[Therion] Colouring an elevation based on surveys that are not being displayed

[Tarquin Wilton-Jones]

> Would the colours for the specific altitudes not be fixed if you used
> lookup?

They would, but the intention was that - rather than having to manually
select all the colours to get the perfect graduation of colours (which
you have to do if you use a lookup table), you could get Therion to
automatically take the height from a map, since it already knows those
heights, and knows exactly how to colour those parts.

I had thought about using lookups, but it feels very clunky as an
approach, since it means manually specifying the altitudes of the
highest and lowest points - manual knowledge of automatically calculated
data.

With a lookup, you need to know exactly the colours it will have
selected for each height that matters. Each time a new piece of passage
gets added to the top or bottom of the cave, which then changes all of
the automatic colouring within the cave, you will have to re-calculate
the lookup colours again for use with your subset maps.

With "altitude-relative caveMP at cave" this would all become automatic.