[Therion] Fix station point using only 2D

[Graham Mullan via Therion]

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

-Original Message-
From: Therion  On Behalf Of therion-requ...@speleo.sk
Sent: 22 August 2018 12:00
To: therion@speleo.sk
Subject: Therion Digest, Vol 152, Issue 9

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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)


--

Message: 1
Date: Tue, 21 Aug 2018 11:06:05 +0100
From: kevin dixon 
To: List for Therion users 
Subject: Re: [Therion] Fix station point using only 2D
Message-ID:

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 
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
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Message: 2
Date: Tue, 21 Aug 2018 12:22:11 +0200
From: Martin Sluka 
To: List for Therion users 
Subject: Re: [Therion] Fix station point using only 2D
Message-ID: <8151b013-8ca1-49ac-b486-478cd9643...@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 :

> 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  On Behalf Of Adam Pyka via 
> Therion
> Sent: 21 August 2018 10:42
> To: therion@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 

Re: [Therion] SDs for distoX surveys

[Graham Mullan via Therion]

I am not sufficiently versed in the maths to suggest what figures might be
used, but I do want to know why you think that the 3-times feature might
affect the expected error for the angles but not for the length?

Graham

-Original Message-
From: Survex  On Behalf Of Wookey
Sent: 04 August 2018 01:37
To: Survex User Group ; Therion List 
Subject: SDs for distoX surveys

Has anyone thought about what the correct SDs for distoX/distoX2 (as opposed
to compass and tape) surveys are?  I reckon distoX surveys have
significantly lower expected error, due to the 'measure 3 times'
leg feature (if used) and just higher accuracy due to instrument itself,
ease of taking readings (no need to get head near station), and no
difficulties with steep legs > 15 degrees.

Seems to me this means that we should be using different SDs for these
surveys (at least for bearing and inclination readings - length is not
obviously more reliable), but I'm not sure how to quantify those
improvements.

Anyone got any ideas what numbers to use?

Wookey
--
Principal hats:  Linaro, Debian, Wookware, ARM http://wookware.org/

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[Therion] TerrainTool

[Graham Mullan via Therion]

Mike McCombe's TerrainTool has been fixed and is available again from 
http://www.ubss.org.uk/terraintool/terraintool.php Download and enjoy.

It may not use the latest data but it remains the most straightforward way of 
adding topographic detail to Therion 3D models.

Graham

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[Therion] Development 5.4.1+4369eea inverts and recolours altitude

[Graham Mullan via Therion]

Are we talking about relative numbers (depth of cave) or absolute numbers 
(height above sea level)? The former may run differently to the latter. I 
usually use absolute numbers, if at all possible.

Graham

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Re: [Therion] Therion Digest, Vol 143, Issue 1

[Graham Mullan via Therion]

Ben Cooper wrote:

Is there a way to incorporate Theodolite data into Therion?

We dealt with historic theodolite data by fudging it and using the generated 
legacy listing of fixed points. However, when needing to use a total station in 
an area of a show cave with too much ironmongery to use magnetic instruments, 
we took a magnetic bearing on the first total station leg and took that as a 
baseline.

Graham 

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Re: [Therion] Exporting 3d models

[Graham Mullan via Therion]

What about webgl, does Therion support it?

-Original Message-
From: Martin Sluka [mailto:martinsl...@mac.com] 
Sent: 21 October 2017 17:02
To: List for Therion users <therion@speleo.sk>
Cc: Graham Mullan <graham.mul...@coly.org.uk>
Subject: Re: [Therion] Exporting 3d models

What about webgl?

m.s. 

Odesláno z iPhonu

21. 10. 2017 v 15:23, Graham Mullan via Therion <therion@speleo.sk>:

> Is there any plan to allow the export of lox models in pdf format, so 
> that they can be manipulated in Adobe Acrobat Reader? This would allow 
> 3d models to be viewed more widely, by users who otherwise have no 
> need to download & install Therion.
> 
> Graham
> 
> graham.mul...@coly.org.uk
> 
> 
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[Therion] Exporting 3d models

[Graham Mullan via Therion]

Is there any plan to allow the export of lox models in pdf format, so that
they can be manipulated in Adobe Acrobat Reader? This would allow 3d models
to be viewed more widely, by users who otherwise have no need to download &
install Therion.

