LRUD (was Re: Roadmap)

[Wookey]

On Fri 19 Apr, Olly Betts wrote:
> 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.

fair enough.

> > 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.

indeed. 

> > 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).

OK. I can go with that.

> > 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.

Good. I just remembered some long emails about how it wasn't possible/very
difficult from a few years back. Lets see how well it works. It'd certainly
be nice to have some LRUD ticks on my plots after all these years, even if a
few of them are in the wrong places.


> 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.

That is true. (or at least that appears to be true - you can't easily tell if
more complex versions are actually possible in most cases) The only one to
have implemented a geuinely versatile LRUD system is Tunnel (I), which
included both tilt angles for each plane, offsets from the station (along a
leg or in an arbitrary direction), a 'swapLR' boolean, an associated pair of
stations and fnally multiple such entities at one station. That covers
evything you can conceive of as well as dealing with the simple case.

Your suggested implementation will have to have an associated pair of tilt
angles and one or two stations (or one leg) - the question is whether/how we
expose them to the data-input system so that the user can specify them (your
suggestion being that we just expose the vertical tilt, allowing it to be set
to 'horizontal'). Adding 'flipLR' and an offset to the data-structure is a
good idea I think, even from the word go. We can worry about how to expose
any or all of these variables to the user later.

Wookey
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