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

Mon Oct 5 23:54:59 CEST 2020

Exactly this.

Unfortunately, even the current Therion 5.5.1 doesn't have a more 
meaningful (and correct) message than "unable to determine magnetic 
declination for undated surveys"

One can argue whether 0 or an extrapolated value would be better, but 
failing with a good error message would be the best way to handle this. 
Assuming 0 for undated surveys is probably sensible, however mixing 
surves with available data and without data is always just plain wrong 
(except if you're living exactly where the magnetic derivation is 0° ;) 
) and should fail.

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"
 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.

Is this the right place to request that or shall I open an issue on github?

I really find this issue pressing, because I just cannot imagine, that 
this doesn't happen to everyone here from time to time - keeping therion 
up to date is not the same cycle as adding new surveys, and suddenly you 
fall out of the prediction data.

btw, is there any way to update the data in an existing therion 
installation? Or is the only way the update to a (hopefully existing) 
new version?

Thanks

Matt

On 05.10.2020 21:38, Benedikt Hallinger wrote:
> Falling hard with an appropriate error message would be good: it’s 
> obvious then that the available data is invalid, and why. And the 
> message should include the hint to the declination command to fix this.
>
>> Am 05.10.2020 um 20:40 schrieb Bruce Mutton <bruce at tomo.co.nz>:
>>
>> 
>>
>> Hi Matt
>>
>> I think these issues have been raised previously.
>>
>> The error message for dates later than those included in the Therion 
>> model was inaccurate, as you point out.  I ‘think’ that in recent 
>> versions this may have been replaced with a more meaningful message.
>>
>> And then the question of whether it is better for Therion to 
>> extrapolate future declinations, or set them to zero?
>>
>> Shades of failing gracefully or abruptly, I guess.  I could take 
>> either side, but I think my preference would be for Therion to set 
>> declinations beyond those modelled to zero.  This way it is more 
>> likely that users will detect the problem (as you have), and either 
>> upgrade to a more recent version of Therion, or manually set the 
>> declination for each affected survey, using the declination statement.
>>
>> Bruce
>>
>> *From:*Therion <therion-bounces at speleo.sk> *On Behalf Of *Matthias Keller
>> *Sent:* Monday, 5 October 2020 21:40
>> *To:* therion at speleo.sk
>> *Subject:* [Therion] Therion uses wrong declination for surveys 'in 
>> the future'
>>
>> Hi
>>
>> I just had the following problem: A current survey (with survey dates 
>> 2020.06.27 and 2020.09.19) was compiled using Therion 5.4.4 (from 
>> 2019). I got the following warning during compilation:
>>
>> warning -- unable to determine magnetic declination for undated surveys
>>
>> However, firstly: this warning is wrong, as all surveys are dated 
>> correctly.
>>
>> However I was stunned by some large loop errors in the newest surveys 
>> (>60cm in only 10 legs). Then, just by some other impulse I updated 
>> therion to 5.5.1 and suddenly, those errors went down to <10cm and 
>> the generated models looked differently. Also, the above error 
>> message was not present anymore.
>>
>> So i experimented and just added "declination 3 deg" to the two new 
>> surveys (from June and September) and suddenly, the output generated 
>> by 5.4.4 looked pretty much as the one from 5.5.1
>>
>> It appears that, when therion cannot determine the magnetic 
>> declination of a survey (with valid date!), it finally just assumes 
>> 0. The problem seems to be, that the declination data stored in 5.4.4 
>> didn't let therion determine a possible declination for 2020.06.27 
>> and 2020.09.19 so it just assumed 0. I would have expected therion to 
>> at least consider the latest known declination which would result to 
>> around 3° (in Switzerland).
>>
>> Is this a known issue? It just means that whenever you open a survey 
>> in some version being 'too old', it will kill your plans...
>>
>> BTW, Therion 5.4.4 seems to have *some* data for 2020 at least, as it 
>> seems:
>>
>> geomag declinations (deg):
>>   2019.1.1  2.9201
>>   2020.1.1  3.0503
>>
>> but the only surveys from 2020 are the ones from June 2020 and 
>> September 2020, and both were assigned a declination of 0° instead of 
>> about 3°. I can verify that by adding the declination parameter with 
>> "0 deg" to those surveys and the output is identical to the one 
>> without this parameter.
>>
>> Thanks
>>
>> Matt
>>
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