[Therion] 3d to QGIS - different alignment

[Andrew Atkinson]

Found the problem.

As it, is fake data, it does not have a date. It appears Therion use the 
earliest date for the data is has for undated surveys. This is nearly 9° 
difference between 1965 to today, which is quiet a swing. (I don't know 
what if Therion uses today as the declination if it processes data none 
of which has a date. I guess it just doesn't apply declination, which 
currently for the UK is nearly the same thing)

Solved by setting declination to zero, as the fake data is aligned with 
true north.

Not sure processing surveys that do not have a date with the oldest date 
is the best option. This changes the answer depending on what caves it 
is processed with. Not sure what the right answer is, but I fell 
applying no declination is probably best. Then it either is broken or 
acceptable where ever it is processed.

This leads to the problem that I have lots of old data that I do not 
know the date of, I need to think of the best way to handle this.

thanks

Andrew
On 20/02/2025 11:57, Andrew Atkinson wrote:
> Hi all
> 
> Not strictly a Therion question, but the answer is likely to be in the 
> data entry or the interpretation of data in Therion.
> 
> I'm slowly incorporating QGIS into my workflow, and trying to automate it.
> 
> As such I'm using a modified version of the survex 3d importer
> 
> https://github.com/AndrewAkinson/qgis3-survex-import_amend
> 
> So that items can be easily switched on and off I'm going down the line 
> of importing the 3d files by cave rather than the generated one for the 
> whole catchment
> 
> For now I'm doing it with the data in
> http://www.cave-registry.org.uk/svn/CheddarCatchment/
> 
> Currently I'm working on the Longwood Valley area as Longwood Valley 
> Sink has been recently discovered.
> 
> The directories I'm using
> 
> RRift/ (3d needs to be generated from survex)
> LongwoodValleySink/
> Longwood/ (Fake data with calibrate compass -90!)
> Toothache/ (single leg)
> 
> In each of these directories the .th file generates a survex 3d file
> 
> Also in the the root there is a LongwoodValley.thcfg which has the above 
> caves (plus maybe Charterhouse, GB, TynningsGS and Reads depending on 
> how I left it)
> 
> In the diagram attached (hopefully this list does attachments!)
> 
> The Dark purple dots are the import of the 3d file that has Rhino, 
> Longwood, LongwoodValley Sink and Toothache together. The light pink, 
> yellow dots are the individual imports (and entrances from the MCRA 
> database.) Also included is an overlay of a scree shot from aven, which 
> agrees with the group import.
> 
> The question is why is Longwood different when imported as a 3d on its 
> own compared with as a group? They are both using the same data!
> 
> Andrew
> 
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