here is a short mail exchange with bruce about "extend"

i played a little with the extend command. there are many variations (1 and 2 are stations)
- placing it before the data or after them
- "extend ??? 1 2" or "extend ??? 2 1"
- with an "extend ???" in the data or not
- combining with "extend ??? 1"

not considering the variations on the theme when there are crossways and loops

and the interaction with "flip horizontal"

maybe someone with plenty of time (and patience) will go thru the analysis of how therion handles these commands . . .

personally i use "absolute" extends the data. and it's been years now since i used "flip" (in therion).

we moved from lrud to splay.
what about going from L/R to fractional extend (including nil to break loops) ?

marco

---------- Forwarded message ---------
From: Bruce Mutton <bruce@tomo.co.nz>
Date: Wed, May 2, 2018, 21:48
Subject: Extended elevation discussion
To: Marco Corvi <marco.corvi@gmail.com>


Hi Marco

Glad you are spending time caving.  And is good to be disconnected sometimes!

 

Yes, extend is mysterious.  Your commentary is insightful and appreciated.

  1. Separating extend data from survey data:   choice will depend on what is important to the map author.
    Advantages = like information is kept together, dissimilar information is kept separate; able to have many different extend elevation shapes for one survey. 
    Disadvantages = you have duplication of survey leg enumeration for each extended elevation.  Sometimes every leg needs to be duplicated, but sometimes only at changes of extend ‘state’, so duplication can either be minimal or extensive, depending on the project.

    Enumerating extend stations and legs in the opposite direction (2 1) to what they are enumerated in the survey data (1 2) is usually OK. It often requires more explicit enumeration than if both progress in the same direction.  I have done it a number of times.  Sometimes ignores will only work in one direction, as I noted in the web page.

 

  1. Yes, I think extend left/right may behave like revise, I have thought that.  Pretty sure I have had cases where I have conflicting directions on the same leg, and the last one read will take precedence.  I tend to weed these out, as extend is unpredictable enough without leaving such things in the data!

 

  1. Flip and left right normal reverse: Good point, I had not thought of that.  However, I am always explicitly left and right myself.  While I have had some issues with flip, I don’t expect they are related to explicit extend directions.  What I do suspect is that some symbol alignments to not respond well to flip, and I suspect that implied joins of scraps (where line end points are snapped together within the same file) might tend to wreck flipped scraps.  That would be obviously user error if one scrap is flipped but not the other. The attached example from a few years ago shows what can happen if scraps are flipped.  I should go back and see if both scraps where flipped or only one!

 

This conversation might be useful to have on the forum.

Feel free to forward it to the forum if you like.

 

Bruce

 

From: Marco Corvi <marco.corvi@gmail.com>
Sent: Wednesday, 2 May 2018 11:05 PM
To: Bruce Mutton <bruce@tomo.co.nz>
Subject: Re: Extended elevation page

 

hi bruce,

 

sorry for the late answer;

i was off caving in an area with no connection.

 

i looked at the extend page.

that''s fine with me.

recently i have been just following therion news, without spending much time to check out things with examples, except in a few cases.

 

about extend:

 

1) i think it's not a good idea to separate leg data from leg extend, because you have to write the leg "name" (the stations) twice.

what happen if you have "1 2" with data and "2 1" with extend ? i do not know, i have to check when i get home.

 

2) i think that the syntax "extend right 1 2", might be a sort of revise, ie, it overrides the previous value. again i have to check this too

 

3) normal/reverse may be better than left/right, when you use flip

 

that said i tend to use absolute extend (left/right), but maybe it's time that i go relative.

 

extend is a diffucult topic, and your page is a good idea. there are many different situations for "extend"; you may add the examples in subpages.

 

marco

 

On Mon, Apr 30, 2018, 12:25 Bruce Mutton <bruce@tomo.co.nz> wrote:

Hi Marco

I sent this message to the Therion forum a few hours ago, and have not received a mail back yet, so I am wondering if it is broken in some way, I notice the website has been responding very slowly all day.  However I could edit the wiki just fine. 

Anyway, reason for this email is to let you know about the new Extended Elevations page, and checking that you are happy with what I have written, and references to your altervista pages. 

And perhaps you have further insights into extended elevations! 

Hope you are well.

Regards

Bruce Mutton 

From: Bruce Mutton <bruce@tomo.co.nz>
Sent: Monday, 30 April 2018 6:01 PM
To: 'List for Therion users' <therion@speleo.sk>
Subject: Extended elevation page 

Good morning all

I have just put together a Therion Extended Elevations page, having convinced myself that I have almost figured out how to make them work.  You can navigate there from the wiki start page, via the ‘Data Organisation’ link. 

Thanks and apologies to Marco Corvi, for the inspiration and words I have borrowed from his page.  Marco, is it OK? 

It is not quite complete yet (I have a history of not completing projects) however if someone can direct me to the centreline and drawing data for the famous Therion Extended Elevation Control sample, then I might remain inspired enough to generate a more comprehensive set of examples. 

Enjoy your caves

Bruce