Re: [Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

>> Extend  in Therion is the same as the way PocketTopo implements 
>> 'flip' (equivalent to Therion's 'extend').

More precisely equivalent to Therion's 'extend reverse'.

And my experience is that it is very confusing having it 'pivot on the station 
previous' in a graphical interface (PocketTopo) but it is quite OK in a textual 
interface (Therion).

I am quite comfortable with the way Therion does it, but if I were designing a 
graphical interface I would have it 'pivot about the selected station' instead 
(although this would be problematic if one were to want to individually extend 
splay shots in different directions).

Pivoting with a single station selection always seems imprecise to me, because 
there is no clear indication of which way the extended centreline is expected 
to be (let alone actually) propagating from (unless it is a splay shot). 

 

> Interesting. So we have three existing implementations, but two different 
> mechanisms (Survex does it the other way). Most of Therion's data syntax is 
> compatible (and directly interchangeable) with Survex.

> This is an unusual case where it isn't compatible.

 

I wonder what TopoDroid does? 

 

Bruce

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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

> Pretty sure this is the way it is.  Which is why I tend to use extend  
> rather than with a single .

Yes, I think this might be something I will end up relying on, because
it is much more readable, and understandable. And on top of that, you
know that even if Therion gets changed to follow Survex, at least your
Therion data will work either way.

> Extend  in Therion is the same as the way PocketTopo implements 
> 'flip' (equivalent to Therion's 'extend').

Interesting. So we have three existing implementations, but two
different mechanisms (Survex does it the other way). Most of Therion's
data syntax is compatible (and directly interchangeable) with Survex.
This is an unusual case where it isn't compatible.
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

Tarquin, our messages crossed...

> At least in my head, "extend vertical 3" feels like it should mean 
> "everything from station 3 onwards". I think Bruce also expected this, given 
> what he wrote in the wiki "extend" article:
https://therion.speleo.sk/wiki/extend
"Usually this option will not work as described, unless it is preceded by one 
or two extend right  statements."

No, I did not intend it that way, but I did not write it very clearly, as I 
noticed when I sent my previous message.

The bit about 'usually will not work' is probably another issue.  I don't know 
if it will still be the case with the recent changes.

Bruce

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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

On 20/12/2019 20:58, Tarquin Wilton-Jones via Therion wrote:
>> If extend algorithm follows stations in order 1 - 2 - 3 - 4 - 5 - 6 - 7
>> - 8 - 9 and you specify
>> extend vertical 3
>> extend right 8
>> Then stations 3,4,5,6,7 should be placed vertical and 8,9 on the right.
>> I have tested it and in my example, it works like this.
> 
> In the case of what you said, I would have expected the following legs
> to be default (right):
> 
> 1-2
> 2-3
> 
> the following legs to be vertical:
> 
> 3-4
> 4-5
> 5-6
> 6-7
> 7-8
> 
> then the following legs to be right:
> 
> 8-9
> 
> Instead, leg 2-3 will be vertical, and leg 7-8 will be right.
> 
> At least in my head, "extend vertical 3" feels like it should mean
> "everything from station 3 onwards". I think Bruce also expected this,
> given what he wrote in the wiki "extend" article:
> https://therion.speleo.sk/wiki/extend
> "Usually this option will not work as described, unless it is preceded
> by one or two extend right  statements."
> 
> So perhaps this is either a generic misunderstanding; Therion assumes
> that by  it means . We
> assume that by  it should be  station>.
> 
> I don't know which of those is right. I have also never used this with
> Survex, so I don't know if Survex agrees with Therion - Perhaps Wookey
> can say?

Survex agrees with me. Therion does not.

