LRUD (was Re: Survex digest, Vol 1 #136 - 3 msgs)

[Olly Betts]

On Wed, Aug 01, 2001 at 11:29:58AM -0400, Richard Knapp wrote:
> LRUD are dependant on a shot but there are three ways they can be taken:
> 
> 	- perpendicular to next;
> 	- perpendicular to last;
> 	- average between last and next.

There's more than that - for instance, some people take them "across the
passage".  Roughly speaking this means that the L/R line is perpendicular to
the passage wall where it intersects.  It's actually the obvious distance
for someone to measure when you ask "how far is it to the left wall", and it
can be more useful when drawing the survey by hand.  Harder for the computer
though...

> CRF used to "require" dims at both TO and FROM stations for the yet to be
> developed software for passage modeling (this was back in the 70s and 80s).
> Of course no one recorded the data and if it was, it was never used.

For BCRA grades 5d and 6d you're meant to record the passage detail "at
survey stations and WHENEVER NECESSARY BETWEEN STATIONS to show significant
changes in passage shape, size, direction, etc." (my caps).  So you'll
effectively get LRUD readings part-way along legs...

But in the interests of having something to implement, if you're going to
pick one allowed style then LRUD readings at stations along the leg bisector
is the one to go for.  Others can be added later once the simplest case is
working.

Cheers,
Olly