LRUD (was Re: Roadmap)

[Olly Betts]

On Fri, Apr 19, 2002 at 02:15:58PM +0100, Wookey wrote:
> On Thu 18 Apr, Olly Betts wrote:
> > 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 [...]

That's why I say "For now".  This simple model cover most cases, and provides a
reasonable simplification for many of the cases it doesn't quite cover.

> I draw L & R arrows on the plan to show the direction of
> measurment in these cases.

And how would you suggest we type in the direction of these arrows?  It's not
impossible, but it's not obvious what the best way to do it is.

> These are common enough that I hesitate to accept
> the 'LRUD is a plane' as a fundamental design principle.

It's not.  It's a simple model (probably the simplest useful one).

> > 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?

Any way people measure the shape of a cave which can be fed into a computer and
turned into a mesh of polygons.

> 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 believe we should be able to cope with all the sane common variants.

On Fri, Apr 19, 2002 at 04:42:04PM +0100, Martin Green wrote:
> Rather than defining planes, an alternative would be to define up and down,
> then a number of horizontal readings.  [...]

Bear in mind that many survey projects has a vast pile of LRUD measurements,
most of which are in a form which the fairly simple scheme I described can make
use of.

There's also the issue that it's best if the data in the .svx file looks very
similar in layout to the data in the survey book.  This makes it a lot easier
to proof-read data entry.

Although we could implement a more elaborate scheme to start with, this would
take longer, and so it won't be ready for people to use as soon.

I've not looked in great detail at how other cave surveying software handles
LRUD, but from what I've seen it mostly seems to be at about the level of the
scheme I outlined.

Cheers,
Olly