1 2 20 0 -80
2 3 5 62 -10
3 4 5 12 -15
4 5 5 132 17
5 6 5 18 -15
6 7 5 201 -7
7 8 5 63 -10
8 9 20 0 -80
9 10 5 15 -45
10 11 5 357 -30
11 12 5 27 -25
12 13 5 290 -18
13 14 5 323 -22
14 15 5 300 -7
15 16 5 15 -35
16 17 5 337 -42
17 18 5 281 -38
18 19 5 225 -20
19 20 20 0 -80

Therion:
extend start 1
extend left 3
extend right 8
export map -proj extended -o "somepitches.pdf"

Survex specfile:
*start somepitches.1
*eleft somepitches.3
*eright somepitches.8
extend.exe --specfile=extend.svx somepitches.3d somepitches_extended.3d

I have attached the two outputs. You can see that they are not the same.


somepitches.pdf
Description: Adobe PDF document


somepitches_extended.3d
Description: Binary data
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

>but now I am wondering ... if they are supposed to take place for "the leg 
>that reaches this station, and every leg after it".
... o_O

Pretty sure this is the way it is.  Which is why I tend to use extend  
rather than with a single .  It is more easily understood six months 
later when you try to figure out what is going on. But there is good reason to 
use extend with  as well - auto propagation of the extend direction.
Extend  in Therion is the same as the way PocketTopo implements 'flip' 
(equivalent to Therion's 'extend').  Except that with PocketTopo you do it 
interactively in the graphic view, and with Therion textually.

Bruce

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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

> If extend algorithm follows stations in order 1 - 2 - 3 - 4 - 5 - 6 - 7
> - 8 - 9 and you specify
> extend vertical 3
> extend right 8
> Then stations 3,4,5,6,7 should be placed vertical and 8,9 on the right.
> I have tested it and in my example, it works like this.

In the case of what you said, I would have expected the following legs
to be default (right):

1-2
2-3

the following legs to be vertical:

3-4
4-5
5-6
6-7
7-8

then the following legs to be right:

8-9

Instead, leg 2-3 will be vertical, and leg 7-8 will be right.

At least in my head, "extend vertical 3" feels like it should mean
"everything from station 3 onwards". I think Bruce also expected this,
given what he wrote in the wiki "extend" article:
https://therion.speleo.sk/wiki/extend
"Usually this option will not work as described, unless it is preceded
by one or two extend right  statements."

So perhaps this is either a generic misunderstanding; Therion assumes
that by  it means . We
assume that by  it should be .

I don't know which of those is right. I have also never used this with
Survex, so I don't know if Survex agrees with Therion - Perhaps Wookey
can say?
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Stacho Mudrak]

Hi Tarquin,

I am afraid, I do not understand your problem.

If extend algorithm follows stations in order 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8
- 9 and you specify
extend vertical 3
extend right 8
Then stations 3,4,5,6,7 should be placed vertical and 8,9 on the right. I
have tested it and in my example, it works like this.

Could you please illustrate, what's wrong?

Thanks, S.





On Fri, 20 Dec 2019 at 20:02, Tarquin Wilton-Jones via Therion <
therion@speleo.sk> wrote:

> Stacho,
>
> I am wondering if there is a fault in all the other "extend" options,
> rather than this problem being specific to "extend ignore".
>
> extend vertical 3 # everything after station *2* is vertical
> extend right 8 # everything after station *7* is extended to the right
>
> It seems like your "extend ignore" fix did not change any of these
> others, but now I am wondering if this is a general bug, or if they are
> supposed to take place for "the leg that reaches this station, and every
> leg after it".
>
> ... o_O
>
> Cheers,
>
> Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

Stacho,

I am wondering if there is a fault in all the other "extend" options,
rather than this problem being specific to "extend ignore".

extend vertical 3 # everything after station *2* is vertical
extend right 8 # everything after station *7* is extended to the right

It seems like your "extend ignore" fix did not change any of these
others, but now I am wondering if this is a general bug, or if they are
supposed to take place for "the leg that reaches this station, and every
leg after it".

