Passage walls in Survex

[Olly Betts]

On Wed, Feb 25, 2009 at 02:15:37PM +0000, Footleg wrote:
> Talking of the passage walls feature, by which I mean the handling of
> LRUD data. In all the other programs I have played with, the LRUD data
> is associated with a station in a leg, except Survex which associates
> it with just a station.

That's not correct - it's associated with a station, but in the order,
direction, and orientation described by the passage data.

Here's what the manual says:

    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 seperate
    tubes, and hence separate sections of passage data, starting with a new
    *data command.

> This does not make sense to me, as the LRUD
> data needs to be expressed in the context of a survey leg to define
> the plane of the passage cross section which the LRUD data is measured
> against. For example at a station at a 3 way junction you need to know
> which pair of legs the LRUD data relates to.

If you want to simply process LRUD specified at every sequential station in a
survey, just enter it in that order.  Which legs it relates to is clear from
the stations on the line before and after in the passage data (OK, there's the
case where there is more than one leg between the same two stations, but in
reality it's not useful to distinguish between such legs).

> So I would propose
> supporting LRUD data attached to a leg. By default take it to be for
> the first station in the leg, but allow an option to specify it for
> the second station in the leg.
> 
> e.g.
> ;From   To   Tape   Compass   Clino   L   R   U   D  stn
> 1          2     5.34    234           -6       0.3 0.4 1.4 0.3
> ;The LRUD data is taken to be for stn 1
> 2          3     4.62    246           -2       0.2 0.2 1.3 0.4   3
> ;The LRUD data is taken to be for stn 3 (specified)

I have rather a backlog of Survex work currently, but clean patches to add
useful alternative formats are welcome.

Cheers,
    Olly