 5 
> years (using linear extrapolation) and produce a warning (so IGRF 13 
> could be used until the end of 2029). After 2029, more firm warnings 
> will be produced if Therion still uses IGRF 13, but we don't expect 
> anybody to use such an outdated Therion.
The only suggestion I'd have is not only issuing a warning but fail the 
build. In my case I'm starting it from xtherion (on Windows). Warnings 
do not pop out there at all, you even only see a part of the output 
unless you start scrolling, so it's even likely that such a warning will 
not be seen at all - I also only found the other warning in therion 
5.4.4 by chance, as I don't usually examine the output very closely as 
long as it runs through.
> On the other hand: is there any need to use the data older than 1900? 
> If yes, we could implement the GUFM1 model covering the period 1590–1890.
At least for me, I don't think I have performed any surveys before 1900, 
or at least, I cannot remember that ;)
>
>     >     2. If at least one of the imported (and thus joined) surveys
>     has magnetic
>     >        data but at least one does not (or cannot be determined),
>     an error
>     >        shall be thrown as well, because mixing corrected and
>     uncorrected
>     >        surveys is just plain wrong and causes a lot of confusion
>     (as it has
>     >        happened to me). The same error message shall be
>     displayed and the
>     >        build fails.
>
> You can't always avoid mixing dated and undated surveys (sometimes the 
> older survey data might be undated), so using the min(survey_dates) as 
> a proxy for undated surveys (and producing a warning as well) should 
> be a reasonable approach.

I can see your point and for me that's ok - because I don't have any 
undated surveys; I would just find it more consistent the other way - 
mainly because I'm not a huge fan of warning messages that are hard to spot.

Thanks for all your effort

Matt

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