... o_O

Cheers,

Tarquin
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[Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

Indeed, thanks.
I will play and report in due course.  I will be interested to learn how the 
log reports your examples in https://therion.speleo.sk/wiki/breakingextend 
Tarquin.
I ran some larger projects this morning, and got some log transcripts that were 
not as I would have expected.  I need to study the behaviour with some small 
projects and check the behaviour leg by leg.  
I have a lot of BACK extends, which do not necessarily match any of the extend 
options, and multiple STARTs and the odd extend to unnamed stations.
I guess this is why I wanted the logging, so I could learn exactly what is 
going on, so that I can then make good decisions. 
Cheers
Bruce

-Original Message-
From: Therion  On Behalf Of Tarquin Wilton-Jones via 
Therion
Sent: Wednesday, 4 December 2019 08:55
To: therion@speleo.sk
Cc: Tarquin Wilton-Jones 
Subject: Re: [Therion] Breaking a loop at a specific station on extended 
elevation

> I have added
> 
> log extend
> 
> feature to thconfig. It should log the traversing sequence of extend 
> algorithm to therion.log file.

Brilliant! Thanks Stacho :)

I will add it to my wiki article. (And I have no doubt that Bruce will also add 
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

> I have added
> 
> log extend
> 
> feature to thconfig. It should log the traversing sequence of extend
> algorithm to therion.log file.

Brilliant! Thanks Stacho :)

I will add it to my wiki article. (And I have no doubt that Bruce will
also add it to his.)
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Stacho Mudrak]

Hi Bruce,

I have added

log extend

feature to thconfig. It should log the traversing sequence of extend
algorithm to therion.log file.

HTH, S.

On Thu, 14 Nov 2019 at 19:29, Bruce Mutton  wrote:

> Thanks Stacho,
>
> I have had a look through my projects, and I don’t think I have ever used
> an ‘extend ignore station’ because of its unpredictable results (but I have
> used many ‘extend ignore leg’, which usually work as expected).  A quick
> check seems to indicate all my projects are unaffected by your latest
> update 094ac85fc5.
>
>
>
> Having a play with Tarquin’s example, it looks like an effect of ‘extend
> ignore station’ is to cause the map-connection break to occur at that
> station.  That is conceptually quite nice for users.  It seems to be
> consistent in that behaviour for the simple example, and is only
> ineffective if the station chosen is not in a loop (as you might expect). I
> did not test it where there is a pair of open branches though – that is a
> common scenario that should be checked.
>
>
>
> One more wish list for extend.  I would like a;
>
>
>
> debug extend
>
>
>
> statement.  This would enumerate in the log file the sequence of
> stations/legs that the extend algorithm is traversing.  In complex survey
> networks with many loops it can seem impossible to unravel a sensible
> extended centreline.  For example, if there are six survey branches coming
> into a single station, how do you isolate the particular leg that you
> want?  A textual debug might help find the answer.
>
>
>
> Bruce
>
>
>
>
>
> *From:* Therion  *On Behalf Of *Stacho Mudrak
> *Sent:* Friday, 15 November 2019 00:09
> *To:* List for Therion users 
> *Subject:* Re: [Therion] Breaking a loop at a specific station on
> extended elevation
>
>
>
> Normally,
>
>
>
> extend ignore 6
>
>
>
> should do the job. But there was a bug in the code, so it did not work as
> intended.
>
>
>
> It should be fixed now in the latest commit. If some of you have more
> complex entended elevation projects, could you please check, whether this
> change does not introduce new errors?
>
> The behaviour of "extend ignore  " should not be affected.
>
>
>
> Thanks, S.
>
>
>
> On Sun, 10 Nov 2019 at 12:08, Tarquin Wilton-Jones via Therion <
> therion@speleo.sk> wrote:
>
> What can I say?!
>
> Bruce, that was some black magic. I don't quite understand why asking it
> to ignore a leg then changing your mind and asking it to draw it anyway,
> would cause it to then split it at the point you want. I wonder if I
> will be able to make sense out of that in future.
>
> What is makes me wonder is; why doesn't this exist?
> extend break 6
>
> This could cause a centreline "weakness", and prefer (but not mandate)
> breaking at that point. It would massively simplify this control, and be
> much more predictable.
>
> > try to change the line in your .th file from:
> >
> > extend ignore 6 5
> >
> > to:
> >
> > extend ignore 5 6
> >
> > There is no leg 6-5 in your data, but there is leg 5-6.
>
>
> This does not work. I assume that is because it is trying to extend the
> centreline from left to right, so it steps backwards through that oxbow
> (compared with the data). Or maybe I have not played with Bruce's
> solution enough...
>
> Cheers!
>
> Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Martin Sluka via Therion]

Thank you!

