[Therion] Multiple fixes for the same point

Benedikt Hallinger beni at hallinger.org
Sun Sep 10 11:06:23 CEST 2017


The option to use "alias names" for fixes instead of directly numbers would 
be good, this would allow to ship standards with therion and allow the user 
to to define custom ones, just like in grade definitions.

Why not extend the grades definition to allow specification of fix std 
deviation there?
Btw, I would expect therion to not make assumptions on the fix accuracy 
unless i state it to do so (dont change status quo).

Am 2017-09-10 0:54, schrieb Andrew Atkinson via Therion:
> Bruce
>
> Okay I can see your logic, but Im 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 
> understanding.
>
> 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 dont 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 to 
> go.
>
> 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
>
> Thanks
>
> Andrew
>
> On 9 Sep 2017 10:35 pm, "Bruce Mutton via Therion" <therion at speleo.sk [5]> 
> wrote:
>
>> Survex manual https://survex.com/docs/manual/datafile.htm [1]
>>
>> 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 coordinates.
>>
>> 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).
>>
>>  
>>
>> * 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.
>>
>>  
>>
>> * 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.
>>
>>  
>>
>> * 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).
>>
>> Bruce
>>
>>  
>>
>> -----Original Message-----
>> From: Therion [mailto:therion-bounces at speleo.sk [2]] 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 Im 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.
>>
>>  
>>
>> thanks
>>
>>  
>>
>> Andrew
>>
>>  
>> _______________________________________________
>> Therion mailing list
>> Therion at speleo.sk [3]
>> https://mailman.speleo.sk/listinfo/therion [4]
>
>
> Links:
> ------
> [1] https://survex.com/docs/manual/datafile.htm
> [2] mailto:therion-bounces at speleo.sk
> [3] mailto:Therion at speleo.sk
> [4] https://mailman.speleo.sk/listinfo/therion
> [5] mailto:therion at speleo.sk



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