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<p><font face="Helvetica, Arial, sans-serif">Hi</font></p>
<p><font face="Helvetica, Arial, sans-serif">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:</font></p>
<p>warning -- unable to determine magnetic declination for undated
surveys</p>
<p>However, firstly: this warning is wrong, as all surveys are dated
correctly.</p>
<p>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.</p>
<p>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</p>
<p>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).</p>
<p>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...</p>
<p>BTW, Therion 5.4.4 seems to have *some* data for 2020 at least,
as it seems:</p>
<p>geomag declinations (deg):<br>
2019.1.1 2.9201<br>
2020.1.1 3.0503</p>
<p>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.</p>
<p>Thanks</p>
<p>Matt<br>
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