Martin

> 2. 12. 2019 v 9:22, Tarquin Wilton-Jones via Therion :
> 
>> This would make an excellent mini topic on the wiki (in the existing
>> article on "extend").
> 
> 
> I have now added a new article, with details of the investigation:
> https://therion.speleo.sk/wiki/breakingextend
> 
> Because it uses a load of images, it was nicer to have it as a separate
> article, rather than litter the existing one. Bruce, please double check
> you are happy with how I linked it from your "extend" article.
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

> This would make an excellent mini topic on the wiki (in the existing
> article on "extend").


I have now added a new article, with details of the investigation:
https://therion.speleo.sk/wiki/breakingextend

Because it uses a load of images, it was nicer to have it as a separate
article, rather than litter the existing one. Bruce, please double check
you are happy with how I linked it from your "extend" article.
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[Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

Thanks Stacho, 

I have had a look through my projects, and I don’t think I have ever used an 
‘extend ignore station’ because of its unpredictable results (but I have used 
many ‘extend ignore leg’, which usually work as expected).  A quick check seems 
to indicate all my projects are unaffected by your latest update 094ac85fc5.

 

Having a play with Tarquin’s example, it looks like an effect of ‘extend ignore 
station’ is to cause the map-connection break to occur at that station.  That 
is conceptually quite nice for users.  It seems to be consistent in that 
behaviour for the simple example, and is only ineffective if the station chosen 
is not in a loop (as you might expect). I did not test it where there is a pair 
of open branches though – that is a common scenario that should be checked.

 

One more wish list for extend.  I would like a;

 

debug extend

 

statement.  This would enumerate in the log file the sequence of stations/legs 
that the extend algorithm is traversing.  In complex survey networks with many 
loops it can seem impossible to unravel a sensible extended centreline.  For 
example, if there are six survey branches coming into a single station, how do 
you isolate the particular leg that you want?  A textual debug might help find 
the answer.

 

Bruce

 

 

From: Therion  On Behalf Of Stacho Mudrak
Sent: Friday, 15 November 2019 00:09
To: List for Therion users 
Subject: Re: [Therion] Breaking a loop at a specific station on extended 
elevation

 

Normally, 

 

extend ignore 6

 

should do the job. But there was a bug in the code, so it did not work as 
intended.

 

It should be fixed now in the latest commit. If some of you have more complex 
entended elevation projects, could you please check, whether this change does 
not introduce new errors?

The behaviour of "extend ignore  " should not be affected.

 

Thanks, S.

 

On Sun, 10 Nov 2019 at 12:08, Tarquin Wilton-Jones via Therion 
mailto:therion@speleo.sk> > wrote:

What can I say?!

Bruce, that was some black magic. I don't quite understand why asking it
to ignore a leg then changing your mind and asking it to draw it anyway,
would cause it to then split it at the point you want. I wonder if I
will be able to make sense out of that in future.

What is makes me wonder is; why doesn't this exist?
extend break 6

This could cause a centreline "weakness", and prefer (but not mandate)
breaking at that point. It would massively simplify this control, and be
much more predictable.

> try to change the line in your .th file from:
> 
> extend ignore 6 5
> 
> to:
> 
> extend ignore 5 6
> 
> There is no leg 6-5 in your data, but there is leg 5-6.


This does not work. I assume that is because it is trying to extend the
centreline from left to right, so it steps backwards through that oxbow
(compared with the data). Or maybe I have not played with Bruce's
solution enough...

Cheers!

Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

> Normally, 
> 
> extend ignore 6
> 
> should do the job. But there was a bug in the code, so it did not work
> as intended.


Thanks so much for this explanation! Suddenly everything makes sense,
once you know that it was unintentional behaviour :)

> It should be fixed now in the latest commit.


Awesome. In that case, I will use the dev release for writing the
article about this particular case.

