  We present the Cone of Darkness, an application to automatically configure
blank-sky positions for a series of stacked, wide-field observations, such as
those carried out by the SAMI instrument on the Anglo-Australian Telescope
(AAT). The Sydney-AAO Multi-object Integral field spectrograph (SAMI) uses a
plug-plate to mount its $13 \times 61$ core imaging fibre bundles (hexabundles)
in the optical plane at the telescope's prime focus. To make the most efficient
use of each plug-plate, several observing fields are typically stacked to
produce a single plate. When choosing blank-sky positions for the observations
it is most effective to select these such that one set of 26 holes gives valid
sky positions for all fields on the plate. However, when carried out manually
this selection process is tedious and includes a significant risk of error. The
Cone of Darkness software aims to provide uniform blank-sky position coverage
over the field of observation, within the limits set by the distribution of
target positions and the chosen input catalogues. This will then facilitate the
production of the best representative median sky spectrum for use in sky
subtraction. The application, written in C++, is configurable, making it usable
for a range of instruments. Given the plate characteristics and the positions
of target holes, the software segments the unallocated space on the plate and
determines the position which best fits the uniform distribution requirement.
This position is checked, for each field, against the selected catalogue using
a TAP ADQL search. The process is then repeated until the desired number of sky
positions is attained.
