LRUD (was Re: Roadmap)

[Wookey]

On Thu 18 Apr, Olly Betts wrote:
> On Wed, Apr 03, 2002 at 04:12:07PM +0100, Olly Betts wrote:
> > * Produce a CDROM distribution with all the versions on.

> These are still to do.

I might get inspired and download and blow everything if I get a bit of
spare time (ha!)

> > * Passage dimensions (LRUD), and drawing of "solid" cave models using it.
> >   I'm going to write a separate mail about this.

> For now, the model for a passage cross section is that it's represented by
> 4 perpendicular measurements (e.g. left, right, up, down), all of which lie
> in the same plane.

This is only usually true. I take a lot of L and R readings which don't lie
in the same plane (at odd places where you want to know how far it is to the
nearest wall-corner or the mouth of a passage, not just the obvious
'left/right'). I draw L & R arrows on the plan to show the direction of
measurment in these cases. These are common enough that I hesitate to accept
the 'LRUD is a plane' as a fundamental design principle. Allowing for 2
planes each of which contian some of the readings is one way of dealing with
this. U & D readings alwyas are in the same plane for me (so far!)

Ignoring this would affect only ~5% of readings so it wouldn't be fatal, but
it shouold be considered.


> Other ways of measuring the shape of the cave can be added later too -
> Initially I want to keep it fairly simple, but still useful for the
> majority of surveyors.

Does 'other ways' cover the above or are yoi talking about radically
different other ways?

> Here's roughly what I expect the data would look like in the .svx file:
> The other alternative is:

> *data normal from to tape compass clino
> 1 2  1.23 234 +14
> 2 3 11.46 220 -03

> *data lrud station l r u d
> 1  1.0 0.5 2.0 1.5
> 2  0.0 1.4 1.5 2.0
> 3  0.0 1.2 2.0 2.0

> I'm undecided which is better at present.  Both may be allowed.

This is how I record all my data (and so do a lot of others) and we've
entered an awful lot of data like this so it'd be nice if it was allowed -
the alternative being writing a script to convert it all to some other format
which might well be a similar amount of work to just dealing with it in
survex.

You don't mention the 'which way are we looking' problem. Do you believe this
is now not a problem or something like the 'newl' algorithm will get it
right? I suspect the computer will 'usually' get it right but we may need to
ability to add a 'swap L&R' flag on some stations/readings, for when the
computer doesn't get it right (or the surveyor didn't - although in this casr
you can justify just correcting the data by swapping the readings).

Wookey
-- 
Aleph One Ltd, Bottisham, CAMBRIDGE, CB5 9BA, UK  Tel +44 (0) 1223 811679
work: http://www.aleph1.co.uk/     play: http://www.chaos.org.uk/~wookey/