Cheers,

Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Stacho Mudrak]

Normally,

extend ignore 6

should do the job. But there was a bug in the code, so it did not work as
intended.

It should be fixed now in the latest commit. If some of you have more
complex entended elevation projects, could you please check, whether this
change does not introduce new errors?
The behaviour of "extend ignore  " should not be affected.

Thanks, S.

On Sun, 10 Nov 2019 at 12:08, Tarquin Wilton-Jones via Therion <
therion@speleo.sk> wrote:

> What can I say?!
>
> Bruce, that was some black magic. I don't quite understand why asking it
> to ignore a leg then changing your mind and asking it to draw it anyway,
> would cause it to then split it at the point you want. I wonder if I
> will be able to make sense out of that in future.
>
> What is makes me wonder is; why doesn't this exist?
> extend break 6
>
> This could cause a centreline "weakness", and prefer (but not mandate)
> breaking at that point. It would massively simplify this control, and be
> much more predictable.
>
> > try to change the line in your .th file from:
> >
> > extend ignore 6 5
> >
> > to:
> >
> > extend ignore 5 6
> >
> > There is no leg 6-5 in your data, but there is leg 5-6.
>
>
> This does not work. I assume that is because it is trying to extend the
> centreline from left to right, so it steps backwards through that oxbow
> (compared with the data). Or maybe I have not played with Bruce's
> solution enough...
>
> Cheers!
>
> Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Martin Sluka via Therion]

12. 11. 2019 v 19:25, Bruce Mutton :
> 
> While I would welcome Therion improvement in this space, I am a little
> concerned about all of my existing extended elevations that might be broken
> by changes in behaviour.  I'm sure this eventuality can be accommodated by
> clever coders however.

There are three variants:

extend ignore 5 6
extend ignore 6 5
extend ignore 6

Each one generates different export, but only that one, which is the most not 
logic - extended ignore 5 6 - generates what is expected. 

Try to generate files for "extend ignore X” for X = 2, 3, 4, 5

If the Therion’s code will be corrected, there should be two variants anyway - 
first uncorrected for existing projects and another one (correct) for new 
projects. 

Martin

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[Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

Hi Wookey, Tarquin,
I agree that extended elevations are too unpredictable, hard to use, and
that there needs to be a simpler way.  Not sure if it is that there are
bugs, that instructions and understanding is inadequate, or if there is
required functionality that is missing.

Because extend ignore is usually associated with a survey network junction
(nearby or not so nearby), I have a gut feeling that specifying a leg
(perhaps with sensitivity to direction) will generally give more refined
control.  To use extend ignore to break at a particular station, using just
a single station (if I have it right), you need to specify the station one
leg beyond the desired break (a bit like 'flip' in PocketTopo).  Generally,
I find this approach to result in cognitive overload!  If you want the break
at a junction, you would often need to specify which leg anyway, depending
on whether Therion's auto extended generation was incoming to or outgoing
from the junction.

Extend ignore directly controls branching, and only indirectly controls the
break-point in the centreline.  So perhaps the issue is missing
functionality.  Do we need direct user control over the break stations?  It
would be nice.

Extend ignore also feels like a very indirect way of specifying network
generation.  As someone mentioned a long time back, it would be easier to
specify 'extend force ' rather than 'extend ignore '.   ie
'Specify take this leg, rather than specifying take a different leg'.
Especially where there are more than three branches emanating from a single
station.

While I would welcome Therion improvement in this space, I am a little
concerned about all of my existing extended elevations that might be broken
by changes in behaviour.  I'm sure this eventuality can be accommodated by
clever coders however.
:)
Bruce

-Original Message-
From: Therion  On Behalf Of Wookey
Sent: Tuesday, 12 November 2019 11:18
To: therion@speleo.sk
Subject: Re: [Therion] Breaking a loop at a specific station on extended
elevation

On 2019-11-12 07:20 +1300, Bruce Mutton wrote:

> I don't have a problem with the characteristic you mention in point 2.  I
think it is just semantics associated with the word 'ignore', and sequential
process.  If you think 'break' then is it all OK?

