[Therion] Placing part of a map below another

[Tarquin Wilton-Jones]

> The "select" statement in the thconfig file turned out to be the answer.  I have never used that before, so I don't understand why my other maps with overlying passage have worked.

Because when you don't select a map, Therion selects *all* scraps that
match the current projection, and draws all of them, using the "average
height" of the scraps to determine stacking order. That often works
well, but there are some cases where it doesn't. See the previous thread
on this mailing list titled "Sorting scraps/maps by height in default mode".

https://www.mail-archive.com/therion@speleo.sk/msg07536.html

> In this case I need to map a map of the lower level because it will contain far more than one scrap.


Yep, there's multiple ways that will work, and you choose what works for
you. You could have a single map, put all the scrap references for the
top layer, then "break" then all the scraps in the next layer, and so
on. Or you can use nested maps to organise it.

Personally, I have at least two maps per survey trip+area (plan, and
elevation), each of which contains multiple scraps. Then for each parent
survey (eg. one region of the cave at a time, or one cave), I have the
same, collecting together the child maps. When doing offsets, I have a
separate map for each "part" (offset or not), and a map to apply the
offsets - again mirrored into the parent surveys. So yeah, maps are used
quite heavily. But they are not essential for layering.

> Break will not work in map definition from maps. Only sequence of particular maps works. 


OK, now how come I didn't know that?!

Whenever I make maps, I have been putting "break" in there, and it has
happened to work because I will always put them in the right order
anyway. It doesn't show any error message, and just silently ignores
them. (It doesn't hurt to have it there, if only just to help mental
understanding of the layers.)

But even the Therion book does it - see the "displaying overlaying maps
in offset" section. When defining "break" it doesn't say that it applies
only to scraps and not maps. And when defining "map" syntax, it actually
shows you putting a map reference, then "break" then another map reference.

This should really be stated very explicitly, since it is not at all
consistent with what the book shows. Are you sure it's not a bug?

I was told previously that maps represent their scraps, so a map that
references two maps could just be thought of as the combined list of
scraps (and breaks) within them. But as you said, it seems to implicitly
add a "break" at the end of each child map.

Could someone authoritatively state the intended behaviour here, because
either a bug needs to be fixed, or the documentation needs to be updated
to match the implementation. I will happily file the required bug report
accordingly.

Cheers :)

Tarquin