Colouring by date

[Robert Smallshire]

Hi Olly,

> Erin had a cave which had a vast entrance pitch with a fairly 
> flat cave below, which resulted in all the colours being used 
> up by the entrance pitch, which is similarly annoying.
> 
> We had two ideas to improve that (neither implemented yet).
> 
> One was to make the depth band widths depend on the length of 
> passage at that depth.  More passage gets tighter bands.  But 
> that does mean the colours change as you survey more, even if 
> the cave doesn't get deeper.
> 
> The other was to allow the user to choose the depth band 
> divisions.  But that's kind of fiddly - something automatic 
> is nicer if it works well.

The standard technique for doing this with maps is to compute a cumulative
distribution function of map area by elevation - this gives a so-called
hypsometric curve - which you can use to distribute colors evenly by map
area rather than by elevation. You could do the same with a cave survey -
you just build a cumulative distribution function of passage length w.r.t.
depth and use that to effectively histogram equalize the colour scale so
that you have as much red cave as green cave as blue cave.

Rob Smallshire

Robert Smallshire
robert at smallshire.org.uk
http://smallshire.org.uk/
Currently in Norway (UTC +1 hours)