We think it should be possible to specify 'break/ignore' at a point, rather
than a point+direction (i.e. a leg/pair of points)
We want the computer to worry about the 'direction' aspect, and feel we
shouldn't have to. It seems like this should be possible.

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

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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Wookey]

On 2019-11-12 07:20 +1300, Bruce Mutton wrote:

> I don't have a problem with the characteristic you mention in point 2.  I 
> think it is just semantics associated with the word 'ignore', and sequential 
> process.  If you think 'break' then is it all OK?

We think it should be possible to specify 'break/ignore' at a point, rather
than a point+direction (i.e. a leg/pair of points)

We want the computer to worry about the 'direction' aspect, and feel
we shouldn't have to. It seems like this should be possible.

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


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[Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

Tarquin
Was hoping you would offer!
Yes, this simple example makes a great starting point for an example that can 
shine light on extended elevation behaviour, and can be made progressively more 
complex to demonstrate behaviour changes.

I have in previous projects noticed all you mention in your point 1 below.
I don't have a problem with the characteristic you mention in point 2.  I think 
it is just semantics associated with the word 'ignore', and sequential process. 
 If you think 'break' then is it all OK?
Bruce

-Original Message-
From: Therion  On Behalf Of Tarquin Wilton-Jones via 
Therion
Sent: Monday, 11 November 2019 21:42
To: therion@speleo.sk
Cc: Tarquin Wilton-Jones 
Subject: Re: [Therion] Breaking a loop at a specific station on extended 
elevation

Hi Bruce,

> Stepping through the process I take;


Thanks for that detailed explanation!

The main things that threw me were:

1. That Therion is stepping *backwards* along the oxbow - in the direction of 
the cave passage from the "start" instead of in the direction that it is 
surveyed. This means that you must use your "extend ignore" in that same 
direction. "extend ignore 6 5" works, "extend ignore 5 6" does not. Apparently 
I am not the only one who finds this surprising. Also, just to be confusing, 
"extend ignore 6" will cause it to go completely wrong and break both ends of 
the loop (sounds buggy to me), while if the loops had more stations, it would 
break at station *2* in the oxbow, rather than at station 6. In loops with more 
stations, you can also break the offending leg in both directions without harm, 
while in the data I gave you, you can't. So there are some real gotchas in here.

2. That you can then tell a leg that was ignored to not be ignored after all. 
It can have two states specified, one immediately after the other, and *both* 
are respected. The first makes Therion change its "main path"
of the extended elevation, and the second makes it draw the parts of the 
disconnected passage in the desired direction.

This would make an excellent mini topic on the wiki (in the existing article on 
"extend"). I have made a more complete version of the survey that allows it to 
show a couple more variations. So if you don't mind, I would like to use some 
of your words to turn it into a mini-topic.
Unless you argue, I will start to write this up.

Cheers again, and thanks for the wisdom.

Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

Hi Bruce,

> Stepping through the process I take;


Thanks for that detailed explanation!

The main things that threw me were:

1. That Therion is stepping *backwards* along the oxbow - in the
direction of the cave passage from the "start" instead of in the
direction that it is surveyed. This means that you must use your "extend
ignore" in that same direction. "extend ignore 6 5" works, "extend
ignore 5 6" does not. Apparently I am not the only one who finds this
surprising. Also, just to be confusing, "extend ignore 6" will cause it
to go completely wrong and break both ends of the loop (sounds buggy to
me), while if the loops had more stations, it would break at station *2*
in the oxbow, rather than at station 6. In loops with more stations, you
can also break the offending leg in both directions without harm, while
in the data I gave you, you can't. So there are some real gotchas in here.

2. That you can then tell a leg that was ignored to not be ignored after
all. It can have two states specified, one immediately after the other,
and *both* are respected. The first makes Therion change its "main path"
of the extended elevation, and the second makes it draw the parts of the
disconnected passage in the desired direction.

