[NTG-context] Centering a figure vertically on a page

[Marcin Borkowski]

Hello,

the subject line basically covers my problem: I have a large (tikz)
figure, and I want to have it by itself on a page, centered both
horizontally and vertically.  How can I achieve this?  I already know
that \setuppagenumber[state=stop] is a good idea, and \midaligned{...}
gives me horizontal centering; what about vertical?  The problem is
that the figure is larger than the text area (and this doesn't bother
me, it's a game board and it may extend almost to the paper border),
so \vfill doesn't work (and \vss doesn't, either).

TIA

-- 
Marcin Borkowski
http://mbork.pl