[Therion] Fix station point using only 2D

Graham Mullan graham.mullan at coly.org.uk
Wed Aug 22 23:35:03 CEST 2018 

I think there are two issues here. I have skewed surveys built on 2D data using 3D fixed points and that seems, to me, to be what is happening here.

Firstly, if your radiolocation point has no depth information then you cannot use it for a 3D skew which I think (I may be wrong) as it is insufficiently accurate.

Secondly, if your survey is both only in 2D and has an apparent error of as much as 150 m from the radiolocation point then there is something wildly wrong with the data.

Your best bet - and yes I have been forced to do exactly this - is to resurvey the cave to 3D standards, whether this be compass/clino or Distox and start again.

Sorry, but your dataset is simply not good enough. 

Graham

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Today's Topics:

   1. Re: Fix station point using only 2D (kevin dixon)
   2. Re: Fix station point using only 2D (Martin Sluka)
   3. Re: Fix station point using only 2D (Xavier Pennec)
   4. Eurospeleo 2018 (Stacho Mudrak)


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Message: 1
Date: Tue, 21 Aug 2018 11:06:05 +0100
From: kevin dixon <geospatial3d at gmail.com>
To: List for Therion users <therion at speleo.sk>
Subject: Re: [Therion] Fix station point using only 2D
Message-ID:
	<CAAUsM+Nn7MgMkKaSMuJJhfVwTvot2RiNcnHdS5+RuP97D_2iAA at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Adam,

Radio-location can give you depth but accuracy is not too good.
How have your surface positions at the entrance(s) and the radio location been determined ?
Professional GNSS (~3cm), DGPS(~1m) or hand held (~3m) ?

I have radio-location fixes at the far end of a system to control any accumulated azimuth bias.
For these I have assigned an elevation to the radio-location equivalent to the cave survey at the radio location point and used an appropriate SD value for the radio location data. You may have to iterate a few times and experiment with SD values to see how it changes your survey with and without the radio location fix(s).

Also better if you have radio location fixes at different points because geology effects the position.
Use several in the survey - you should see how they fit (or not) - reject the wildly out ones, adjusting to the rest will help reduce any bias.

150m is a lot of difference so I would be looking at the positional method used, datum and grid, survey instrument calibrations, declination values and then get additional radio locations to confirm. If you are dealing with older survey data then you may want to consider a compass bias - does a survey rotation significantly reduce the difference ?

Kevin Dixon

On Tue, Aug 21, 2018 at 10:41 AM, Adam Pyka via Therion <therion at speleo.sk>
wrote:

> Hi all,
>
> How to 'fix' the survey station point (to morph the cave plan) having 
> only 2D coordinates?
>
> Using the radiolocation we get (with quite good accuracy) the station 
> point position which is about 150m beyond the estimated location we 
> get from surveying. So now I wanted to use this position to make a 
> correction to the main polygon. But the 'fix' command need a 3D coords 
> so how should I do that (no, there is no point to measure the depth by 
> radiolocation by some reasons).
>
> Thanks in an advice,
> Adam
> _______________________________________________
> Therion mailing list
> Therion at speleo.sk
> https://mailman.speleo.sk/listinfo/therion
>
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Message: 2
Date: Tue, 21 Aug 2018 12:22:11 +0200
From: Martin Sluka <martinsluka at mac.com>
To: List for Therion users <therion at speleo.sk>
Subject: Re: [Therion] Fix station point using only 2D
Message-ID: <8151B013-8CA1-49AC-B486-478CD9643904 at mac.com>
Content-Type: text/plain; charset=utf-8

Add label altitude to that station and use it. 


Odesláno z iPhonu

21. 8. 2018 v 11:46, Henry.Bennett--- via Therion <therion at speleo.sk>:

> Assuming that you've got another fix for the entrance then you should be able to get the height for the end station.  Just look at the .3d file.  That will give you the relative altitude at the end - just use that.
> 
> Henry
> -----Original Message-----
> From: Therion <therion-bounces at speleo.sk> On Behalf Of Adam Pyka via 
> Therion
> Sent: 21 August 2018 10:42
> To: therion at speleo.sk
> Cc: Adam Pyka
> Subject: [Therion] Fix station point using only 2D
> 
> Hi all,
> 
> How to 'fix' the survey station point (to morph the cave plan) having only 2D coordinates?
> 
> Using the radiolocation we get (with quite good accuracy) the station point position which is about 150m beyond the estimated location we get from surveying. So now I wanted to use this position to make a correction to the main polygon. But the 'fix' command need a 3D coords so how should I do that (no, there is no point to measure the depth by radiolocation by some reasons).
> 
> Thanks in an advice,
> Adam
> _______________________________________________
> Therion mailing list
> Therion at speleo.sk
> https://mailman.speleo.sk/listinfo/therion
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> Company details for other Dell UK entities can be found on  www.dell.co.uk.
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------------------------------

