Spud thoughts

[Olly Betts]

In message <Marcel-1.50-1009144016-bc8h+Ty@chewy.aleph1.co.uk>, Wookey writes:
>On Sat 07 Oct, Olly Betts wrote:
>
>> * Labelled levels of the survey prefix hierarchy - e.g. area, system, cave,
>>   survey book.
>
>Definately a useful concept that will do much to improve useabilty and help
>make graphical project-managemnet tools feasible. However note that 'survey
>book' does not generally correspond to a hierarchical level.

Hmm, true.  Scratch that one.

>It needs to be
>implemneted as an attribute than can be applied to all sorts of bits of data
>potentially widely scattered throughout the dataset.

That's presumably true of many attributes - survey date is an obvious
example.

>An individual surveyor's book can easily have data in it from Wales,
>Yorkshire, Austria and Turkey in it, for example.

Though you are unlikely to want to process those in the same dataset, so
that's not really a good example.

But it makes me think - I didn't include "curvature of the earth" in my
list.  Someone brought that up on the cavers forum a few years back.  I
think the only way in which cave survey software allowed for it was in
translating benchmark positions from UTM.  But if you wanted to view all the
cave passage in a country (or in the world!) it becomes relevant.

Note: I'm not saying this (or anything else on the list) will necessarily go
in, but we should at least think about these things rather than rendering
them impossible arbitrarily.

>> * Concept of relocatable stations - many survey stations are inherently
>>   ephemeral and trying to link another survey to one is clearly a mistake
>>   (or the station wasn't ephemeral in which case its status is wrong).
>
>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.

>> * Polygonal meshes for terrain or scanned chambers.
>> 
>> Any other possibilities? 
>
>[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.

>It also produces a spiral set of wall
>positions. This does not fit too well into the model of 'cross sections
>attached to legs', although it could be made to fit with a bit of effort.

It's somewhere between a series of passage cross-sections and a scanned
mesh.

>For these sorts of novel devices we need concepts a bit like 'internal path'
>which is something that travels through the cave between the walls (and
>current survey centrelines are an example of one) and 'walls' which can be
>represented in all sorts of ways (measurements, X-sects, skinned tubes, dot
>clouds).

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.

Perhaps `skeleton' is a better term?  You get exo-skeletons after all!

>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?

Cheers,
Olly