Cactus Code Thorn SetMask_SphericalSurface
Author(s)    : Frank Löffler
Maintainer(s): Frank Löffler
Licence      : GPLv2+
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1. Purpose

Sets a given mask according to given spherical surfaces and parameters.
One example usage is to set the excision mask based on information from
an apparent horizon finder which is stored as a spherical surface.