Message: 3
Date: Tue, 21 Aug 2018 13:16:28 +0200
From: Xavier Pennec <Xavier.Pennec at inria.fr>
To: therion at speleo.sk
Subject: Re: [Therion] Fix station point using only 2D
Message-ID: <ebf6a718-3103-5437-1707-eb3abf8e1299 at inria.fr>
Content-Type: text/plain; charset=utf-8; format=flowed

The altitude needs indeed to be given, but you should also specify that it is highly unreliable by giving it a every high standard deviation, like:
fix MyRadioLocation   accurate_x_coord   accurate_y_coord approximate_altitude 3 3 1000 # stddev of 3m in x and y and 1000m in z This should guaranty that this fixed station will not have a big influence on the altitude in the loop error compensation algorithm.

Xavier


Le 21-Aug-18 à 12:22, Martin Sluka via Therion a écrit :
> Add label altitude to that station and use it.
>
>
> Odesláno z iPhonu
>
> 21. 8. 2018 v 11:46, Henry.Bennett--- via Therion <therion at speleo.sk>:
>
>> Assuming that you've got another fix for the entrance then you should be able to get the height for the end station.  Just look at the .3d file.  That will give you the relative altitude at the end - just use that.
>>
>> Henry
>> -----Original Message-----
>> From: Therion <therion-bounces at speleo.sk> On Behalf Of Adam Pyka via 
>> Therion
>> Sent: 21 August 2018 10:42
>> To: therion at speleo.sk
>> Cc: Adam Pyka
>> Subject: [Therion] Fix station point using only 2D
>>
>> Hi all,
>>
>> How to 'fix' the survey station point (to morph the cave plan) having only 2D coordinates?
>>
>> Using the radiolocation we get (with quite good accuracy) the station point position which is about 150m beyond the estimated location we get from surveying. So now I wanted to use this position to make a correction to the main polygon. But the 'fix' command need a 3D coords so how should I do that (no, there is no point to measure the depth by radiolocation by some reasons).
>>
>> Thanks in an advice,
>> Adam
>> _______________________________________________
>> Therion mailing list
>> Therion at speleo.sk
>> https://mailman.speleo.sk/listinfo/therion
>> Dell Corporation Limited is registered in England and Wales. Company 
>> Registration Number: 2081369 Registered address: Dell House, The Boulevard, Cain Road, Bracknell,  Berkshire, RG12 1LF, UK.
>> Company details for other Dell UK entities can be found on  www.dell.co.uk.
>> _______________________________________________
>> Therion mailing list
>> Therion at speleo.sk
>> https://mailman.speleo.sk/listinfo/therion
> _______________________________________________
> Therion mailing list
> Therion at speleo.sk
> https://mailman.speleo.sk/listinfo/therion

-- 
> -------------------------
> Xavier Pennec
> Senior Research Scientist / Directeur de recherche Asclepios 
> project-team, INRIA Sophia-Antipolis
> 2004 Route des Lucioles, BP93
> F-06902 Sophia-Antipolis Cedex, France
> +33 4 92 38 76 64
> +33 6 78 35 16 90
> http://www-sop.inria.fr/asclepios/
> -------------------------------



------------------------------

Message: 4
Date: Tue, 21 Aug 2018 15:38:35 +0200
From: Stacho Mudrak <lists at group-s.sk>
To: List for Therion users <therion at speleo.sk>
Subject: [Therion] Eurospeleo 2018
Message-ID:
	<CAP35+gG_86zAvQC1t8XJ8iCuSu=kf8DhDqcTa7ogcuka=W7=XQ at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hi everybody,

eurospeleo meeting in Austria starts tomorrow. Me and Martin (Budaj), we are leaving there tomorrow and we will be there until Surveying workshop on Sunday afternoon. If you are interested, we could meet at welcome ceremony.


S.
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