Graham

graham.mul...@coly.org.uk


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Re: [Therion] How to do better join from scraps in different .th2

[Graham Mullan via Therion]

Am I reading this correctly? You are saying that Topodroid exports every scrap 
as an individual pair of .th and .th2 files? If that's the case, you don't need 
a protocol for working in Therion, you need to writers of Topodroid to alter 
their export protocols so that your entire day's surveying is exported as a 
single pair of .th and .th2 files which you can break down into scraps as you 
wish. My reading of this as it seems to stand would have every X-section 
exported as separate .th and .th2 files, which is just ridiculous.

Have I got something wrong?

Graham

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Re: [Therion] Multiple fixes for the same point

[Graham Mullan via Therion]

Andrew has shown up an interesting flaw in both Therion and Survex. A single 
fix of a point, unless otherwise qualified, will always be presumed to be more 
accurate than multiple fixes than multiple fixes even though (I suppose, I 
don't have the maths) the latter should be better. Unless one is using a decent 
dGPS system to fix the points, it is also potentially the case that the 
relationship between two fixed points at entrances will be better described by 
the intervening underground survey data than by the GPS fixes made using 
consumer hand-held devices.

I will soon have to be dealing with a similar problem with a multi-entrance 
cave as the various lines of data join up - like Andrew's this is a dataset 
obtained on expo and I'll not get any more data until next year so 'soon' is a 
bit wrong. I think we will solve this by getting as good a fix as possible for 
one entrance and then using our survey data to delimit the other entrances. 
I'll also, however collect GPS records of the same spots and highlight the 
differences.

The answer may be to insist that fixed point data must include an estimate of 
precision and that non-entry for that field would default to something worse 
than an exact fix.

I have, in the past done this the other way around, though. I have a dataset 
for one relatively linear multi-entrance cave, but the data is very old and was 
not collected using an inclinometer, passage gradients are generally of the 
order of 2-3 degrees. So I used the fixed points for the entrances to skew the 
profile of the cave. The resulting model was a reasonable facsimile of reality.

Graham

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[Therion] Mud and clay

[Graham Mullan via Therion]

Rob Countess wrote:

" Well, in my mind, clay is a more specifically defined substance based on 
mineral content and particle size. Mud is larger particles, more organics, and 
less homogenous. Clay is what you make pots from and is less frequent in 
Canadian caves in my experience ..."

Clay is something more of a technical term and means a sediment with particle 
sizes in the range  0.98–3.9 µm. This is finer than silt and much finer than 
sand. Mud, on the other hand is not a technical term being defined as a mixture 
of 'earth' or 'dirt' and water. It is difficult to think of a circumstance 
where a symbol for mud might be required that isn't covered by clay, silt or 
sand unless you are looking at fairly recently deposited material with a large 
organic component which might be better considered as 'flood debris' and 
possibly too ephemeral to mark on a map?

Just my thoughts.

Graham


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[Therion] view several caves in 3D (Philippe Vernant)

[Graham Mullan via Therion]

Phillipe Vernant said:

I have several caves in the same area, and I would like to see them all in 3D. 
I have a .th file that have the links to all the cave.th and so I can compile 
to get the 3D model of all the caves, but, can I compile each cave 
independently and then join them all up in one 3D viewer, loch for example ? 
I’d like to pick the ones I want to see in 3D and not to have to recompile each 
time.

Hi Phil

An output file cannot as far as I am aware simply be combined with another 
output file which I think is what you are asking. You can produce different 
output files showing different caves by using 'select' commands in your 
thconfig file and choosing which ones you want to output at any one time But 
adding one .lox file to another or one .3d file to another post compilation, 
not possible I think.

Graham

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[Therion] combining several lox files

[Graham Mullan via Therion]

Benedikt Hallinger said:

" the last problem now is, that the surface lox is in a different coordinate 
system than the caves (EPSG:31468 vs. lat-long) :/ I hoped loch would recognize 
this and recalculate as appropriate, but that was not the case. Is there some 
option to convert conveniently?"

I have never used Lat/Long but I do have a quite extensive data set that uses 
two different EPSG numbers, one UTM - and I think there's an IOS or two in 
there somewhere but cannot find them quickly - and this has generated a lox 
file that seems to have put everything in the right places. I have only ever 
seen "computer says no" messages when there have been sections where the 
co-ordinate system had not been specified at all.

I'd be wary about stating the cs in your thconfig file as that will clash if a 
different cs has been used elsewhere in the data set, I think.

Graham

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