Spud thoughts

[Wookey]

On Mon 09 Oct, Olly Betts wrote:
> In message <Marcel-1.50-1009144016-bc8h+Ty@chewy.aleph1.co.uk>, Wookey
> writes:


> >Good idea. Any reason why this shouldn't just be another attribute?
> 
> Attributes are meta-data - they don't mean anything to the survey
> processing code, but are just attached and passed along.  This information
> is part of the survey processing (in much the same way that a compass
> reading is).
> 
> I'd expect survey data for legs would be available as attributes, so the
> answer to your question is probably that it is another attribute, but not
> just another attribute.

OK, yes. Lets get the terminology right. I hadn't necessarily been reserving
'attribute' for meta-data.

> >[snip] e.g the
> >Wakulla-II survey device produced a stream of positions. You can draw legs
> >between them (for the route it took) but the stations position the legs
> >rather than the other way round.
> 
> Presumably the stations are located relative to each other using an
> intertial device or similar?  Although you may only get a processed version
> of that data from such an instrument - i.e. displacements from the start to
> each subsequent station, rather than between them.

Exactly. It does indeed measure 'legs' internally, but all you get out of it
is stations. (actually I'm not entirely sure that's true, but it's useful to
consider this case as its a perfectly plausible surveying device).

> The `internal path' may not be internal - for example the survey in Austria
> this year of 1623/188 (a short linear cave with several shaft entrances).
> We surveyed it by plumbing down each entrance from the surface and
> measuring between horizontal distances above ground.

Yes, but those outside legs would be marked 'outside'. Only the plumbs would
be 'inside' (although of course the top of each one is probably a little bit
'outside'. Non-measured 'internal path' legs could be added between the
bottom of the plumbs to give a better idea of the cave shape.

ie I don't think the above counterexample is a convincing argument that
'internal path' is not an edequate generic concept.

> Perhaps `skeleton' is a better term?  You get exo-skeletons after all!
 
yes, it probably is.

> >Deciding what is part of the dataset and what is just an artifect of
> >the representation/display (eg skinned tubes could be either) could be
> >interesting.
> 
> What's a skinned tube?  Are you thinking of tunnel here?

Yes, or the model of a cave in devon produced using rotating ultrasound
scanners. In both cases the dataset only represents cross-sections positioned
on legs (with some other parameters such as direction and tilt) and the
interpolated 'skin' is added as the display/rendering stage. But a more
accurate skin using the cave drawings could be produced in which case the
skin would be data too.

Wookey
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