[Therion] Hide symbols within certain maps/subsurveys

[Tarquin Wilton-Jones]

Thanks for the suggestions.

> Otherwise perhaps it can be done using custom attributes for the objects?
> It was suggested to me once, but it seemed labour intensive so I never tried
> it.

That sounds like it has promise.

I use a custom slope symbol, which looks different based on whether you
use "-attr type surface" (so on the surface it looks like a pale green
slope, while underground it looks like slope lines). That's one way to
achieve it, but it means that custom metapost would be needed for each
and every symbol that needs to be displayed on the surface, and that
-attr would need to be supplied for every surface symbol so that it
could be detected from metapost as "important to draw this one". Not
terrible, since my surface stuff only uses slopes, pitch, floor step
borders, water flow, sink, rock-border, debris and label. Fairly
minimal. Not pretty, but fairly minimal, and easy enough to maintain. Is
this the general idea you were getting at?

Then there is this other possibility: use "-context line via-ferrata"
(or some other symbol I never use) on every surface symbol. Then in the
layout use symbol-hide for everything unwanted underground, and then
"symbol-show line via-ferrata" to make sure they show up on the surface.
That is ... er ... ugly and not future proof of course, since it could
break if that line ever gets used in a cave (via ferrata won't be used
here).

Likewise, I could potentially use -scale for the surface stuff and then
use min-symbol-scale, but that would be very restrictive about what
could be drawn where in the entire survey.

I had considered Andrew's workaround of embedding a PDF in the right
spot. Figured it was too prone to errors in placement, and would break
whenever new passage was surveyed outside the old area. Not terrible,
just not very easy to maintain.

Grateful for any solutions though. Actually wondering why there is no
dedicated solution of "show this symbol within this map, but hide it
within this other map" though, since it seems like there must be more
use for it...

Cheers,

Tarquin