[Therion] Blended colour by gradient?

[Tarquin Wilton-Jones]

> possible to colour an elevation survey

But then I see that I may have misinterpreted the word "elevation".

You may have meant projected elevation or extended elevation, rather
than plan with elevation colouring. (Ambiguous words!)

My answer still stands about metapost and gradients - it can do them.
You would not need a reference station so much now though, because
simple vertical position on the page would be enough, and it simplifies
things a lot. It would still need to know the relative height of the top
and bottom points of each scrap to know what colours to choose for the
gradient lines (and while I know that can all be done with maths, I am
glad I am not the one doing it, because that doesn't sound fun to me).

But sadly, there are a great many things that would not actually work.
There are a lot of "thclear" (clear this shape) and "thunfill" (un-fill
this shape) commands used in the metapost, which do not just "make this
part transparent". Instead, they re-paint the area with the colour of
the scrap (this is because of how things get layered, and how some
symbols are made from one colour, with what looks like a hole punched
through them by another colour). If you had a gradient fill, those
commands would not be able to choose a colour for that point.

In other words, MetaPost can do gradients, but that is not compatible
with the way that a lot of Therion works.