Exporting to Survex for passage tubes viewing

[Olly Betts]

On Thu, Jan 20, 2022 at 07:26:21PM -0500, Luc Le Blanc wrote:
> An Auriga user tells me the SVX files exported by Auriga do not allow
> viewing passages tubes. Another cave fiddled with his data and
> returned a tube-capable SVX file. When I compare both SVX files, I see
> each shot line (data normal) is now followed by more than another
> passage dimensions (data passage) line, providing the passage
> dimensions at a station that is not part of the current survey shot,
> but that is connected to the dimension-bearing station of the current
> shot.
> 
> Question: in the example below, if station 1 was also connected to,
> say, station 4, that happened to bear passage dimensions too, should
> we have another data passage line for station 4 after those two?
> 
> *data normal from to length compass  clino
>             0             1      4.05   109.9       1.0
> *data passage station left right up down
>             1    0.86    0.00    0.82    0.28
>             2    0.00    0.91    1.44    0.10

The documentation for the `PASSAGE` data style seems to answer all the
questions you ask above:

        PASSAGE
                This survey style defines a 3D "tube" modelling a
                passage in the cave. The tube uses the survey
                stations listed in the order listed. It's
                permitted to use survey stations which aren't
                directly linked by the centre-line survey. This
                can be useful - sometimes the centreline will step
                sideways or up/down to allow a better sight for
                the next leg and you can ignore the extra station.
                You can also define tubes along unsurveyed
                passages, akin to "nosurvey" legs in the
                centreline data.

                This means that you need to split off side
                passages into separate tubes, and hence separate
                sections of passage data, starting with a new
                *data command.

                Simple example of how to use this data style (note
                the use of ignoreall to allow a free-form text
                description to be given):

    *data passage station left right up down ignoreall
    1  0.1 2.3 8.0 1.4  Sticking out point on left wall
    2  0.0 1.9 9.0 0.5  Point on left wall
    3  1.0 0.7 9.0 0.8  Highest point of boulder

                Each *data passage data block describes a single
                continuous tube - to break a tube or to enter a
                side passage you need to have a second block. With
                Survex 1.2.30 and older, you had to repeat the
                entire *data passage line to start a new tube, but
                in Survex 1.2.31 and later, you can just use *data
                without any arguments.

                For example here the main passage is 1-2-3 and a
                side passage is 2-4:

    *data passage station left right up down ignoreall
    1  0.1 2.3 8.0 1.4  Sticking out point on left wall
    2  0.0 1.9 9.0 0.5  Point on left wall opposite side passage
    3  1.0 0.7 9.0 0.8  Highest point of boulder
    ; If you're happy to require Survex 1.2.31 or later, you can just use
    ; "*data" here instead.
    *data passage station left right up down ignoreall
    2  0.3 0.2 9.0 0.5
    4  0.0 0.5 6.5 1.5  Fossil on left wall

On Mon, Jan 31, 2022 at 02:40:28PM -0500, Luc Le Blanc wrote:
> * is placing passage dimensions after each survey shot in the SVX file
> a requirement, or is the quoted behavior a mistake?

A `*data passage` after each shot sounds like a bad idea to me - you'd
end up having to repeat the dimensions of each station (except for
those at a dead end or entrance).

> * are splay measures used to build the tubular view? (it seems they aren't)

No.  Given the rise of disto-based surveying, it certainly would be nice
to create passage skins from splays automatically.  I don't think it
would make sense to force this into the rectangular cross-section tube
model though - `*data passage` really just attempts to provide a useful
way to represent data from LRUD measurements.  Skins from splays would
probably happen in Aven.

> * when activating the tubular view, I get very long ghost lines that
> do not correspond to any survey shot - could this be a loop-related
> bug?

As per the docs, each `*data passage` block is a continuous tube - your
"long ghost lines" are presumably because your data tells Survex that
the tube continues into what's actually an entirely different passage.

Cheers,
    Olly