This would make an excellent mini topic on the wiki (in the existing
article on "extend"). I have made a more complete version of the survey
that allows it to show a couple more variations. So if you don't mind, I
would like to use some of your words to turn it into a mini-topic.
Unless you argue, I will start to write this up.

Cheers again, and thanks for the wisdom.

Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

Hi Tarquin

 

> I don't quite understand why asking it to ignore a leg then changing your 
> mind and asking it to draw it anyway, would cause it to then split it at the 
> point you want. I wonder if I will be able to make sense out of that in 
> future.

 

I think of extended generation as a trial and error sequential process.  

Tell it where to start, then what direction.  See what happens.

At the point where the generation deviates from what you would like, add an 
instruction, in the correct sequence.  See what happens.

Once that part works OK, look further along the centreline to find the next 
deviation, and add another instruction.  

So it is not changing mind or contradicting previous statements.  See sequence 
below.

 

>What is makes me wonder is; why doesn't this exist?

>extend break 6

>This could cause a centreline "weakness", and prefer (but not mandate) 
>breaking at that point. It would massively simplify this control, and be much 
>more predictable.

 

This is pretty much exactly what ‘extend ignore 6 ’ does.  It causes the centreline to break at station 6, and continue 
automatic extended centreline generation elsewhere.

 

Here is the plan view, and the solution I came up with.  There are probably 
others.



survey extendedloop

  centreline

data normal from to length compass clino

1  2  1  0  5

2  3  1  0  -5

3  4  1  45  -10

4  5  1  90  5

5  6  1.71  225  45

6  2  1.71  225  -45

5  7  1  90  0



 extend start 1

 extend right 1

 extend ignore 6 5

 extend right 6 5

  endcentreline

endsurvey

 

Stepping through the process I take;

 extend start 1

 extend right 1

This produces an extended centreline that propagates 1 2 6 5 4 3 2, and now 
that the loop is closed (and broken at 2), propagation continues for the rest 
of the cave from 5 7.



Could I have predicted this sequence?  No.  Usually I think Therion chooses the 
surveyed sequence, but not always.  This is why I use a trial and error 
approach.

>From the diagram above, I think that I want the map-connection line  (the 
>break) at station 6, and the extended generation direction for the leg to 
>ignore is 6 5 (despite the survey data enumerating this leg as 5 6).  So now I 
>try;

 

 extend start 1

 extend right 1

 extend ignore 6 5



This is much better, but the leg 5 6 is extending right and not left.

The apparent generation sequence is now 1 2 6, 2 3 4 5 6, 5 7

So I could try;

 extend right 6 5

or

 extend left 5 6

I chose the former because it involved less typing, but the latter makes more 
sense perhaps if you are following the apparent sequence of generation.  It 
turns out that they both work, and produce this (same apparent generation 
sequence, just the extend direction differs for 5 6);



 

Don’t worry, extend is a mystery for me as well.

This example turns out to fairly straight forward, but it can be very 
complicated for a real cave, especially if you don’t start thinking about the 
extended elevation until you have 10 km of passage in your project.

 

Any further insights greatly appreciated.

 

Bruce

 

PS:  I just noticed on page 25 of the Therion Book, that extend directions can 
be explicitly influenced from within a scrap drawing.



I’d be interested in finding out about usage scenarios.

 

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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Martin Sluka via Therion]

> 10. 11. 2019 v 12:07, Tarquin Wilton-Jones via Therion :
> 
> This does not work. 

You are right. It is very strange it break centreline in station 2 and not in 
station 5 or 6.

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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

What can I say?!

Bruce, that was some black magic. I don't quite understand why asking it
to ignore a leg then changing your mind and asking it to draw it anyway,
would cause it to then split it at the point you want. I wonder if I
will be able to make sense out of that in future.

What is makes me wonder is; why doesn't this exist?
extend break 6

This could cause a centreline "weakness", and prefer (but not mandate)
breaking at that point. It would massively simplify this control, and be
much more predictable.

> try to change the line in your .th file from:
> 
> extend ignore 6 5
> 
> to:
> 
> extend ignore 5 6
> 
> There is no leg 6-5 in your data, but there is leg 5-6.


