Interactive Extended Elevations

[Phil Underwood]

On Fri, 23 Jun 2000, Olly Betts <olly@survex.com> wrote:
<SNIP>
>I'm thinking of a fairly small file which says:
>
> * where to start (by default some likely high up and/or fixed point wou=
ld
>   be picked)
>
> * where to force folds (by default heuristics would decide where to fol=
d by
>   looking at the trends in angles between survey legs)

I've tried this using a fairly simple algorithm; comparing the bearing of
the next leg with the previous one. It doesn't work at all well - you ten=
d
to get reversals where you don't expect them, and it doesn't reverse wher=
e
you'd expect it to. I would prefer to have no automatic folding, meaning
that everything has to be done by hand; there are usually only a few fold=
s
required for any particular extension. Also, having automatic folding cou=
ld
result in an extended elevation gaining or losing a fold when (say) anoth=
er
loop is added to the survey, slightly changing the data used, and taking =
a
particular bend over the cut-off for folding. I don't know how often this
would happen, however.=20
>
> * where to break loops (again heuristics can make a default stab)
This is done fairly primitively in my existing extend routine - but it
breaks at junctions, which I agree is poor. Another question (I think thi=
s
was debated before, but I've forgotten if any consensus was agreed) is
whether one specifies a leg or station to break at. Legs are certainly
easier to code for, and what should occur if a 4-node (say) is marked as
breakable?

>
> * where to prune - legs/traverses beyond which whole areas of survey sh=
ould
>   be removed
>
>This is easy to apply to a newer/older version of the same survey.  List=
ing
>individual legs makes this task much harder.
This leads me on to another issue - how do you refer to a leg in such a t=
ext
file? For example,

*begin pedant
1 2  4.51  217 +05
1 2  4.49  216 +04
1 2  4.50  218 +05
*end pedant

How would one refer to the second leg in this file?



>The only slightly tricky case I can see is where a connection is made ba=
ck
>to the EE from excluded survey (e.g. ambidextrous, which connected the r=
ight
>hand route back to the left hand route a couple of hundred metres below
>where they originally split.  But that can be detected automatically (us=
ing
>a node colouring algorithm) and the user prompted about what to do.
Could you send me a brief explanation of what a node colouring algorithm
is? I'm guessing that it probably doesn't actually have much to do with
red,green, blue stuff.

--=20
Phil Underwood <furbrain@furbrain.screaming.net>
Homepage: http://members.xoom.com/bighairyone/
"It's not what you've got, it's how you make it explode."