[Therion] Multiple fixes for the same point
andrew at wotcc.org.uk
Sun Sep 10 00:54:57 CEST 2017
Okay I can see your logic, but I'm not sure I agree. However, the following
is a thought dump, which may not be my final position and partly might just
be to argue to check your rohbustness, but hope it helps us all in
First Therion throws an warning not an error for a multiple fix with no
variance, I think this is a big, taking only one result is not useful or
intuitive. Maybe the ultimate answer is Therion to throw an error. (I have
lots of warnings so don't always notice a new one)
That said, a variance is set to other readings, which can be changed, why
treat fix as different. There has never been an exact fix. And yes I can
see the arguement for keeping the status quo, but feel there is a strong
arguement for changing it to a default no zero variance, as I think most
people believe that is what is happening ( yes we should all read the
survex manual in more detail, but often we do not.) Now I do think there is
an agreement to have whether a variance for read off map or GPS should be
set, but maybe some predictive ones a bit like the survey grades is the way
Anyway, I doubt anything will happen, explicitly defining variances will
solve the problem and the programmers have more important things to work
on, but it has been interesting debate and certainly got my head find it
On 9 Sep 2017 10:35 pm, "Bruce Mutton via Therion" <therion at speleo.sk>
> Survex manual https://survex.com/docs/manual/datafile.htm
> *fix* fixes the position of <station> at the given coordinates. … *The
> standard errors default to zero (fix station exactly).* *Cavern will
> give an error if you attempt to fix the same survey station twice at
> different coordinates*, or a warning if you fix it twice with matching
> Further reading about fix and cs in the survex manual explains some
> reasoning and how you can use the implemented behaviour to best effect.
> Therion manual
> *fix* <station> [<x> <y> <z> [<std x> <std y> <std z>]] fix station
> coordinates (with specified errors—only the units transformation, not
> calibration, is applied to them).
> 1. As a beginner, years ago, I took it as self-evident (after reading
> only the Therion manual) that omitting standard errors was tantamount to
> the user telling the software, ‘I want you to fix this position with no
> corrections or adjustments’. I expect this would be the usual assumption,
> for a non-technical user, and the easiest input arrangement. They should
> expect an error if they accidentally apply two fixes to the same station.
> This means all the distortion due to loop closure occurs in survey legs.
> And it means that a user can be confident that they more or less have
> control over what the software is doing.
> 1. The next step is to realise that applying standard errors to fixed
> stations allows the distortion to be shared between the survey leg network
> and the fixed stations. That means fixes for positions of your cave with
> at least two entrances (and at least 2 fixed stations) can self-adjust to
> what is perhaps some sort of best fit.
> 1. For users who want to add another level of complication, as I
> eventually did, the concept of applying multiple coordinates to a single
> fixed station can be used. Requiring standard errors to be defined
> explicitly case by case protects newer users from what would usually be
> unintentional duplication. There are tricks to getting this to work in
> Therion, as the old forum posts I linked to allude to. (I am not even sure
> if they are working in my projects, as I have not focused on those areas
> for a few years – perhaps I should have another look!)
> My vote is squarely with the status quo (with any bugs that may remain in
> step 3 repaired, of course).
> -----Original Message-----
> From: Therion [mailto:therion-bounces at speleo.sk] On Behalf Of Andrew
> Atkinson via Therion
> On 08/09/17 20:47, Bruce Mutton via Therion wrote:
> > As above, I think Therion already provides users with straight forward
> control. Aside from a few quirks and maybe bugs of course.
> Yep I'm sure this is a quirk, maybe even a bug. The default of no variance
> means that multiple entrance co-ordinates cannot be entered in the most
> obvious manor, as currently Therion will only take one of them.
> There is a way round it, that takes experience, it would be better if the
> most obvious way of entering it, did what you might assume, which is what I
> and probably others, especially beginners did/do.
> Therion mailing list
> Therion at speleo.sk
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Therion