\section{The parameter \texttt{\Index{visibility}}}

For all projections, the Boolean \Lkeyword{visibility}
(\verb+true+ by default) specifies whether or not to have the
projection made visible.

Set to \verb+false+, the \Index{projection} is always carried out. Set to
\verb+true+, the projection is only carried out when the plane of
projection is visible from the viewpoint of the observer.

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