[Therion] ***UNCHECKED*** RE: scrap without stations keeps the original sketch in Topodroid

[Bruce Mutton]

Omri, Alastair

I would have thought it almost impossible to draw a whole cave without any
point stations in the th2 files, but yesterday a colleague who just
self-taught themselves Therion presented me with a 5km long cave that has no
point stations defined in the th2 (it has survey stations of course, just
not drawn in the scraps).  It is also one of the better looking Therion maps
I have come across.  I have yet to pick it apart to see why it works and
what the implications are.

My suspicion is that it does not properly morph the sketches to the survey
network.

 

In response to Omri’s question – if your survey is perfect, and the field
sketch as well, then of course an unmorphed drawing will be just fine.  If
you have a real survey and sketch, subject to distortions due to loop
closures over multiple trips (multiple files), then the loops will not
match, and the drawing will need to be morphed due to loop closures and due
to scrap joins where the scraps are in different files or different
locations in the same file.

 

If, when using Topodroid, as I have seen people over here do, you accumulate
all of your survey trips in a single file, and end up with one huge sketch
for the cave, in which you manually compensate for any misclosures, then
Therion has nothing much left to do.  In that case, it might be fine to do
as you describe.  Until someone finds the next big breakthrough passage,
then it may or may not be.

 

Bruce

 

 

 

From: Therion <therion-bounces at speleo.sk> On Behalf Of alastair gott
Sent: Monday, 7 October 2019 19:34
To: List for Therion users <therion at speleo.sk>
Subject: Re: [Therion] scrap without stations keeps the original sketch in
Topodroid

 

Hi Omri,

 

You cannot have a scrap without any survey points in it. each scrap or th2
file needs 2 or greater survey stations in it to function correctly without
warping the image.

 

extended elevations are a bit different (and sometimes need careful
adjustment of the legs to fold the extended elevation in the correct way).

 

[Caviat, I know you can have a th2 file with no survey stations in it, but
we're not creating rocks today wookware.org/surveys/therion/testrocks].

 

 

Regards,
Alastair Gott.

AlastairGott at hotmail.com <mailto:AlastairGott at hotmail.com> ,
M: 07931779380.

  _____  

From: Therion <therion-bounces at speleo.sk <mailto:therion-bounces at speleo.sk>
> on behalf of עמרי גסטר <omrigas at gmail.com <mailto:omrigas at gmail.com> >
Sent: 06 October 2019 20:31
To: List for Therion users <therion at speleo.sk <mailto:therion at speleo.sk> >
Subject: [Therion] scrap without stations keeps the original sketch in
Topodroid 

 

Hi all, 

I want to raise a question I've been having with my self...

when I'm in the cave I use Topodroid to make the sketch. when I export the
map in Therion with "debug on" I see the changes that Therion makes which
make the final map different from the sketch I made in Topodroid (sometimes
it is a big difference).

a few days ago I noticed that if I make a new scrap and move all the map
elements that I draw except the stations, the map turns out exactly as I
draw it on Topodroid.

 

As I understand it, Therion change the map to overcome or compensate errors
or Deviations, especially when there are loops involved, but wouldn't it be
more accurate to stick to the original sketch that I drew with Topodroid  in
the cave?

what do you think?

 

Omri Gaster

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