This does not work. I assume that is because it is trying to extend the
centreline from left to right, so it steps backwards through that oxbow
(compared with the data). Or maybe I have not played with Bruce's
solution enough...

Cheers!

Tarquin
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Martin Sluka via Therion]

9. 11. 2019 v 20:46, Bruce Mutton :Can someone please tell us the magic formula of extend commands that will produce the desired output?Hi Tarquin,try to change the line in your .th file from:extend ignore 6 5to:extend ignore 5 6There is no leg 6-5 in your data, but there is leg 5-6.Martin

extendedloopEXT.pdf
Description: Adobe PDF document
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Re: [Therion] Breaking a loop at a specific station on extended elevation

[Bruce Mutton]

Like this?



I find extend very trial and error.  I looked at your file and looked at my 
wiki page, and decided it might not be easily possible.  Then I tried it out, 
and on my second attempt made it work.  This does not necessarily mean it will 
work as part of a large project however!!

https://therion.speleo.sk/wiki/extend#summary_of_all_extend_options_for_survey_centrelines

Bruce

 

 

-Original Message-
From: Therion  On Behalf Of Tarquin Wilton-Jones via 
Therion
Sent: Sunday, 10 November 2019 01:46
To: therion@speleo.sk
Cc: Tarquin Wilton-Jones 
Subject: [Therion] Breaking a loop at a specific station on extended elevation

 

Hi folks,

 

There are a few of us who are struggling with an extended elevation problem. I 
have attached a sample data file, which represents the data from a real cave.

 

There is a main passage (stations 1-2-3-4-5-7), and a high level oxbow 
(stations 2-6-5). Because the oxbow is shorter, Therion defaults to using that 
as the primary extended elevation path, which is not desired.

The natural (human preferred) way of extending that, is to show the main 
passage as a single line, then have the high level oxbow split at station 6, 
with a leg pointing to each of the two stations it connects to, and a dotted 
line connecting the two versions of station 6. Like this (if your email client 
shows this with a fixed width font):

 

 66

/  \

1--2--3--4--5--7

 

We tried various "extend left" "extend right" and "extend ignore", and we 
managed to make it break station 2, but it seems not to want to break on 
station 6. (We can obviously break it in the right place by breaking the data, 
but that is not the intention is to keep the data valid.)

 

Can someone please tell us the magic formula of extend commands that will 
produce the desired output?

 

Thanks for the assistance.

 

Tarquin



extendedloop-rbm.th
Description: Binary data
encoding  utf-8
source extendedloop-rbm.th

select extendedloop

export model -output extendedloop.3d
export map -proj plan -output extendedloopPLAN.pdf -layout-debug station-names
export map -proj extended -output extendedloopEXT.pdf -layout-debug 
station-names
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[Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones via Therion]

Hi folks,

There are a few of us who are struggling with an extended elevation
problem. I have attached a sample data file, which represents the data
from a real cave.

There is a main passage (stations 1-2-3-4-5-7), and a high level oxbow
(stations 2-6-5). Because the oxbow is shorter, Therion defaults to
using that as the primary extended elevation path, which is not desired.
The natural (human preferred) way of extending that, is to show the main
passage as a single line, then have the high level oxbow split at
station 6, with a leg pointing to each of the two stations it connects
to, and a dotted line connecting the two versions of station 6. Like
this (if your email client shows this with a fixed width font):

 66
/  \
1--2--3--4--5--7

We tried various "extend left" "extend right" and "extend ignore", and
we managed to make it break station 2, but it seems not to want to break
on station 6. (We can obviously break it in the right place by breaking
the data, but that is not the intention is to keep the data valid.)

Can someone please tell us the magic formula of extend commands that
will produce the desired output?

Thanks for the assistance.

Tarquin
encoding  utf-8

survey extendedloop

  centreline

extend start 1

data normal from to length compass clino

1  2  1  0  0
2  3  1  0  0
3  4  1  45  0
4  5  1  90  0
5  6  1.71  225  45
6  2  1.71  225  -45
5  7  1  90  0

  endcentreline

endsurvey
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